<PAGE>

                                  EXHIBIT 10.6
                                        

SOUTHERN CALIFORNIA BANK CREDIT FACILITY


                                PROMISSORY NOTE

<TABLE>
<S>               <C>               <C>              <C>            <C>        <C>              <C>           <C>           <C>
   Principal      Loan Date         Maturity         Loan No.       Call       Collateral       Account       Officer      Initials
  $750,000.00     08-06-1997        08-01-2002       407169719       01           0066                          385
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 References in the shaded area are for Lender's use only and do not limit the applicability of this document to any particular loan
 or item
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</TABLE>
Borrower:  Hi-Shear Technology Corporation   Lender:  SOUTHERN CALIFORNIA BANK
           (TIN: 22-2535743)                          LAGUNA HILLS OFFICE
           24225 Garnier St.                          16420 VALLEY VIEW AVENUE
           Torrance, CA.  90505                       P.O. BOX  588
                                                      LA MIRADA, CA.  90637-0588
================================================================================
Principal Amount: $750,000.00 Initial Rate: 9.500%  Date of Note: August 6, 1997

PROMISE TO PAY.  Hi-Shear Technology Corporation ("Borrower") promises to pay to
SOUTHERN CALIFORNIA BANK ("Lender"), or order, in lawful money of the United
States of America, the principal amount of Seven Hundred Fifty Thousand & 00/100
Dollars ($750,000.00) or so much as may be outstanding, together with interest
on the unpaid outstanding principal balance of each advance.  Interest shall be
calculated from the date of each advance until repayment of each advance.

PAYMENT. Borrower will pay this loan on demand, or if no demand is made, in
         accordance with the following payment schedule:

         BORROWER WILL PAY REGULAR MONTHLY PAYMENTS OF ACCRUED UNPAID INTEREST
         BEGINNING SEPTEMBER 1, 1997, AND ALL SUBSEQUENT INTEREST PAYMENTS ARE
         DUE ON THE SAME DAY OF EACH MONTH AFTER THAT.  THEN ON JULY 1, 1998,
         THE ENTIRE OUTSTANDING PRINCIPAL BALANCE WILL BE AMORTIZED EQUALLY OVER
         48 MONTH PERIOD, WITH LEVEL PRINCIPAL PAYMENTS PLUS ACCRUED INTEREST
         DUE MONTHLY BEGINNING AUGUST 1, 1998.  BORROWER'S FINAL PAYMENT WILL BE
         DUE ON AUGUST 1, 2002, AND WILL BE FOR ALL PRINCIPAL AND ACCRUED
         INTEREST NOT YET PAID.

Interest on this Note is computed on a 365/360 simple interest basis; that is,
by applying the ratio of the annual interest rate over a year of 360 days,
multiplied by the outstanding principal balance, multiplied by the actual number
of days the principal balance is outstanding.  Borrower will pay Lender at
Lender's address shown above or at such other place as Lender may designate in
writing.  Unless otherwise agreed or required by applicable law, payments will
be applied first to accrued unpaid interest, then to principal, and any
remaining amount to any unpaid collection costs and late charges.


VARIABLE INTEREST RATE.  The interest rate on this Note is subject to change
from time to time based on changes in an independent index which is the WALL
STREET JOURNAL PRIME RATE (the "Index").  The Index is not necessarily the
lowest rate charged by Lender on its loans.  If the Index becomes unavailable
during the term of this loan, Lender may designate a substitute index after
notice to Borrower.  Lender will tell Borrower the current rate upon Borrower's
request.  Borrower understands that Lender may make loans based on other rates
as well.  The interest rate change will not occur more often than each DAY.  The
index currently is 8.500% per annum.  The interest rate to be applied to the
unpaid principal balance of this Note will be at a rate of 1.000 percentage
<PAGE>
 
point over the Index, resulting in an initial rate of 9.500% per annum.  NOTICE:
Under no circumstances will the interest rate on this Note be more than the
maximum rate allowed by applicable law.

PREPAYMENT; MINIMUM INTEREST CHARGE.  Borrower agrees that all loan fees and
other prepaid finance charges are earned fully as of the date of the loan and
will not be subject to refund upon early payment (whether voluntary or as a
result of default), except as otherwise required by law.  In any event, even
upon full prepayment of this Note, Borrower understands that Lender is entitled
to a minimum interest charge of $250.00.  Other than Borrower's obligation to
pay any minimum interest charge, Borrower may pay without penalty all or a
portion of the amount owed earlier that it is due.  Early payments will not,
unless agreed to by Lender in writing, relieve Borrower of Borrower's obligation
to continue to make payments of accrued unpaid interest.  Rather, they will
reduce the principal balance due.

