EXHIBIT 4.3

THESE  SECURITIES HAVE NOT BEEN REGISTERED  UNDER THE SECURITIES ACT OF 1933, AS
AMENDED,  OR THE SECURITIES  LAWS OF ANY STATE AND CANNOT BE SOLD OR TRANSFERRED
UNLESS AND UNTIL THEY ARE SO REGISTERED OR UNLESS AN EXEMPTION UNDER SUCH ACT OR
LAWS IS AVAILABLE. THE TRANSFERABILITY OF THESE SECURITIES IS FURTHER SUBJECT TO
THE  PROVISIONS OF A PURCHASE  AGREEMENT  DATED AS OF OCTOBER 21, 1998 AMONG THE
COMPANY AND THE PURCHASERS NAMED THEREIN.


                         CLASS C 13% CONVERTIBLE SENIOR
                         SUBORDINATED DEBENTURE DUE 1999

                                                                October 21, 1998


         LOGIMETRICS,  INC.,  a Delaware  corporation  (the  "Company"),  hereby
promises  to pay to the order of  ____________  (together  with its,  his or her
successors  and assigns,  the  "Holder") the  principal  amount of  ____________
(______________)  in lawful money of the United  States,  together with interest
thereon  calculated  from the date  hereof and  payable in  accordance  with the
provisions of this debenture ("Debenture").

         By accepting this Debenture,  the Holder agrees that the obligations of
the Company to the Holder under this Debenture shall be subordinated only to the
Senior  Debt (as  hereinafter  defined) of the  Company,  all upon the terms set
forth in paragraph 4 hereof.

         This  Debenture  may be  surrendered  for  transfer  or exchange by the
Holder  hereof  upon  surrender  of this  Debenture,  together  with a  properly
completed bond power or other instrument of transfer, and any required signature
guarantees,  at the office of the Company  set forth in Section 11 hereof.  Upon
proper surrender,  the Company shall issue one or more replacement Debentures of
like tenor  registered  in the names and in the  denominations  requested by the
surrendering Holder and dated the date of issuance thereof;  provided,  however,
that (i) appropriate  adjustments shall be made to reflect the date of issue and
principal  amount  of  each  such  replacement  Debenture,  (ii)  the  aggregate
principal amount of all Debentures shall be limited to $2,666,667,  and (iii) no
Debenture  shall be issued in a principal  amount of less than $5,000  unless in
connection  with a  transfer  resulting  from the  complete  liquidation  of the
original Holder of this Debenture. All Debentures shall rank pari passu.

          1. Payment of Interest.  Interest  will accrue from the date hereof at
the rate of thirteen  percent (13%) per annum on the unpaid  principal amount of
this Debenture  outstanding from time to time on the basis of a 360-day year for
the actual  number of days elapsed.  Subject to paragraph 4 hereof,  the Company
will pay to the Holder all accrued  and unpaid  interest  on this  Debenture  on
January  15,  1999 and  quarterly  thereafter,  in  arrears,  on the 15th day of
January, the 15th day of April, the 15th day of July and the 15th day of October
(each, an "Interest  Payment Date") to and including the earlier to occur of the
Conversion Date  (hereinafter  defined) or the Due Date  (hereinafter  defined).

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Interest  will accrue at the greater of the Default Rate  (hereinafter  defined)
and the rate of fifteen  percent (15%) per annum on any  principal  payment past
due under this Debenture and, unless  prohibited under applicable law (and if so
prohibited then only to the extent not so prohibited), on any interest which has
not been paid on the date on which it is due and payable  (without giving effect
to any  applicable  grace  periods  or  paragraph  4 hereof)  until such time as
payment therefor is actually delivered to the Holder.

          2. Payment of Principal on Debenture.

               (a)  Scheduled  Payments.  The Company  will repay the  principal
amount of this Debenture on September 30, 1999 ("Due Date").

               (b) Optional  Prepayment.  The Company may at any time  hereafter
prepay,  without  premium  or  penalty,  all  (but  not  less  than  all) of the
outstanding  principal amount of the Debentures,  together with interest accrued
on such prepaid amount to the date of payment.

               (c)  Mandatory  Prepayment.  The Company  shall  prepay,  without
premium or  penalty,  all (but not less than all) of the  outstanding  principal
amount of the Debentures,  together with interest accrued on such prepaid amount
to the date of  prepayment  within forty (40) days after the  consummation  of a
Qualifying Offering.  As used herein,  "Qualifying Offering" means the public or
private  sale by the  Company  of debt or  equity  securities  resulting  in net
proceeds to the Company  (after the  deduction  for all  necessary and customary
expenses  payable  by the  Company  in  connection  therewith)  of at least  $15
million.

               (d) Notice of Prepayment. The Company will give written notice of
its election to prepay this  Debenture to the Holder in person or by  registered
or certified mail, return receipt  requested,  at least thirty (30) and not more
than  forty-five  (45)  days  prior  to the date of  prepayment.  On the date of
prepayment  specified in the Company's  notice,  the Company will deliver to the
Holder of this  Debenture in person or by registered or certified  mail,  return
receipt  requested,  a cashier's or certified  check for the entire  outstanding
principal  amount being  prepaid,  together  with all accrued  interest  thereon
through the date of prepayment.

          3. Intentionally Omitted.

          4.  Subordination.   The  Company's  payment,   whether  voluntary  or
involuntary,  whether in cash, property,  securities or otherwise and whether by
application  of  offset  or  otherwise  (hereinafter  "Payment")  of  any of its
obligations under this Debenture shall be subject to the following restrictions:

               (a)  Subordination to Senior Debt.  Anything in this Debenture to
the contrary  notwithstanding,  the obligations of the Company in respect of the
principal of and interest  (including  any premium or penalty) on this Debenture
and any other amounts due under this Debenture (the  "Subordinated  Debt") shall
be subordinate  and junior in right of payment,  to the extent and in the manner
hereinafter set forth, to the Senior Debt. "Senior Debt", when used with respect

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to the Company,  means only the following (and no other indebtedness of any kind
or  nature  whatsoever):  (i) the  Company's  indebtedness  to North  Fork  Bank
("Bank") under (A) that certain $640,000.04 Restated and Amended Term Loan Note,
dated April 25, 1997, and (B) that certain $2,200,000  Modified Revolving Credit
Note,  dated April 30, 1998, in each case,  together  with interest  thereon and
(ii) renewals, extensions, refinancings, deferrals, restructurings,  amendments,
modifications  and waivers of the  indebtedness  described  in clause (i) above;
provided, however, that the principal amount of the Senior Debt shall not exceed
$2.8 million.

               (b)  Default on Senior  Debt.  So long as the Senior Debt has not
been paid in full, if there shall occur a default in the payment when due of any
amount  due and owing on account of Senior  Debt (any of the  foregoing  being a
"Senior  Debt  Default")  then,  from and after the  receipt of  written  notice
thereof from the holder of Senior Debt unless and until such Senior Debt Default
shall have been  remedied or waived the Company will not make any Payment on any
Subordinated  Debt,  and the  Holders of  Subordinated  Debt will not receive or
accept any direct or indirect  Payment in respect  thereof,  and the Company may
not redeem or otherwise acquire any Subordinated Debt.

