Document:

<PAGE>

                                                                   Exhibit 10.21
                                                                   -------------

                                PROMISSORY NOTE

$1,779,050.00                                                     August 6, 1999

          FOR VALUE RECEIVED, THE UNDERSIGNED, SHERBORNE INVESTMENTS
CORPORATION, a Delaware corporation (the "Borrower"), HEREBY PROMISES TO PAY to
the order of AMPEX CORPORATION, a Delaware corporation ("Payee"), on January 24,
2005, the principal sum of One Million Seven Hundred Seventy-Nine Thousand Fifty
Dollars ($1,779,050.00), together with interest on the principal amount hereof
from time to time outstanding at the rate of 7.96% per annum.  Accrued interest
on this Note shall be payable on each December 31 and on the date of each
payment hereof until this Note is paid in full.

          The Borrower shall have the right, at any time, to prepay all or any
part of the outstanding principal amount without premium or penalty.  In
addition, Borrower may, in lieu of making any principal or interest payment of
this Note in cash, tender to Payee shares of the Class A Common Stock, par value
$0.01 per share, of Ampex Corporation (the "Class A Shares") having an aggregate
value equal to all or any portion of such principal or interest payment;
provided, however, that for such purposes each of the Class A Shares so tendered
shall be deemed to have a value on any such payment date equal to its fair
market value on such date.

          The occurrence of any one of the following shall constitute an Event
of Default hereunder:

          (a)  The Borrower shall default in the payment of the principal of or
accrued interest on this Note when due and such default shall continue for a
period of three (3) days after notice from the holder of this Note;

          (b)  The Borrower shall default in the performance of any other term
of this Note and such default shall continue for 30 days after notice from the
holder of this Note; or

          (c)  The Borrower shall (i) be adjudicated a bankrupt or insolvent; or
file a voluntary petition in bankruptcy; or (ii) any involuntary petition in
bankruptcy shall be filed against the Borrower which shall not have been
discharged within 60 days.

          Upon the occurrence of an Event of Default, and at any time thereafter
while such Event of Default is continuing:

          (a)  the holder of this Note may by written notice to the Borrower
declare all or any part of the unpaid balance of this Note immediately due and
payable, whereupon such unpaid balance or part thereof shall become so due and
payable without presentation, protest or further demand or notice of any kind,
all of which are hereby expressly waived, and the holder of this Note may
proceed to enforce payment of such balance or part thereof in such manner as it
may elect; and
<PAGE>

          (b)  the holder of this Note may proceed to protect and enforce its
rights by suit in equity, action at law and/or other appropriate means and may
exercise any and all rights afforded a secured creditor under the Uniform
Commercial Code, including without limitation, enforcement of rights under the
Pledge Agreement referred to below.

          The Borrower hereby agrees to pay on demand reasonable costs and
expenses, including without limitation reasonable attorneys' fees, incurred or
paid by the holder of this Note in enforcing this Note upon the occurrence of an
Event of Default.

          The Borrower hereby waives presentment, demand, notice, protest and
other demands and notices in connection with the delivery, acceptance, or
enforcement of this Note.

          No delay or omission on the part of holder of this Note in exercising
any right hereunder shall operate as a waiver of such right or any other right
under this Note, and a waiver, delay or omission on any one occasion shall not
be construed as a bar to or waiver of any such right on any future occasion.

          This Note is subject to the terms and conditions set forth in the
Stock Purchase Agreement dated as of February 10, 1995 between the Payee and
Edward J. Bramson, and is secured by a pledge with the Payee of certain
Collateral under the terms of a Pledge Agreement, of even date, between the
Borrower and the Payee.

          All notices hereunder shall be deemed to have been given when
delivered in person or, if mailed, when actually received by the party to whom
addressed.  Such actual receipt shall be presumed if such notice shall be mailed
by registered or certified mail, addressed to any party at its address set forth
below or at any other address notified in writing to the other parties hereto,
and if the sender shall have received back a return receipt.

To the Borrower:    Sherborne Investments Corporation
                    135 East 57/th/ Street, 32/nd/ Floor
                    New York, NY 10022
                    Attention: Mr. Edward J. Bramson

To the Payee:       Ampex Corporation
                    500 Broadway
                    Redwood City, CA 94063
                    Attention: Mr. Craig L. McKibben

       This Note shall be governed by the laws of the State of Delaware.

                                       2
<PAGE>

          IN WITNESS WHEREOF, the undersigned has executed and delivered this
Note as of the date first above written.

