<PAGE>

                                EXHIBIT 10.6.1


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
 $1,100,000.00        01-28-1999       08-01-2003       462171720      54         5025                        385
------------------------------------------------------------------------------------------------------------------------------------

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
-----------------------------------------------------------------------------------------------------------------------------------
</TABLE>

<TABLE>
<S>          <C>                                       <C>        <C>
Borrower:    Hi-Shear Technology Corporation           Lender:    SOUTHERN CALIFORNIA BANK
             (TIN: 22-2535743)                                    ORANGE COUNTY
             24225 Garnier St.                                    CORPORATE BANKING
             Torrance, CA.  90505                                 P.O. BOX  588
                                                                  LA MIRADA, CA.  90637
====================================================================================================================================
</TABLE>

<TABLE>
<S>                   <C>                <C>            <C>          <C>               <C>
Principal Amount:     $1,100,000.00      Initial Rate:  8.2500%      Date of Note:     January 28, 1999
</TABLE>

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  One Million One Hundred Thousand &
00/100 Dollars ($1,100,000.00) 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 MARCH 1, 1999, AND ALL SUBSEQUENT INTEREST
             PAYMENTS ARE DUE ON THE SAME DAY OF EACH MONTH AFTER THAT. THEN ON
             AUGUST 1, 1999, THE ENTIRE OUTSTANDING PRINCIPAL BALANCE WILL BE
             AMORTIZED OVER A 48 MONTH PERIOD, WITH MONTHLY PRINCIPAL PAYMENTS
             IN THE AMOUNT OF $22,916.67 PLUS ACCRUED INTEREST BEGINNING
             SEPTEMBER 1, 1999. BORROWER'S FINAL PAYMENT WILL BE DUE ON AUGUST
             1, 2003, 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 Index 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 7.750%. The interest rate to be applied to the unpaid principal
balance of this Note will be at a rate of 0.500 percentage
<PAGE>

points over the Index, resulting in an initial rate of 8.250%. 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 any 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 material 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 5.500 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. Lender and Borrower hereby
waive the right to any jury trial in any action, proceeding, or counterclaim
brought by either Lender or Borrower against the other. 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, President; Thomas Mooney, Chief Executive
Officer; and S.Y. Yoshimoto, Controller. Effective August 1, 1999, 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, President             Thomas Mooney, Chief Executive Officer