               (c) Changes in Senior Debt. Any holder of Senior Debt may, at any
time and from time to time, without the consent of, or notice to, the Holder and
without  incurring  responsibility  to the  Holder,  and  without  impairing  or
releasing the obligations of the Holder hereunder:

                    (i) Change the  manner,  place or terms of payment or change
          or extend the time of payment of or renew or alter the Senior  Debt or
          any  portion  thereof;  provided,  however,  that  without the written
          consent of the Majority  Holders  (hereinafter  defined) the principal
          amount of and  interest  rate  applicable  from time to time to Senior
          Debt may not be  increased  (other  than  pursuant to the terms of the
          Senior Debt as such terms existed on the date of issuance hereof);

                    (ii)  Sell,  exchange,  release or  otherwise  deal with any
          collateral   securing  the  Senior  Debt  or  any  other  property  by
          whomsoever  at any time  pledged or  mortgaged  to secure,  or however
          securing, the Senior Debt or any portion thereof; and

                    (iii) Apply any sums by whomsoever paid or however  released
          to the Senior Debt or any portion thereof.

               (d) Consent to Senior Debt. By acceptance of this Debenture,  the
Holder hereby consents to the making of Senior Debt and hereby acknowledges that
each current and future holder of Senior Debt has relied, and in the future will
rely, upon the terms of this Debenture. The holders of Senior Debt shall have no
liability to the Holder and the Holder hereby waives any claim which it may have
now or  hereafter  against  any holder of Senior Debt  arising  from any and all
actions  which any holder of Senior  Debt may take or omit to take in good faith
with regard to the Senior Debt or its rights or obligations hereunder.

<PAGE>

               (e)  Payments in Trust.  Until the Senior Debt has been repaid in
full, in the event the Holder shall receive any Payment in  contravention of the
provisions  of  this   paragraph  4  including,   Payments   arising  under  the
subordination  provisions of any other  indebtedness of the Company,  the Holder
shall hold all such Payments so received in trust for the holders of Senior Debt
and shall forthwith turn over all such Payments to the holders of Senior Debt in
the form  received  (except for the  endorsement  or assignment of the Holder as
necessary,  without recourse or warranty) to be applied to payment of the Senior
Debt whether or not then due and  payable.  Any Payment so received in trust and
turned  over to the  holders  of Senior  Debt  shall not be deemed a Payment  in
satisfaction of the Subordinated Debt by the Company.

               (f) Payment in full of Senior Debt;  Subrogation.  If any Payment
to which a Holder of  Subordinated  Debt would  otherwise have been entitled but
for the provisions of this paragraph 4 shall have been applied,  pursuant to the
provisions of this paragraph 4, to the payment of Senior Debt,  then and in such
case, the Holder of the Subordinated  Debt (i) shall be entitled to receive from
the holders of Senior Debt at the time outstanding any payments or distributions
received by such  holders of Senior Debt in excess of the amount  sufficient  to
pay all  Senior  Debt  in cash in full  (whether  or not  then  due),  and  (ii)
following  payment of the Senior Debt in full,  shall be subrogated to any right
of the  holders  of Senior  Debt to  receive  any and all  further  payments  or
distributions  applicable to Senior Debt, until all the Subordinated  Debt shall
have been paid in full. If the Holder of the  Subordinated  Debt shall have been
subrogated  to the rights of the holders of Senior Debt due to the  operation of
this paragraph 4(f), the Company agrees to take all such  reasonable  actions as
are  requested by such Holders of the  Subordinated  Debt in order to cause such
Holders to be able to obtain  payments  from the  Company  with  respect to such
subrogation rights as soon as possible.

               (g) No Impairment of the Company's Obligations. Nothing contained
in this  paragraph  4, as between the Company and the Holder of this  Debenture,
shall impair the obligation of the Company, which is absolute and unconditional,
to pay to the Holder the principal of and interest on this Debenture as and when
the same shall become due and payable in accordance with the terms hereof.

               (h) Advances in Reliance.  The Holder of this  Debenture,  by its
acceptance hereof,  agrees that each holder of Senior Debt has advanced funds or
may in the  future  advance  funds in  reliance  upon the terms  and  conditions
hereof.

               (i)  Non-Waiver of Rights.  No right of any holder of Senior Debt
to enforce its right of  subordination  as herein  provided shall at any time in
any way be  prejudiced  or  impaired by any act or failure to act on the part of
the  Company,  or by any act or  failure  to act by any such  holder,  or by any
non-compliance  by the Company with the terms,  provisions and covenants of this
Debenture,  regardless of any  knowledge  thereof any such holder may have or be
otherwise charged with.

               (j)  Recaptured  Payments.  Any Payments  received by a holder of
Senior  Debt  from the  Company  or the  Holder  which,  in  connection  with an
Insolvency Event or Proceeding (hereinafter defined), is required to be remitted

<PAGE>

to the payor or the bankrupt estate shall not be deemed a Payment to such holder
of Senior Debt for all purposes hereunder.

               (k)  Right  to  Convert  Unaffected.  Nothing  contained  in this
Section 4 shall be  construed  so as to limit or  restrict  the  ability  of the
Holder to convert this Debenture in accordance with the terms hereof.

          5. Intentionally Omitted.

          6. Conversion Rights.

               (a) From and after the earliest of (i) January 31, 1999, (ii) the
consummation of a Qualifying Offering, or (iii) the date of any repayment notice
given by the  Company  pursuant  to  Section  2(d)  hereof,  the  Holder of this
Debenture shall have the right (the "Conversion Right"), exercisable at his, her
or its option at any time during which the principal amount of this Debenture is
outstanding,  to convert  this  Debenture,  but only in whole,  into a number of
fully  paid and  non-assessable  shares  equal  to (i) the  result  obtained  by
dividing the stated  principal  amount of this Debenture by the conversion  rate
established  for any equity security  issued in a Qualifying  Offering,  if this
Debenture is converted on or after the consummation of a Qualifying Offering, or
(ii) if no Qualifying Offering has occurred on or prior to such conversion,  the
result obtained by dividing the stated principal amount of this Debenture by (X)
$0.52 per share if this  Debenture is converted on or prior to January 31, 1999,
(Y) $0.45 per share if this  Debenture is converted on or after February 1, 1999
and on or prior to April 30, 1999,  or (Z) $0.31 per share if this  Debenture is
converted on or after May 1, 1999.  The respective  conversion  prices set forth
above  shall be  subject to  adjustment  in certain  circumstances  as  provided
herein.  The  conversion  price in effect at the time of the  conversion of this
Debenture is hereinafter  referred to as the  "Conversion  Price." No fractional
shares shall be issuable upon the conversion of this  Debenture.  In lieu of any
such fractional share interest,  upon conversion the Holder shall be entitled to
a cash payment equal to such  fractional  interest  multiplied by the Conversion
Price in effect at the time of such conversion.