                              SHERBORNE INVESTMENTS CORPORATION

                              By: /s/ Edward J. Bramson
                                  ---------------------
                                  Edward J. Bramson
                                  President

                                       3<PAGE>

                                                                   Exhibit 10.22
                                                                   -------------

                                PROMISSORY NOTE

$2,200,000                                                    September 17, 1998

          FOR VALUE RECEIVED, THE UNDERSIGNED, SH SECURITIES CO., LLC, a New
York limited liability company (the "Borrower") HEREBY PROMISES TO PAY to the
order of AMPEX CORPORATION, a Delaware corporation ("Payee"), on October 15,
2008, the principal sum of Two Million Two Hundred Thousand Dollars
($2,200,000), together with interest on the principal amount hereof from time to
time outstanding at the rate of 5.74% per annum.  Accrued interest on this Note
shall be payable on each October 15 and on the date of each payment of the
principal hereof until this Note is paid in full.

          This Note is subject to the provisions of an agreement, dated
September 11, 1998, between the Payee and the Borrower, which provides, among
other things, that payment of the principal of, and accrued interest on, this
Note is subject to reduction or forgiveness, in whole or in part, in certain
circumstances, which provisions are incorporated herein by reference as if fully
set forth in this Note.  The Payee agrees that it will not sell, assign,
transfer, pledge, or otherwise dispose of this Note without obtaining the
acknowledgment of the transferee of the provisions of such agreement.

          The Borrower shall have the right, at any time, to prepay all or any
part of the outstanding principal amount without premium or penalty.

          The occurrence of any one of the following shall constitute an Event
of Default hereunder:

          (a) The Borrower shall default in the payment of the principal of or
accrued interest on this Note when due and such default shall continue for a
period of three (3) days after notice from the holder of this Note;
<PAGE>

          (b) The Borrower shall default in the performance of any other term of
this Note and such default shall continue for 30 days after notice from the
holder of this Note; or

          (c) The Borrower shall (i) be adjudicated a bankrupt or insolvent; or
file a voluntary petition in bankruptcy; or (ii) any involuntary petition in
bankruptcy shall be filed against the Borrower which shall not have been
discharged within 60 days.

          Upon the occurrence of an Event of Default, and at any time thereafter
while such Event of Default is continuing:

          (a) the holder of this Note may by written notice to the Borrower
declare all or any part of the unpaid balance of this Note immediately due and
payable, whereupon such unpaid balance or part thereof shall become so due and
payable without presentation, protest or further demand or notice of any kind,
all of which are hereby expressly waived, and the holder of this Note may
proceed to enforce payment of such balance or part thereof in such manner as it
may elect; and

          (b) the holder of this Note may proceed to protect and enforce its
rights by suit in equity, action at law and/or other appropriate means and may
exercise any and all rights afforded a secured creditor under the Uniform
Commercial Code, including without limitation, enforcement of rights under the
Pledge Agreement referred to below.

          The Borrower hereby agrees to pay on demand reasonable costs and
expenses, including without limitation reasonable attorneys' fees, incurred or
paid by the holder of this Note in enforcing this Note upon the occurrence of an
Event of Default.

          The Borrower hereby waives presentment, demand, notice, protest and
other demands and notices in connection with the delivery, acceptance or
enforcement of this Note.

          No delay or omission on the part of the holder of this Note in
exercising any right hereunder shall operate as a waiver of such right or of any
other right under this Note, and a waiver, delay or omission on any one occasion
shall not be construed as a bar to or waiver of any such right on any future
occasion.
<PAGE>

          This Note is secured by a pledge with the Payee of certain Collateral
under the terms of a Pledge Agreement, of even date, between the Borrower and
the Payee.

          No director, officer, employee, member, manager or stockholder, as
such, of the Borrower shall have any liability to the holder of this Note for
any obligations of the Borrower under this Note or for any claims based on or in
respect of such obligations.

          All notices hereunder shall be deemed to have been given when
delivered in person or, if mailed, when actually received by the party to whom
addressed. Such actual receipt shall be presumed if such notice shall be mailed
by registered or certified mail, addressed to any party at its address set forth
below or at any other address notified in writing to the other parties hereto,
and if the sender shall have received back a return receipt.

To the Borrower:         135 East 57th Street
                         New York, NY  10022

To the Payee:            500 Broadway
                         Redwood City, CA  94063
                         Attention: Chief Financial Officer

          This Note shall be governed by the laws of the State of New York.

                         SH SECURITIES CO., LLC

                         By /s/ Edward J. Bramson
                            ----------------------
                            Title: Managing Member

                                      -3-
<PAGE>

                                                              September 17, 1998

Edward J. Bramson
Chairman
Ampex Corporation
500 Broadway
Redwood City, CA 94063

Dear Mr. Bramson:

     We refer to the Stock Purchase Agreement, dated as of October 22, 1996 (the
"Agreement"), between Ampex Corporation (the "Corporation") and you, pursuant to
which the Corporation sold to your designee, SH Securities Co., LLC, a New York
limited liability company ("SHS"), of which you are the sole managing member,
400,000 shares of the Class A Common Stock (the "Shares") of the Corporation at
a purchase price of $6.875 per Share, in exchange for cash in the amount of
$550,000 and a secured promissory note (the "Note") in the amount of $2,200,000
executed by SHS.

