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                                                                    EXHIBIT 10.1

               FOURTH AMENDMENT TO CREDIT AND SECURITY AGREEMENT
                        AND AMENDMENT OF DEFAULT LETTER


     This Fourth Amendment to Credit And Security Agreement and Amendment of
Default Letter, dated as of April 21, 2000, is made by and between P. G. DESIGN
ELECTRONICS, INC., a Delaware corporation (the "Borrower"), and WELLS FARGO
BUSINESS CREDIT, INC., a Minnesota corporation formerly known as Norwest
Business Credit, Inc. (the "Lender").

                                R E C I T A L S:


     The Borrower and the Lender have entered into a Credit and Security
Agreement dated as of December 31, 1998, as amended (the "Credit Agreement").
Capitalized terms used in these recitals have the meanings given to them in the
Credit Agreement unless otherwise specified.

     Pursuant to a letter dated January 27, 2000 (the "Default Letter"), the
Lender demanded payment of the Obligations by no later than May 1, 2000. The
Borrower has requested that the Lender agree to an extension of the time for
payment of the Obligations in full, which the Lender is willing to do pursuant
to the terms and conditions set forth herein.

     NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements herein contained, it is agreed as follows:

     1.  Defined Terms.  Capitalized terms used in this Amendment which are
         -------------
defined in the Credit Agreement shall have the same meanings as defined therein,
unless otherwise defined herein.

     2.  Amendment to Section 2.3.  Section 2.3 of the Credit Agreement is
         ------------------------
amended to read as follows:

          Section 2.3.  Payment of Term Note.  The outstanding principal balance
                        --------------------
     of the Term Note shall be due and payable as follows:

          (a) Beginning on February 1, 1999, and on the first day of each month
     thereafter through May 1, 2000, in equal monthly installments of Seventy
     Five Thousand Dollars ($75,000) each; and

          (b) Beginning on May 8, 2000, and on the first Banking Day of each
     week thereafter, in equal weekly installments of Twenty Five Thousand
     Dollars ($25,000) each; and

          (c) On the Termination Date, the entire unpaid principal balance of
     the Term Note, and all unpaid interest accrued thereon, shall in any event
     be due and
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     payable.

     3.  Extension of Final Date for Payment.  Notwithstanding the terms of the
         -----------------------------------
Default Letter, the Lender hereby agrees to extend the time for payment in full
of the Obligations to August 1, 2000.

     4.  Accommodation Fee.  In consideration of the Lender's execution of this
         -----------------
Amendment, the Borrower hereby agrees to pay to the Lender a fully earned,
nonrefundable fee in the amount of One Hundred Thousand Dollars ($100,000). In
consideration of the payment of such fee, the Lender agrees to waive further
payments of the Ten Thousand Dollar ($10,000) monthly accommodation fee required
pursuant to the Default Letter.

     5.  No Other Changes.  Except as explicitly amended by this Amendment, all
         ----------------
of the terms and conditions of both the Credit Agreement and the Default Letter
shall remain in full force and effect and shall apply to any Advance or Letter
of Credit thereunder.

     6.  Conditions Precedent.  This Amendment shall be effective when the
         --------------------
Lender shall have received an executed original hereof, together with each of
the following, each in substance and form acceptable to the Lender in its sole
discretion:

          (a) A Certificate of the Secretary of the Borrower certifying as to
     (i) the resolutions of the board of directors of the Borrower approving the
     execution and delivery of this Amendment, (ii) the fact that the articles
     of incorporation and bylaws of the Borrower, which were certified and
     delivered to the Lender pursuant to the Certificate of Authority of the
     Borrower's secretary or assistant secretary dated as of December 31, 1998
     continue in full force and effect and have not been amended or otherwise
     modified except as set forth in the Certificate to be delivered, and (iii)
     setting forth the sample signatures of each of the officers and agents of
     the Borrower authorized to execute and deliver this Amendment and all other
     documents, agreements and certificates on behalf of the Borrower.


          (b)  The Acknowledgment and Agreement of Guarantors set forth at the
     end of this Amendment, duly executed by each Guarantor.

          (c) Such other matters as the Lender may require.

     7.  Representations and Warranties.  The Borrower hereby represents and
         ------------------------------
warrants to the Lender as follows:

          (a) The Borrower has all requisite power and authority to execute this
     Amendment and to perform all of its obligations hereunder, and this
     Amendment has been duly executed and delivered by the Borrower and
     constitutes the legal, valid and binding obligation of the Borrower,
     enforceable in accordance with its terms.