               (b) The Conversion  Right is  exercisable  upon surrender of this
Debenture,  together with a conversion  notice,  in the form attached  hereto as
Exhibit A, duly executed and completed, evidencing the election of the Holder to
exercise the Conversion  Right, at the Company's  principal office at 50 Orville
Drive,  Bohemia,  New York 11716.  The registered  owner of this Debenture shall
become the record holder of the shares of Common Stock issuable upon  conversion
as of the date of exercise of the Conversion Right (the "Conversion  Date"). The
shares  issued in  connection  with the  Conversion  Right  shall be  registered
initially in the name of the Holder,  and  delivered to the Holder no later than
two (2) business days after receipt of a properly  completed  conversion notice.
Upon conversion, the Company shall pay to the Holder accrued but unpaid interest
on this Debenture up to, but excluding, the Conversion Date.

               (c) In case,  at any time or from time to time  after the date of
issuance of this Debenture  ("Issuance  Date"),  the Company shall issue or sell
shares of its Common  Stock  (other  than any  Common  Stock  issuable  upon the
exercise or conversion of (i) the Debentures (and any  replacement  Debenture or
Debentures  issued  upon  transfer  or  exchange  of this  Debenture),  (ii) the

<PAGE>

Company's Class A 13% Convertible Senior Subordinated Pay-in-Kind Debentures due
1999 (the "Class A Debentures")  (and any replacement Class A Debenture or Class
A Debentures issued upon transfer or exchange of the Class A Debentures),  (iii)
any additional  securities issued in lieu of cash interest  otherwise payable on
the Class A  Debentures  (the "Class A Accrued  Interest  Debentures")  (and any
replacement  Class A Accrued  Interest  Debenture  or Class A  Accrued  Interest
Debentures  issued upon  transfer  or  exchange of the Class A Accrued  Interest
Debentures),  (iv) the Company's  Amended and Restated  Class B 13%  Convertible
Senior Subordinated  Pay-in-Kind  Debentures due 1999 (the "Class B Debentures")
(and any  replacement  Class B  Debenture  or  Class B  Debentures  issued  upon
transfer or exchange of the Class B Debentures),  (v) any additional  securities
issued in lieu of cash interest otherwise payable on the Class B Debentures (the
"Class B Accrued  Interest  Debentures")  (and any  replacement  Class B Accrued
Interest  Debenture or Class B Accrued Interest  Debentures issued upon transfer
or  exchange  of the  Class B  Accrued  Interest  Debentures),  (vi)  securities
outstanding  on the date  hereof,  (vii) awards made from and after the Issuance
Date  pursuant to the Company's  Stock  Compensation  Program (the  "Plan"),  or
(viii)  awards made from and after the Issuance  Date  pursuant to any incentive
compensation plan or arrangement approved by the Company's Board of Directors or
by the Compensation  Committee of the Company's Board of Directors subject to an
aggregate  limit of 2,000,000  shares of Common Stock for issuances  pursuant to
clauses (vii) and (viii) (subject to adjustment in the  circumstances  set forth
in the Plan or such arrangements) (such securities,  collectively,  the "Subject
Securities")  for a consideration  per share less than the Conversion Price (the
"Trigger  Price"),  or,  if a Pro  Forma  Adjusted  Trigger  Price  (hereinafter
defined)  shall be in effect as provided  below in this paragraph (c), then less
than such Pro Forma Adjusted Trigger Price per share, then and in each such case
the  Holder  of this  Debenture,  upon the  conversion  hereof  as  provided  in
paragraph  (a) hereof,  shall be  entitled to receive,  in lieu of the shares of
Common Stock  theretofore  receivable upon the conversion of this  Debenture,  a
number of shares of Common Stock determined by (a) dividing the Trigger Price by
a Pro Forma Adjusted Trigger Price per share to be computed as provided below in
this paragraph (c), and (b) multiplying the resulting  quotient by the number of
shares of Common  Stock into which this  Debenture  is then  convertible.  A Pro
Forma  Adjusted  Trigger  Price per share  shall be the price  computed  (to the
nearest cent, a fraction of half cent or more being considered a full cent):

                  by  dividing  (i)  the  sum  of (x)  the  result  obtained  by
                  multiplying  the  number  of  shares  of  Common  Stock of the
                  Company outstanding immediately prior to such issue or sale by
                  the Trigger Price (or, if a Pro Forma  Adjusted  Trigger Price
                  shall be in effect, by such Price), and (y) the consideration,
                  if any,  received by the Company  upon such issue or sale,  by
                  (ii) the  number  of shares  of  Common  Stock of the  Company
                  outstanding immediately after such issue or sale.

For the purpose of this paragraph (c):

                    (i) In case the  Company  splits its  Common  Stock or shall
          declare any dividend,  or make any other distribution,  upon any stock
          of the Company of any class payable in Common  Stock,  or in any stock
          or  other  securities  directly  or  indirectly  convertible  into  or
          exchangeable  for Common  Stock  (any such  stock or other  securities

<PAGE>

          being  hereinafter  called  "Convertible  Securities"),   such  split,
          declaration or distribution shall be deemed to be an issue or sale (as
          of the record  date for such split,  dividend or other  distribution),
          without  consideration,  of such  Common  Stock  or  such  Convertible
          Securities, as the case may be.

                    (ii) In case the Company shall issue or sell any Convertible
          Securities  other  than  the  Subject   Securities,   there  shall  be
          determined the price per share for which Common Stock is issuable upon
          the conversion or exchange thereof,  such  determination to be made by
          dividing (a) the total amount received or receivable by the Company as
          consideration  for the issue or sale of such  Convertible  Securities,
          plus the minimum aggregate amount of additional consideration, if any,
          payable to the Company upon the conversion or exchange thereof, by (b)
          the maximum  number of shares of Common Stock of the Company  issuable
          upon the conversion or exchange of all such Convertible Securities.

                    If the price per share so determined  shall be less than the
          Trigger Price (or, if a Pro Forma  Adjusted  Trigger Price shall be in
          effect,  less than such  Price) as of the date of such  issue or sale,
          then  such  issue or sale  shall be  deemed to be an issue or sale for
          cash (as of the date of issue or sale of such Convertible  Securities)
          of such  maximum  number of  shares  of Common  Stock at the price per
          share so  determined,  provided that, if such  Convertible  Securities
          shall by their terms  provide for an increase or  increases,  with the
          passage of time,  in the amount of additional  consideration,  if any,
          payable  to  the  Company,  or in  the  rate  of  exchange,  upon  the
          conversion or exchange  thereof,  the Pro Forma Adjusted Trigger Price
          per share shall,  forthwith upon any such increase becoming effective,
          be readjusted to reflect the same,  and provided,  further,  that upon
          the  expiration  of such  rights of  conversion  or  exchange  of such
          Convertible Securities,  if any thereof shall not have been exercised,
          the Pro Forma  Adjusted  Trigger  Price per share shall  forthwith  be
          readjusted and thereafter be the price which it would have been had an
          adjustment been made on the basis that the only shares of Common Stock
          so issued or sold were  those  issued or sold upon the  conversion  or
          exchange of such Convertible Securities,  and that they were issued or
          sold for the consideration  actually received by the Company upon such
          conversion  or  exchange,  plus the  consideration,  if any,  actually
          received by the Company for the issue or sale of all such  Convertible
          Securities which shall have been converted or exchanged.