     On August 27, 1998, the Board of Directors of the Corporation unanimously
authorized the Corporation to modify the terms of the Note in certain respects.
In accordance with the terms approved by the Board, the Corporation hereby
agrees with you and SHS as follows:

     1. The final maturity date of the Note shall be extended to October 15,
2008, and subject to paragraph 2 below, the principal amount of the Note shall
be reduced in ten (10) equal annual installments of $176,000 each to $440,000,
commencing on October 15, 1998 and continuing until the final maturity date,
whereupon the remaining unpaid balance of the Note shall be due and payable.  In
addition, if during any ten (10) consecutive trading day period, the average
closing price of the Class A Common Stock on the American Stock Exchange shall
equal or exceed $7.00 per share, the unpaid principal balance of the Note shall
thereupon be reduced to $440,000. Interest on the modified Note shall be payable
at the rate of 5.74% per annum.  Subject to paragraph 2 below, accrued interest
on the unpaid principal amount of the Note due on each October 15 during the
term of the Note shall be forgiven on each such interest payment date. Upon your
execution and delivery of this agreement, the existing Note shall be exchanged
for a new Note reflecting such modifications in substantially the form attached
hereto.
<PAGE>

Edward J. Bramson
September 17, 1998
Page 2

     2. If you shall voluntarily resign as an officer and director of the
Corporation or shall be discharged for "Cause" (as defined in the Agreement)
prior to the final maturity date of the Note, no further reductions of the
principal of, or forgiveness of accrued interest on, the Note shall take effect
pursuant to this agreement after the effective date of such resignation or
discharge.

     3. The Corporation further agrees that, in the event of a Change of
Control (as defined below) of the Corporation during the term of the Note, the
Corporation will give you prompt written notice of such event and will afford
you the opportunity (in addition to your prepayment rights under the Note, which
shall not be affected by this agreement), which shall remain open for a period
of thirty (30) days after delivery of such notice to you, to surrender the
Shares then securing the Note under the Pledge Agreement entered into by you
pursuant to the Agreements in exchange for a full release of and cancellation of
any claims by the Corporation for repayment of such indebtedness and return of
such Note and any cash payments theretofore made by you in payment for the
Shares (without interest). In order to elect such option you shall deliver to
the Corporation, within such thirty day period, a written notice of your
election.  Such election shall be effective with respect to all (but not less
than all) the Shares then securing the Note.  If you do not deliver such written
notice within such thirty day period, the existing arrangements shall remain in
effect.

     For purposes of this Agreement, the term "Change of Control" shall mean the
occurrence of any of the following events: (i) any  "person" or "group" (as such
terms are used in Sections 13(d) and 14(d) of the Securities Exchange Act of
1934, as amended (the "Act"), other than you or your Affiliates (as defined in
the Rules of the Securities and Exchange Commission under the Act), becomes or
publicly commences a tender offer seeking to become the "beneficial owner" (as
defined in Rules 13d-3 and 13d-5 under the Act, except that a person or group
will be deemed to have "beneficial ownership" of all securities that such person
or group has the right to acquire, whether such right is exercisable immediately
or only after the passage of time or the occurrence of a specified event),
directly or indirectly, of 30% or more of the outstanding Common Stock of the
Corporation; (ii) the Corporation consolidates with, or merges with or into
another person, pursuant to a transaction in which the outstanding voting stock
of the Corporation is converted into or exchanged for cash, securities or other
property; or (iii) the Corporation enters into any agreement contemplating any
of the foregoing transactions; excluding, however, from (ii) and (iii) any
transaction or agreement with a subsidiary of the Corporation or an entity
controlled by you or your Affiliates.
<PAGE>

Edward J. Bramson
September 17, 1998
Page 2

     4. All other terms and conditions of the Agreement and the Note shall
remain in full force and effect.

     If the foregoing correctly sets forth our agreement, please sign the
enclosed copy of this letter and return it to the undersigned, whereupon it will
become a binding agreement between us.

                                          Very truly yours,

                                          AMPEX CORPORATION

                                          By /s/ Craig L. McKibben
                                            -----------------------------
                                            Vice President

Accepted and agreed as of
the date first set forth above.

/s/ Edward J. Bramson
-------------------------------
Edward J. Bramson, individually
and as Managing Member of SHS

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00023-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00023-of-00352.parquet"}]]