LATE CHARGE.  If a payment is 10 days or more late, Borrower will be charged
5.000% of the regularly scheduled payment or $5.00 whichever is greater.

DEFAULT.  Borrower will be in default if any of the following happens: (a)
Borrower fails to make payment when due.  (b) Borrower breaks any promise
Borrower has made to Lender, or Borrower fails to comply with or to perform when
due any other term, obligation, covenant, or condition contained in this Note or
any agreement related to this Note, or in any other agreement or loan Borrower
has with Lender.  (c) Borrower defaults under any loan, extension of credit,
security agreement, purchase or sales agreement, or any other agreement, in
favor of any other creditor or person that may materially affect any of
Borrower's property or Borrower's ability to repay this Note or perform
Borrower's obligations under this Note or any of the Related Documents.  (d) Any
representation or statement made or furnished to Lender by Borrower or on
Borrower's behalf is false or misleading in any materiel respect either now or
at the time made or furnished.  (e) Borrower becomes insolvent, a receiver is
appointed for any part of Borrower's property, Borrower makes an assignment for
the benefit of creditors, or any proceeding is commenced either by Borrower or
against Borrower under any bankruptcy or insolvency laws.  (f)  Any creditor
tries to take any of Borrower's property on or in which Lender has a lien or
security interest.  This includes a garnishment of any of Borrower's accounts
with Lender.  (g) Any guarantor dies or any of the other events described in
this default section occurs with respect to any guarantor of this Note.  (h) A
material adverse change occurs in Borrower's financial condition, or Lender
believes the prospect of payment or performance of the indebtedness is impaired.
(I) Lender in good faith deems itself insecure.

LENDER'S RIGHTS.  Upon default, Lender may declare the entire unpaid principal
balance on this Note and all accrued unpaid interest immediately due, without
notice, and then Borrower will pay that amount.  Upon Borrower's failure to pay
all amounts declared due pursuant to this section, including failure to pay upon
final maturity, Lender, at its option, may also, if permitted under applicable
law, increase the variable interest rate on this Note to 6.000 percentage points
over the Index.  Lender may hire or pay someone else to help collect this Note
if Borrower does not pay.  Borrower also will pay Lender that amount.  This
includes, subject to any limits under applicable law, Lender's attorneys' fees
and Lender's legal expenses whether or not there is a lawsuit, including
attorneys' fees and legal expenses for bankruptcy proceedings (including efforts
to modify or vacate any automatic stay or injunction), appeals, and any
anticipated post-judgment collection services.  Borrower also will pay any court
costs, in addition to all other sums provided by law.  This Note has been
delivered to Lender and accepted by Lender in the State of California.  If there
is a lawsuit, Borrower agrees upon Lender's request to submit to the
jurisdiction of the courts of ORANGE County, the State of California.  Subject
to the provisions of arbitration, this Note shall be governed by and construed
in accordance with the laws of the State of California.

DISHONORED ITEM FEE.  Borrower will pay a fee to Lender of $16.00 if Borrower
makes a payment on Borrower's loan and the check or preauthorized charge with
which Borrower pays is later dishonored.

RIGHT OF SETOFF.  Borrower grants to Lender a contractual possessory security
interest in, and hereby assigns, conveys, delivers, pledges, and transfers to
Lender all Borrower's right, title and interest in and to, Borrower's accounts
with Lender (whether check, savings, or some other account), including without
limitation all accounts held jointly with someone else and all accounts Borrower
may open in the future, excluding however all IRA and Keogh accounts, and all
trust accounts for which the grant of a security interest would be prohibited by
law.  Borrower authorizes Lender, to the extent permitted by applicable law, to
charge or setoff all sums owing on this Note against any and all such accounts.
<PAGE>
 