                    (iii) In case the Company  shall grant any rights or options
          to subscribe  for,  purchase or otherwise  acquire Common Stock of any
          class other than the Subject Securities, there shall be determined the
          price per share for which Common  Stock is issuable  upon the exercise
          of such rights or options,  such  determination to be made by dividing
          (a) the total amount, if any, received or receivable by the Company as
          consideration  for the  granting of such  rights or options,  plus the
          minimum aggregate amount of additional consideration,  if any, payable
          to the Company upon the exercise of such rights or options, by (b) the
          maximum number of shares of Common Stock issuable upon the exercise of
          such rights or options.

<PAGE>

                    If the price per share so determined  shall be less than the
          Trigger Price (or, if a Pro Forma  Adjusted  Trigger Price shall be in
          effect,  less than such  Price) as of the date of such  issue or sale,
          then the  granting of such rights or options  shall be deemed to be an
          issue or sale for cash (as of the date of the  granting of such rights
          or options) of such  maximum  number of shares of Common  Stock at the
          price  per  share so  determined,  provided  that,  if such  rights or
          options  shall by their terms  provide  for an increase or  increases,
          with the passage of time, in the amount of  additional  consideration,
          if any,  payable to the Company  upon the  exercise  thereof,  the Pro
          Forma Adjusted Trigger Price per share shall,  forthwith upon any such
          increase  becoming  effective,  be readjusted to reflect the same, and
          provided, further, that upon the expiration of such rights or options,
          if any thereof shall not have been  exercised,  the Pro Forma Adjusted
          Trigger Price per share shall  forthwith be readjusted  and thereafter
          be the price which it would have been had an  adjustment  been made on
          the basis that the only shares of Common  Stock so issued or sold were
          those  issued or sold upon the  exercise of such rights or options and
          that they were issued or sold for the consideration  actually received
          by the Company upon such  exercise,  plus the  consideration,  if any,
          actually  received by the Company for the  granting of all such rights
          or options, whether or not exercised.

                    (iv) In case the  Company  shall grant any rights or options
          to subscribe for, purchase or otherwise acquire Convertible Securities
          other than the Subject Securities,  such Convertible  Securities shall
          be deemed,  for the purposes of subparagraph (iii) above, to have been
          issued or sold for the total  amount  received  or  receivable  by the
          Company as  consideration  for the  granting of such rights or options
          plus the minimum aggregate amount of additional consideration, if any,
          payable to the  Company  upon the  exercise of such rights or options,
          provided that,  upon the expiration of such rights or options,  if any
          thereof shall not have been exercised,  the Pro Forma Adjusted Trigger
          Price per share shall  forthwith be readjusted  and  thereafter be the
          price  which it would have been had an  adjustment  been made upon the
          basis  that the only  Convertible  Securities  so  issued or sold were
          those  issued or sold upon the  exercise of such rights or options and
          that they were issued or sold for the consideration  actually received
          by the Company upon such  exercise,  plus the  consideration,  if any,
          actually  received by the Company for the  granting of all such rights
          or options, whether or not exercised.

                    (v) In case any shares of stock or other  securities,  other
          than Common Stock of the Company, shall at any time be receivable upon
          the conversion of this Debenture, and in case any additional shares of
          such stock or any  additional  such  securities (or any stock or other
          securities  convertible  into or  exchangeable  for any such  stock or
          securities) shall be issued or sold for a consideration per share such
          as to dilute the purchase rights evidenced by this Debenture, then and
          in each such case the Pro Forma Adjusted Trigger Price per share shall
          forthwith be adjusted,  substantially in the manner provided for above
          in this  paragraph  (c), so as to protect the Holder of this Debenture
          against the effect of such dilution.

<PAGE>

                    (vi) In case any  shares  of  Common  Stock  or  Convertible
          Securities  or any rights or options to  subscribe  for,  purchase  or
          otherwise acquire any Common Stock or Convertible  Securities shall be
          issued or sold for cash, the consideration  received therefor shall be
          deemed  to be the  amount  received  by the  Company  therefor,  after
          deducting  any  expenses  incurred  and any  underwriting  or  similar
          commissions,  compensation  or  concessions  paid  or  allowed  by the
          Company in connection with such issue or sale.

                    (vii) In case any  shares  of  Common  Stock or  Convertible
          Securities  or any rights or options to  subscribe  for,  purchase  or
          otherwise acquire any Common Stock or Convertible  Securities shall be
          issued or sold for a consideration other than cash (or a consideration
          which  includes cash and other  assets) then,  for the purpose of this
          paragraph  (c), the Board of Directors of the Company  shall  promptly
          determine the fair value of such consideration, and such Common Stock,
          Convertible Securities, rights or options shall be deemed to have been
          issued or sold on the date of such  determination in good faith.  Such
          value shall not be more than the amount at which such consideration is
          recorded in the books of the Company for accounting purposes except in
          the case of an  acquisition  accounted  for on a pooling  of  interest
          basis.  In case any  Common  Stock or  Convertible  Securities  or any
          rights or options to subscribe for,  purchase or otherwise acquire any
          Common  Stock  or  Convertible  Securities  shall  be  issued  or sold
          together with other stock or securities or other assets of the Company
          for a  consideration  which covers both, the Board of Directors of the
          Company  shall  promptly  determine  in good  faith  what  part of the
          consideration so received is to be deemed to be the  consideration for
          the issue or sale of such Common Stock or  Convertible  Securities  or
          such rights or options.

                    The  Company   covenants   and  agrees   that,   should  any
          determination  of fair  value of  consideration  or of  allocation  of
          consideration  be made  by the  Board  of  Directors  of the  Company,
          pursuant to this subparagraph  (vii), it will, not less than seven (7)
          days after any and each such  determination,  deliver to the Holder of
          this  Debenture  a  certificate  signed  by  the  President  or a Vice
          President and the  Treasurer or an Assistant  Treasurer of the Company
          reciting such value as thus determined and setting forth the nature of
          the transaction for which such  determination was required to be made,
          the nature of any  consideration,  other than cash,  for which  Common
          Stock,  Convertible Securities,  rights or options have been or are to
          be issued, the basis for its valuation, the number of shares of Common
          Stock which have been or are to be issued,  and a  description  of any
          Convertible Securities, rights or options which have been or are to be
          issued, including their number, amount and terms.

                    (viii)  In case  the  Company  shall  take a  record  of the
          holders  of  shares  of its  stock of any  class  for the  purpose  of
          entitling them (a) to receive a dividend or a distribution  payable in
          Common Stock or in  Convertible  Securities,  or (b) to subscribe for,
          purchase or otherwise acquire Common Stock or Convertible  Securities,
          then such  record  date shall be deemed to be the date of the issue or

<PAGE>

          sale of the Common  Stock issued or sold or deemed to have been issued
          or sold upon the  declaration  of such  dividend or the making of such
          other  distribution,  or the date of the  granting  of such  rights of
          subscription, purchase or other acquisition, as the case may be.

                    (ix) The number of shares of Common Stock outstanding at any
          given  time  shall  include  shares   issuable  in  respect  of  scrip
          certificates  issued in lieu of fractions  of shares of Common  Stock,
          but shall exclude shares in the treasury of the Company.

                    (x) Following  each  computation  or  readjustment  of a Pro
          Forma  Adjusted  Trigger Price as provided in this  paragraph (c), the
          newly  computed or adjusted  Pro Forma  Adjusted  Trigger  Price shall
          remain in effect until a further  computation or readjustment  thereof
          is required by this paragraph (c).

