NOTE


                                                                    July 7, 1998


      FOR VALUE RECEIVED,  SMK GROUP LLC, a Delaware limited  liability  company
(the  "Maker"),  promises  to pay to the  order  of  THERMOTREX  CORPORATION,  a
Delaware  corporation  ("Payee"),  at its address at 10455 Pacific Center Court,
San Diego, CA 92121-4339,  or at such other place as Payee may from time to time
designate in writing, the principal sum of THREE MILLION DOLLARS ($3,000,000) or
such  lesser  amount  as shall be shown on the  records  of Payee as the  unpaid
principal  balance of this Note,  together with interest thereon at the rate set
forth  hereinbelow,  all on the dates set  forth  hereinbelow  and all in lawful
money of the United States of America,  and in  accordance  with the other terms
and conditions described below.

        1.    Payment.

             (a) Interest.  Maker  promises  to  pay  interest  on  the  unpaid
principal balance of this Note at an annual rate equal to the Applicable Federal
Rate (as  defined  in  regulations  to the  Internal  Revenue  Code of 1986,  as
amended) on the date the  principal  sum due  hereunder is disbursed to Maker by
Payee. Accrued interest shall be payable quarterly during the term hereof on the
first day of the months of July, October,  January and April until the principal
amount of, and all accrued interest on, this Note have been paid in full.

             (b) Principal.  Maker promises to pay no less than one half of the
outstanding  principal  balance  due under this Note on or before  July 7, 2001,
with the remainder of the outstanding  principal  balance due and payable (along
with all accrued and unpaid interest due thereon) on July 7, 2002.

       2.   Interest  Computation.  Interest shall be computed on the basis of
a 360-day year for the actual  number of days elapsed (365 or 366/360,  as the
case may be).

       3.   Late Charges. Maker shall pay to Payee a late charge for any payment
of  principal  and/or  interest  received by Payee  fifteen days after it is due
hereunder in an amount equal to five percent (5.0%) of any overdue amount.

       4.   Application of Payments.  All payments shall be applied first to the
payment in full of any costs  incurred  in the  collection  of any sum due under
this Note,  including (without limitation)  reasonable  attorneys' fees, then to
the payment in full of any late charges, then to the payment in full of accrued,
unpaid interest and finally to the reduction of the unpaid principal  balance of
this Note.


       5.   Security.  This Note is secured,  and payment hereof is assured,  by
that certain Pledge and Security Agreement dated of even date herewith,  granted
to Payee by Maker by which  Maker has pledged as  security  for its  obligations
hereunder the Collateral secured thereby.

       6.    Event  of  Default.  It shall be  considered  an Event of  Default
hereunder upon:

             (a)  the  occurrence  of an Event of  Default  under the Pledge and
Security  Agreement  which shall  continue  uncured  within the cure periods set
forth therein, if any, or unwaived by Payee; or

             (b)  the failure of Maker to pay any sums due and payable hereunder
within ten (10) days after written demand therefor by Payee.

        7.    Rights and Remedies.

              (a) Upon the  occurrence  of an Event of Default  hereunder,  upon
fifteen days written notice to Maker,  all amounts owed  hereunder  shall become
automatically due and payable.

              (b) Payee may exercise any of its rights and remedies set forth in
the Pledge and  Security  Agreement,  and all other  documents  and  instruments
executed pursuant to this Note and the Pledge and Security Agreement.

              (c) The remedies of Payee shall be cumulative and concurrent,  and
may be pursued singly,  successively,  or together, at its sole discretion,  and
may be exercised as often as the occasion  therefor shall occur; and the failure
to exercise  any such right or remedy shall in no event be construed as a waiver
or release thereof.

       8.   Limited  Liability.  The  liability  of Maker  hereunder  is limited
strictly  to the  Collateral  pledged to Payee  under the  Pledge  and  Security
Agreement  and shall not extend in any way to any other  assets or  property  of
Maker, its members or any officers, directors, agents, or trustees thereof.

       9.   Waivers.  Maker waives  presentment for payment,  demand,  notice of
dishonor,  protest,  and notice of protest with regard to this Note, all errors,
defects and imperfections in any proceedings instituted by Payee under the terms
of this Note, or under the Pledge and Security  Agreement,  and all benefit that
might  accrue to Maker by virtue of any  present or future  laws  exempting  any
property or any part of the proceeds arising from any sale of any such property,
from  attachment,  levy, or sale under  execution,  or providing for any stay of
execution, exemption from civil process, or extension of time for payment.

      10.    Construction.  This  Note  shall  be  construed  and  enforced  in
accordance   with  the  domestic,   internal  law  of  the   Commonwealth   of
Massachusetts.

      11.   Severability.   Any  provision  contained  in  this  Note  which  is
prohibited or unenforceable in any jurisdiction  shall, as to such jurisdiction,
be ineffective to the extent of such  prohibition  or  unenforceability  without
invalidating  the  remaining  provisions  hereof,  and any such  prohibition  or
unenforceability   in  any   jurisdiction   shall  not   invalidate   or  render
unenforceable such provision in any other jurisdiction.

      12.   Successors,  Heirs and Assigns.  The  provisions  of this Note shall
bind  and  inure  to the  benefit  of  Maker  and  Payee  and  their  respective
successors, heirs, personal representatives and permitted assigns.

      IN WITNESS WHEREOF,  the Maker,  intending to be legally bound hereby, has
caused this Note to be duly executed by its  authorized  members this 7th day of
July, 1998.


                                    SMK GROUP LLC

                                    By:   Its Members


                                          /s/ Lydia Katzoff
                                          Lydia Katzoff


                                          The Stuart Katzoff Trust


                                          By:   /s/ Gerald Katzoff
                                                Gerald Katzoff, Trustee