LINE OF CREDIT.  This Note evidences a revolving line of credit.  Advances under
this Note may be requested either orally or in writing by Borrower or as
provided in this paragraph.  Lender may, but need not, require that all oral
request be confirmed in writing.  All communications, instructions, or
directions by telephone or otherwise to Lender are to be directed to Lender's
office shown above.  The following party or parties are authorized as provided
in this paragraph to request advances under the line of credit until Lender
receives from Borrower at Lender's address shown above written notice of
revocation of their authority:  George Trahan, Chief Financial Officer; Thomas
Mooney, President; and S.Y. Yoshimoto, Controller.  Effective July 1, 1998, the
remaining availability under the line shall be terminated and no additional
advances will be allowed.  Borrower agrees to be liable for all sums either:
(a) advanced in accordance with the instructions of an authorized person or (b)
credited to any of Borrower's accounts with Lender.  The unpaid principal
balance owing on this Note at any time may be evidenced by endorsements on this
Note or by Lender's internal records, including daily computer print-outs.
Lender will have no obligation to advance funds under this Note if:  (a)
Borrower or any guarantor is in default under the terms of this Note or any
agreement that Borrower or any guarantor has with Lender, including any
agreement made in connection with the signing of this Note; (b) Borrower or any
guarantor ceases doing business or is insolvent; (c) any guarantor seeks, claims
or otherwise attempts to limit, modify or revoke such guarantor's guarantee of
this Note or any other loan with Lender; (d) Borrower has applied funds provided
pursuant to this Note for purposes other than those authorized by Lender; or (e)
Lender in good faith deems itself insecure under this Note or any other
agreement between Lender and Borrower.

ARBITRATION.  Lender and Borrower agree that all disputes, claims and
controversies between them, whether individual, joint, or class in nature,
arising from this Note or otherwise, including without limitation contract and
tort disputes, shall be arbitrated pursuant to the Rules of the American
Arbitration Association, upon request of either party.  No act to take or
dispose of any collateral securing this Note shall constitute a waiver of this
arbitration agreement or be prohibited by this arbitration agreement.  This
includes, without limitation, obtaining injunctive relief or a temporary
restraining order; invoking a power of sale under any deed of trust or mortgage;
obtaining a writ of attachment or imposition of a receiver; or exercising any
rights relating to personal property, including taking or disposing of such
property with or without judicial process pursuant to Article 9 of the Uniform
Commercial Code.  Any disputes, claims, or controversies concerning the
lawfulness or reasonableness of any act, or exercise of any right, concerning
any collateral securing this Note, including any claim to rescind, reform, or
otherwise modify any agreement relating to the collateral securing this Note,
shall also be arbitrated, provided however that no arbitrator shall have the
right or the power to enjoin or restrain any act of any party.  Lender and
Borrower agree that in the event of an action for judicial foreclosure pursuant
to California Code of Civil procedure Section 726, or any similar provision in
any other state, the commencement of such an action will not constitute a waiver
of the right to arbitrate and the court shall refer to arbitration as much as
such action, including counterclaims, as lawfully may be referred to
arbitration.  Judgment upon any award rendered by any arbitrator may be entered
in any count having jurisdiction.  Nothing in this Note shall preclude any party
from seeking equitable relief from a court of competent jurisdiction.  This
statue of limitations, estoppel, waiver, laches, and similar doctrines which
would otherwise be applicable in an action brought by a party shall be
applicable in any arbitration proceeding, and the commencement of an arbitration
proceeding shall be deemed the commencement of an action for these purposes.
The Federal Arbitration Act shall apply to the construction, interpretation, and
enforcement of this arbitration provision.

GENERAL PROVISIONS.  This Note is payable on demand.  The inclusion of specific
default provisions or rights of Lender shall not preclude Lender's right to
declare payment of this Note on its demand.  Lender may delay or forgo enforcing
any of its right or remedies under this Note without losing them.  Borrower and
any other person who signs, guarantees or endorses this Note, to the extent
allowed by law, waive any applicable statute of limitations, presentment, demand
for payment, protest and notice of dishonor. Upon any change in the terms of
this Note, and unless otherwise expressly stated in writing, no party who signs
this Note, whether as maker, guarantor, accommodation make or endorser, shall be
released from liability.  All such parties agree that Lender may renew or extend
(repeatedly and for any length of time) this loan, or release any party or
guarantor or collateral; or impair, fail to realize upon or perfect Lender's
security interest in the collateral; and take any other action deemed necessary
by Lender without the consent of or notice to anyone.  All such parties also
agree that Lender may modify this loan without consent of or notice to anyone
other than the party with whom the modification is made.
<PAGE>
 
PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF
THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS.  BORROWER AGREES TO
THE TERMS OF THE NOTE AND ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THE NOTE.

BORROWER:

Hi-Shear Technology Corporation

By:  /s/ George W. Trahan                      By:  /s/ Thomas R. Mooney
     --------------------                           --------------------
     George Trahan, Chief Financial Officer         Thomas Mooney, President