                    (xi) In case at any  time  or from  time to time  after  the
          Issuance  Date the  holders of the Common  Stock of the Company of any
          class (or any other  shares of stock or other  securities  at the time
          receivable upon the exercise of this  Debenture)  shall have received,
          or,  on or after  the  record  date  fixed  for the  determination  of
          eligible stockholders, shall have become entitled to receive:

                                    (A)  other  or  additional  stock  or  other
                  securities or property (other than cash) by way of dividend;

                                    (B) any cash paid or payable  out of capital
                  or  paid-in  surplus  or  surplus  created  as a  result  of a
                  revaluation of property by way of dividend; or

                                    (C) other or  additional  (or less) stock or
                  other  securities  or  property  (including  cash)  by  way of
                  stock-split, spin-off, split-off, split-up,  reclassification,
                  combination of shares or similar corporate rearrangement;

(other than additional  shares of Common Stock issued to holders of Common Stock
as a stock  dividend or  stock-split,  adjustments  in respect of which shall be
covered by the provisions of this paragraph  (c)),  then in each case the Holder
of this  Debenture,  upon the  conversion  hereof as provided in  paragraph  (a)
hereof, shall be entitled to receive, in lieu of, or in addition to, as the case
may be, the shares theretofore receivable upon the conversion of this Debenture,
the amount of stock or other securities or property (including cash in the cases
referred  to in clauses (B) and (C) above)  which such Holder  would hold on the
date of such  exercise  if, on the  Issuance  Date,  he,  she or it had been the
holder of record of the  number of shares of Common  Stock of the  Company  into
which this Debenture is convertible and had  thereafter,  during the period from
the Issuance Date to and including  the date of such  conversion,  retained such
shares  and/or all other or  additional  (or less) stock or other  securities or
property  (including cash in the cases referred to in clauses (B) and (C) above)
receivable by him, her or it as aforesaid  during such period,  giving effect to
all adjustments  called for during such period by paragraph (c) and subparagraph
(xii) hereof.

<PAGE>

                    (xii) In case of any  reorganization  of the Company (or any
          other  corporation  the stock or other  securities of which are at the
          time  deliverable on the conversion of this Debenture)  after the date
          hereof,  or in case,  after such date,  the Company (or any such other
          corporation) shall consolidate with or merge into another  corporation
          or convey all or substantially all its assets to another  corporation,
          then and in each such  case the  Holder  of this  Debenture,  upon the
          conversion  hereof as provided in  paragraph  (a) hereof,  at any time
          after the consummation of such reorganization,  consolidation,  merger
          or  conveyance,  shall  be  entitled  to  receive  the  stock or other
          securities  or property to which such Holder would have been  entitled
          upon such  consummation  if such Holder had converted  this  Debenture
          immediately  prior  thereto,  all  subject to further  adjustments  as
          provided for herein;  in each such case,  the terms of this  Debenture
          shall be  applicable  to the  shares of stock or other  securities  or
          property  receivable  upon the conversion of this Debenture after such
          consummation.

                    (xiii) The Company  will not, by amendment of its charter or
          through reorganization,  consolidation,  merger, dissolution,  sale of
          assets  or any  other  voluntary  action,  avoid or seek to avoid  the
          observance or performance of any of the terms of this  Debenture,  but
          will at all times in good faith assist in the carrying out of all such
          terms and in the  taking of all such  action  as may be  necessary  or
          appropriate  in order to  protect  the  rights  of the  Holder  hereof
          against dilution or other impairment.  Without limiting the generality
          of the  foregoing,  the Company will not increase the par value of any
          shares of stock receivable upon the conversion of this Debenture above
          the amount payable therefor upon such exercise,  and at all times will
          take all such action as may be necessary or  appropriate in order that
          the  Company   may   validly   and   legally   issue  fully  paid  and
          non-assessable stock upon the conversion of this Debenture.

                    (xiv) In each case of an  adjustment in the number of shares
          of Common Stock or other stock,  securities or property  receivable on
          the conversion of this Debenture, at the request of the Holder of this
          Debenture the Company at its expense shall promptly cause  independent
          public accountants of recognized standing, selected by the Company, to
          compute such adjustment in accordance with the terms of this Debenture
          and prepare a certificate setting forth such adjustment and showing in
          detail  the facts upon which such  adjustment  is based,  including  a
          statement of (A) the  consideration  received or to be received by the
          Company  for any  additional  shares  issued or sold or deemed to have
          been  issued  or sold,  (B) the  number  of  shares  of  Common  Stock
          outstanding or deemed to be outstanding and (C) the Pro Forma Adjusted
          Trigger  Price.  The Company will  forthwith  mail a copy of each such
          certificate to the Holder of this Debenture.

                    (xv) In case:

                                    (A) the  Company  shall take a record of the
                  holders of its Common Stock (or other stock or  securities  at
                  the time  deliverable  upon the conversion of this  Debenture)
                  for the purpose of entitling  or enabling  them to receive any
                  dividend (other than a cash or stock dividend at the same rate

<PAGE>

                  as the rate of the last  cash or  stock  dividend  theretofore
                  paid) or other  distribution,  or to exercise  any  preemptive
                  right  pursuant to the  Company's  charter,  or to receive any
                  right to subscribe  for or purchase any shares of stock of any
                  class or any other securities,  or to receive any other right;
                  or

                                    (B) of  any  capital  reorganization  of the
                  Company,  any  reclassification  of the  capital  stock of the
                  Company,  any  consolidation  or merger of the Company with or
                  into  another  corporation,   or  any  conveyance  of  all  or
                  substantially  all of the  assets of the  Company  to  another
                  corporation; or

                                    (C)  of   the   voluntary   or   involuntary
                  dissolution, liquidation or winding up of the Company;

then,  and in each such case, the Company will mail or cause to be mailed to the
Holder of this Debenture a notice  specifying,  as the case may be, (i) the date
on which a record is to be taken for the purpose of such dividend,  distribution
or right, and stating the amount and character of such dividend, distribution or
right,  or  (ii)  the  date  on  which  such  reorganization,  reclassification,
consolidation,  merger, conveyance, dissolution, liquidation or winding up is to
take  place,  and the times,  if any is to be fixed,  as of which the holders of
record  of  Common  Stock  (or  such  other  stock  or  securities  at the  time
deliverable  upon the exercise of this Debenture)  shall be entitled to exchange
their  shares of Common  Stock of any class (or such other stock or  securities)
for   reclassification,    consolidation,   merger,   conveyance,   dissolution,
liquidation  or winding up or (iii) the  amount  and  character  of the stock or
other  securities  proposed to be issued or granted,  the date of such  proposed
issuance  or grant and the  persons  or class of  persons  to whom such stock or
other  securities  are to be offered,  issued or granted.  Such notice  shall be
mailed at least thirty (30) days prior to the date therein specified.

                    (xvi)  The  Company  will  at all  times  reserve  and  keep
          available,  solely for issuance and delivery  upon the  conversion  of
          this  Debenture  and other similar  Debentures,  such shares of Common
          Stock and other  stock,  securities  and property as from time to time
          shall be issuable  upon the exercise of this  Debenture  and all other
          similar Debentures at the time outstanding.

                    (xvii) Upon receipt of evidence  reasonably  satisfactory to
          the Company of the loss,  theft,  destruction  or  mutilation  of this
          Debenture  and (in the  case  of  loss,  theft  or  destruction)  upon
          delivery  of  an   indemnity   agreement   in  an  amount   reasonably
          satisfactory to it, or (in the case of mutilation)  upon surrender and
          cancellation  thereof,  the Company will issue, in lieu thereof, a new
          Debenture of like tenor.

      7.  Covenants.

          (a) Affirmative  Covenants:  The Company will, and with respect to the
agreements set forth in subsections  (i) through (viii) hereof,  will cause each
subsidiary to:

<PAGE>

               (i) with respect to its properties, assets and business, maintain
     insurance against loss or damage,  to the extent that property,  assets and
     businesses  of similar  character  are  usually  so  insured  by  companies
     similarly situated and operating like properties, assets or businesses with
     responsible insurance companies satisfactory to the Majority Holders;

               (ii) duly pay and discharge all taxes or other claims which might
     become a lien upon any of its  properties  except to the  extent  that such
     items are being in good faith appropriately contested;

               (iii) maintain,  preserve and keep its properties in good repair,
     working order and condition, and make all reasonable repairs, replacements,
     additions, betterments and improvements thereto;

               (iv) conduct its business in substantially the same manner and in
     substantially  the same  fields  as such  business  is now  carried  on and
     conducted;

               (v) comply with all statutes,  rules and regulations and maintain
     its corporate existence;

               (vi) provide the Holder with the following financial information:

                    (A) annually, as soon as available,  but in any event within
          one hundred  twenty (120) days after the last day of each fiscal year,
          audited financial statements,  including balance sheets as of the last
          day of the fiscal year and statements of income and retained  earnings
          and changes in financial  condition for such fiscal year each prepared
          in  accordance   with  generally   accepted   accounting   principles,
          consistently  applied  ("GAAP")  for the period  and prior  periods by
          independent Certified Public Accountants  satisfactory to the Majority
          Holders; provided,  however, that the Company shall have until January
          31, 1999 to deliver the financial statements for the fiscal year ended
          June 30, 1998;

                    (B) as soon as available, but in any event within forty-five
          (45) days after the end of each fiscal  quarter,  internally  prepared
          financial  statements of the Company each prepared in accordance  with
          GAAP and  jobs-in-progress  reports for said period and prior periods;
          provided,  however, that the Company shall have until January 31, 1999
          to deliver  the  financial  statements  for the fiscal  quarter  ended
          September 30, 1998;

                    (C)  within  a  reasonable  time  after  a  written  request
          therefor,  such other  financial data or information as the Holder may
          reasonably request from time to time;

                    (D) at the same time as it delivers the financial statements
          required  under the provisions of  subsections  (A) and (B) hereof,  a

<PAGE>

          certificate  signed  by the  president  or  the  chief  financial,  or
          accounting,  officer of the  Company,  to the effect  that no Event of
          Default  hereunder or material  default  under any other  agreement to
          which the Company is a party or by which it is bound,  or by which any
          of its properties or assets may be affected,  and no event which, with
          the giving of notice or the lapse of time, or both,  would  constitute
          such an Event of Default, has occurred;

                    (E) on a monthly  basis,  no later than the tenth (10th) day
          after each such month,  backlog reports and accounts receivable agings
          of the Company;

               (vii) permit the Holder to make or cause to be made,  inspections
     and  audits of any books,  records  and  papers of the  Company  and of any
     parent or  subsidiary  thereof and to make  extracts  therefrom at all such
     reasonable times and as often as the Holder may reasonably require;

               (viii)  immediately  give  notice to the Holder  that an Event of
     Default has occurred or that an event  which,  with the giving of notice or
     lapse of time, or both, would constitute an Event of Default,  has occurred
     and  specifying the action which the Company has taken and proposes to take
     with respect thereto.

          (b) Financial Covenant: At the end of each fiscal quarter, the Company
shall maintain a Tangible Net Worth of (-3,042,322) or greater (as calculated in
accordance with GAAP).  For purposes hereof  "Tangible Net Worth" shall mean, at
any date,  (i) the net book value of assets (other than patents,  patent rights,
trademarks, trade names, franchises, copyrights, licenses, permits, goodwill and
other  intangible  assets  classified as such in accordance with GAAP) after all
appropriate adjustments in accordance with GAAP (including,  without limitation,
reserves for doubtful receivables, obsolescence,  depreciation and amortization)
plus (ii)  subordinated  indebtedness,  in each case computed in accordance with
GAAP.

          (c) Negative Covenants:  The Company will not, and will not permit any
subsidiary to:

               (i) create,  incur,  assume or suffer to exist any  liability for
     borrowed money,  except (A) indebtedness to the Bank or any other financial
     institution   constituting   "Senior  Debt"  hereunder;   (B)  indebtedness
     outstanding  on  the  date  hereof;  (C)  indebtedness  represented  by the
     Debentures  (and  any  replacement  Debenture  or  Debentures  issued  upon
     transfer or exchange of the Debentures);  (D)  indebtedness  represented by
     the  Class A  Accrued  Interest  Debentures  (and any  replacement  Class A
     Accrued Interest  Debenture or Class A Accrued Interest  Debentures  issued
     upon transfer or exchange of the Class A Accrued Interest Debentures);  (E)
     indebtedness  represented by the Class B Accrued  Interest  Debentures (and
     any  replacement  Class B  Accrued  Interest  Debenture  or Class B Accrued
     Interest Debentures issued upon transfer or exchange of the Class B Accrued
     Interest  Debentures);  and  (F)  other  indebtedness  for  borrowed  money
     (whether or not  constituting  a refinancing of existing  indebtedness)  so
     long  as (x)  such  indebtedness  is not  secured  by  collateral  securing
     repayment of the  Debentures,  (y) such  indebtedness  contains  provisions

<PAGE>

     reasonably  satisfactory to the Majority Holders  subordinating the payment
     of principal  and interest  thereon to the prior  payment of principal  and
     interest on the Debentures,  and (z) the incurrence of which will not cause
     an Event of Default,  or an event which with notice or the lapse of time or
     both  would  constitute  an  Event  of  Default,  hereunder  (collectively,
     "Permitted Indebtedness");

               (ii)  create,  incur,  assume or suffer to exist,  any  mortgage,
     pledge,  lien or encumbrance of or upon or security interest in, any of its
     property or assets now owned or hereafter  acquired  except (A)  mortgages,
     liens, pledges and security interests securing Permitted Indebtedness;  (B)
     other  liens,  charges and  encumbrances  incidental  to the conduct of its
     business or the ownership of its property and assets which are not incurred
     in  connection  with the borrowing of money or the obtaining of advances or
     credit and which do not materially  impair the use thereof in the operation
     of its business;  (C) liens for taxes or other  governmental  charges which
     are not delinquent or which are being contested in good faith and for which
     a reserve shall have been  established  in accordance  with GAAP; (D) liens
     granted to secure  purchase  money  financing of  equipment,  provided such
     liens are  limited  to the  equipment  financed;  and (E) liens  granted to
     refinance  unencumbered  equipment  provided  such liens are limited to the
     equipment  refinanced  and the incurrence of which will not cause a default
     hereunder or in any Senior Debt;

               (iii) assume,  endorse,  be or become liable for or guarantee the
     obligations  of any other person  except by the  endorsement  of negotiable
     instruments for deposit or collection in the ordinary course of business;

               (iv)  (A)  terminate  any  pension  plan so as to  result  in any
     material liability to The Pension Benefit Guaranty Corporation  established
     pursuant to Subtitle A of Title IV of ERISA (the "PBGC"),  (B) engage in or
     permit any person to engage in any "prohibited  transaction" (as defined in
     Section 406 of ERISA or Section 4975 of the Internal  Revenue Code of 1986,
     as amended)  involving  any pension plan which would subject the Company to
     any material tax, penalty or other liability,  (C) incur or suffer to exist
     any material "accumulated funding deficiency" (as defined in Section 302 of
     ERISA), whether or not waived,  involving any pension plan, or (D) allow or
     suffer to exist any event or condition,  which  presents a material risk of
     incurring a material  liability to the PBGC by reason of termination of any
     pension plan;

               (v)  amend,  supplement  or  modify  the  terms  of  the  Subject
     Securities  or increase the  outstanding  amount of any Subject  Securities
     (excluding awards granted under the Plan or under an incentive compensation
     plan or arrangement  approved by the Company's Board of Directors or by the
     Compensation  Committee of the Company's  Board of  Directors)  without the
     prior consent of the Majority Holders;

               (vi) enter into any merger or  consolidation  unless the  Company
     shall be the  surviving  entity in any such  merger or  consolidation,  and
     after  giving  effect to the  transaction  no Event of Default and no event
     which with the giving of notice or passage of time or both would constitute

<PAGE>

     an Event of Default  shall have occurred and be  continuing,  or liquidate,
     wind-up or dissolve itself or sell,  transfer or lease or otherwise dispose
     of all or any substantial part of its assets;

               (vii) lend or advance  money,  credit or property to or invest in
     (by  capital   contribution,   loan,   purchase  or  otherwise)  any  firm,
     corporation,  or other  person  except  (A)  investments  in United  States
     Government  obligations and certificates of deposit of any bank institution
     with  combined  capital  and  surplus of at least  $200,000,000,  (B) trade
     credit,  (C) security  deposits,  or acquire or  otherwise  cause any other
     entity to become a  subsidiary  of the  Company  (as used  herein  the term
     "subsidiary"   means  any  corporation  or  other   organization,   whether
     incorporated  or  unincorporated,   of  which  the  Company  or  any  other
     subsidiary  of the  Company  beneficially  owns a majority of the voting or
     economic interests), and (D) loans outstanding on the date hereof;

               (viii) declare or pay any dividends or  distributions  on account
     of its capital stock or purchase,  redeem,  retire or otherwise acquire any
     of its capital stock or any securities convertible into,  exchangeable for,
     or giving any person the right to acquire or otherwise  subscribe  for, any
     shares of the Company's capital stock;  provided,  however, that so long as
     no Event of Default or event which, with the giving of notice, the lapse of
     time, or both would  constitute an Event of Default  hereunder has occurred
     and is continuing,  the Company may pay regular quarterly  dividends on the
     Preferred Stock in accordance with the terms thereof; or

               (ix)  engage in any  transaction  with any  person or entity  who
     directly or indirectly,  through one or more intermediaries,  controls,  is
     controlled   by,  or  is  under  common   control  with,  the  Company  (an
     "Affiliate"),  other  than  director  and  compensation  arrangements  with
     Affiliates  serving as officers and/or directors of the Company approved by
     the  Company's  Board  of  Directors  and  other  than   transactions  with
     Affiliates  entered into in the ordinary  course of business on terms which
     are at least as favorable to the Company as those  available from unrelated
     third parties.  As used herein,  the term "control"  means the  possession,
     directly or  indirectly,  of the power to direct or cause the  direction of
     the management and policies of the Company,  whether  through the ownership
     of voting securities,  by contract or otherwise, and the terms "controlled"
     and "controlling" have meanings correlative thereto.

          8.   Events of Default.

               (a) Definition.  For the purposes of this Debenture,  an Event of
Default hereunder will be deemed to have occurred if:

                    (i) the Company  fails to pay the  principal  amount of this
          Debenture when due (whether upon the Due Date,  upon  acceleration  or
          otherwise),  whether or not such payment is  prohibited by paragraph 4
          hereof;

<PAGE>

                    (ii) the  Company  fails  to pay any  interest,  premium  or
          penalty on this  Debenture when due and such failure has continued for
          a period of ten (10) days;

                    (iii) the Company fails to perform or observe the provisions
          set forth in Paragraphs 7(b) or 7(c) hereof;

                    (iv) the Company  fails to perform or observe any  provision
          contained in this Debenture (other than those specifically  covered by
          the other  provisions of this paragraph  8(a)) and, if such failure is
          capable of being cured, such failure continues for a period of 30 days
          after the Company's receipt of written notice thereof;

                    (v) the Company shall have failed to pay when due any amount
          due and owing under any indebtedness of the Company for borrowed money
          or any other  default or event of default  shall  have  occurred  (and
          shall have continued  beyond the  expiration of any  applicable  grace
          period) under any indebtedness of the Company for borrowed money which
          would permit the holder thereof to accelerate the maturity  thereof or
          there shall have been an  acceleration  of the stated  maturity of any
          indebtedness of the Company for borrowed money;

                    (vi) the  Company  makes an  assignment  for the  benefit of
          creditors  or  admits  in  writing  its  inability  to pay  its  debts
          generally  as they  become  due;  or an order,  judgment  or decree is
          entered  adjudicating  the Company as bankrupt  or  insolvent;  or any
          order for  relief  with  respect to the  Company is entered  under the
          Federal  Bankruptcy  Code; or the Company  petitions or applies to any
          tribunal  for the  appointment  of a custodian,  trustee,  receiver or
          liquidator of the Company or of any substantial  part of the assets of
          the Company, or commences any proceeding relating to the Company under
          any bankruptcy, reorganization,  arrangement, insolvency, readjustment
          of  debt,   dissolution  or  liquidation   law  of  any   jurisdiction
          ("Insolvency   Event  or   Proceeding");   or  any  such  petition  or
          application is filed, or any such proceeding is commenced, against the
          Company and either (y) the Company by any act  indicates  its approval
          thereof, consents thereto or acquiescence therein or (z) such petition
          application or proceeding is not dismissed within 60 days;

                    (vii) a final  judgment  which in the  aggregate  with other
          outstanding final judgments against the Company exceeds $250,000 shall
          be  rendered  against  the  Company  and  within 90 days  after  entry
          thereof,  such judgment is not discharged or execution  thereof stayed
          pending  appeal,  or within 90 days after the expiration of such stay,
          such judgment is not discharged; or

                    (viii) any representation or warranty made by the Company in
          the Purchase Agreement, dated October 21, 1998 between the Company and
          the  original  Holder of this  Debenture or any other  certificate  or
          instrument delivered in connection therewith shall have been untrue in
          any material respect when made.

<PAGE>

          (b)  Consequences of Events of Default.

                    (i) If any Event of Default  (other than the type  described
          in subparagraph 8(a)(vi) above) has occurred, the Holder or Holders of
          Debentures  representing a majority of the aggregate  principal amount
          of Debentures then outstanding (the "Majority Holders") may demand (by
          written notice delivered to the Company)  immediate  payment of all or
          any portion of the outstanding principal amount of the Debentures owed
          by such Holder or Holders.  If such Majority  Holders demand immediate
          payment of all or any portion of such Holder's or Holders' Debentures,
          the Company  will,  to the extent  permitted  under the  provisions of
          paragraph  4 hereof,  immediately  pay to such  Holder or Holders  the
          principal amount of the Debentures  requested to be paid (plus accrued
          interest  hereon).  If an Event of  Default of the type  described  in
          subparagraph 8(a)(vi) above has occurred,  then all of the outstanding
          principal amount of the Debentures shall  automatically be immediately
          due and  payable  without any action on the part of any Holders of the
          Debentures.

                    (ii) If an Event of Default has occurred, each Holder of the
          Debentures  will also have any other rights which such Holder may have
          pursuant  to  applicable  law, in each case  provided  such rights are
          consistent with the provisions of paragraph 4 hereof.

          9.  Amendment  and  Waiver.  Except as  otherwise  expressly  provided
herein,  the  provisions  of this  Debenture may be a mended and the Company may
take any action herein prohibited, or omit to perform any act herein required to
be performed by it, only if the Company has obtained the written  consent of the
Majority  Holders,  provided,  however,  neither the interest  rate or principal
amounts payable under the  Debentures,  the dates on which interest or principal
under  the  Debentures  is due  nor the  obligations  to  make  payments  on the
Debentures  on a pro rata  basis  shall be  amended  without  the prior  written
consent of each Holder affected thereby, and further provided, however, that any
amendment  or waiver  which  might in any way  adversely  affect the  holders of
Senior Debt,  including,  but not limited to, any amendment or waiver  affecting
the  provisions  of  paragraph  4 or this  paragraph  9 shall  require the prior
written  consent of each holder of Senior Debt. Any amendment or waiver effected
in  accordance  with this  paragraph 9 shall be binding upon each Holder of this
Debenture and each future Holder of this Debenture.

          10. Cancellation. After all principal and accrued interest at any time
owed on this Debenture has been paid in full, this Debenture will be surrendered
to the Company for cancellation and will not be reissued.

          11.  Place of Payment.  Payments of  principal  and interest are to be
delivered to the Holder at the office of the Company, 50 Orville Drive, Bohemia,
New York  11716,  or to such  other  address or to the  attention  of such other
Person as specified by prior written notice to the Company.

<PAGE>

          12. Waiver of  Presentment,  Demand and Dishonor.  The Company  hereby
waives presentment for payment,  protest,  demand, notice of protest,  notice of
non-payment  and  diligence  with  respect  to this  Debenture,  and  waives and
renounces  all  rights to the  benefit  of any  statute  of  limitations  or any
moratorium,  appraisement, exemption or homestead now provided or that hereafter
may be provided by any federal or applicable  state  statute,  including but not
limited to exemptions  provided by or allowed under the Federal Bankruptcy Code,
both as to  itself  and as to all of its  property,  whether  real or  personal,
against the  enforcement  and  collection of the  obligations  evidenced by this
Debenture and any and all extensions, renewals and modifications hereof.

          No failure on the part of the Holder hereof or of any other Debentures
to exercise any right or remedy  hereunder with respect to the Company,  whether
before or after the happening of an Event of Default,  shall constitute a waiver
of any future  Event of Default or of any other Event of Default.  No failure to
accelerate  the debt of the  Company  evidenced  hereby by reason of an Event of
Default  or  indulgence  granted  from time to time shall be  construed  to be a
waiver of the right to insist upon prompt payment thereafter; or shall be deemed
to be a novation of this  Debenture or a  reinstatement  of such debt  evidenced
hereby or a waiver of such  right of  acceleration  or any  other  right,  or be
construed  so as to  preclude  the  exercise  of any right the  Holder may have,
whether by the laws of the state  governing  this  Debenture,  by  agreement  or
otherwise; and the Company hereby expressly waives the benefit of any statute or
rule of law or equity  that would  produce a result  contrary  to or in conflict
with the foregoing.

          13.  Usury.  The Holder and the Company  intend  that the  obligations
evidenced by this Debenture  conform  strictly to the applicable usury laws from
time to time in force.  All  agreements  between  the  Company  and the  Holder,
whether now  existing or hereafter  arising and whether oral or written,  hereby
are expressly limited so that in no contingency or event whatsoever,  whether by
acceleration of maturity hereof or otherwise, shall the amount paid or agreed to
be paid to the  Holder,  or  collected  by the  Holder,  by or on  behalf of the
Company for the use,  forbearance  or detention of the money to be loaned to the
Company  hereunder  or  otherwise,  or for the  payment  or  performance  of any
covenant or obligation  contained herein of the Company to the Holder, or in any
other document evidencing, securing or pertaining to such indebtedness evidenced
hereby,  exceed the maximum amount  permissible  under  applicable usury law. If
under any  circumstances  whatsoever  fulfillment of any provision hereof or any
other document,  at the time  performance of such provisions shall be due, shall
involve  transcending the limit of validity prescribed by law, then, ipso facto,
the  obligation to be fulfilled  shall be reduced to the limit of such validity;
and if under any  circumstances  the Holder ever shall receive from or on behalf
of the Company an amount deemed interest,  by applicable law, which would exceed
the highest  lawful  rate,  such amount that would be excessive  interest  under
applicable  usury  laws  shall be  applied  to the  reduction  of the  Company's
principal amount owing hereunder and not to the payment of interest,  or if such
excessive  interest  exceeds  the  unpaid  balance of  principal  and such other
indebtedness,  the excess shall be deemed to have been a payment made by mistake
and shall be refunded to the Company or to any other person  making such payment
on the Company's behalf.

<PAGE>

          14. Governing Law. The validity,  construction and  interpretation  of
this  Debenture  will  be  governed  by the  internal  laws,  but not the law of
conflicts and choices of law, of the State of New York.

          IN WITNESS WHEREOF,  the Company has executed and delivered this Class
C 13% Convertible Senior Subordinated Debenture this 21st day of October, 1998.

                                            LOGIMETRICS, INC.



                                            By:  __________________________
                                                 Name:   Norman M. Phipps
                                                 Title:  Chief Operating Officer


<PAGE>


                                    EXHIBIT A

                               ELECTION TO CONVERT


                  (All capitalized terms used and not otherwise
                     defined herein shall have the meanings
             assigned to them in the Class C 13% Convertible Senior
                            Subordinated Debentures)


LogiMetrics, Inc.
50 Orville Drive
Bohemia, New York 11716

TO WHOM IT MAY CONCERN:

          The  undersigned   registered  owner  of  the  attached  Class  C  13%
Convertible  Senior  Subordinated  Debenture  hereby  irrevocably  exercises the
option to convert  such  Debenture  into Common  Stock of  LogiMetrics,  Inc. in
accordance  with the terms  thereof,  and directs  that any shares  issuable and
deliverable  upon the  conversion  be issued in the name of and delivered to the
undersigned.



                            ______________________________________________
                            [Name of Debentureholder]


Dated:  _____________, 199__