          (b) The execution, delivery and performance by the Borrower of this
     Amendment have been duly authorized by all necessary corporate action and
     do not

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     (i) require any authorization, consent or approval by any governmental
     department, commission, board, bureau, agency or instrumentality, domestic
     or foreign, (ii) violate any provision of any law, rule or regulation or of
     any order, writ, injunction or decree presently in effect, having
     applicability to the Borrower, or the articles of incorporation or by-laws
     of the Borrower, or (iii) result in a breach of or constitute a default
     under any indenture or loan or credit agreement or any other agreement,
     lease or instrument to which the Borrower is a party or by which it or its
     properties may be bound or affected.

          (c) All of the representations and warranties contained in Article V
     of the Credit Agreement are correct on and as of the date hereof as though
     made on and as of such date, except to the extent that such representations
     and warranties relate solely to an earlier date.

     8.  References.  All references in the Credit Agreement to "this Agreement"
         ----------
shall be deemed to refer to the Credit Agreement as amended hereby; and any and
all references in the Security Documents to the Credit Agreement shall be deemed
to refer to the Credit Agreement as amended hereby.

     9.  No Waiver.  The execution of this Amendment and acceptance of any
         ---------
documents related hereto shall not be deemed to be a waiver of any Default or
Event of Default under the Credit Agreement or breach, default or event of
default under any Security Document or other document held by the Lender,
whether or not known to the Lender and whether or not existing on the date of
this Amendment.

     10.  Release.  The Borrower, and each Guarantor by signing the
          -------
Acknowledgment and Agreement of Guarantors set forth below, each hereby
absolutely and unconditionally releases and forever discharges the Lender, and
any and all participants, parent corporations, subsidiary corporations,
affiliated corporations, insurers, indemnitors, successors and assigns thereof,
together with all of the present and former directors, officers, agents and
employees of any of the foregoing, from any and all claims, demands or causes of
action of any kind, nature or description, whether arising in law or equity or
upon contract or tort or under any state or federal law or otherwise, which the
Borrower or such Guarantor has had, now has or has made claim to have against
any such person for or by reason of any act, omission, matter, cause or thing
whatsoever arising from the beginning of time to and including the date of this
Amendment, whether such claims, demands and causes of action are matured or
unmatured or known or unknown.

     11.  Costs and Expenses.  The Borrower hereby reaffirms its agreement under
          ------------------
the Credit Agreement to pay or reimburse the Lender on demand for all costs and
expenses incurred by the Lender in connection with the Credit Agreement, the
Security Documents and all other documents contemplated thereby, including
without limitation all reasonable fees and disbursements of legal counsel.
Without limiting the generality of the foregoing, the Borrower specifically
agrees to pay all fees and disbursements of counsel to the Lender for the
services performed by such counsel in connection with the preparation of this
Amendment and the
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documents and instruments incidental hereto. The Borrower hereby agrees that the
Lender may, at any time or from time to time in its sole discretion and without
further authorization by the Borrower, make a loan to the Borrower under the
Credit Agreement, or apply the proceeds of any loan, for the purpose of paying
any such fees, disbursements, costs and expenses and the accommodation fee
pursuant to Paragraph 4 hereof.

     12.  Miscellaneous.  This Amendment and the Acknowledgment and Agreement of
          -------------
Guarantors may be executed in any number of counterparts, each of which when so
executed and delivered shall be deemed an original and all of which
counterparts, taken together, shall constitute one and the same instrument.

     IN WITNESS WHEREOF, the parties hereto have caused this Fourth Amendment to
Credit and Security Agreement and Amendment of Default Letter to be duly
executed as of the date first written above.

WELLS FARGO BUSINESS CREDIT, INC.         P. G. DESIGN ELECTRONICS, INC.



By:  /s/ Thomas Zak                       By:   /s/ Edwin Jacobson
     ----------------------                     ---------------------------
Its: V.P.                                 Its:  Chairman
     ----------------------                     ---------------------------

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                   ACKNOWLEDGMENT AND AGREEMENT OF GUARANTORS


     The undersigned, each a guarantor of the indebtedness of P. G. Design
Electronics, Inc. (the "Borrower") to Wells Fargo Business Credit, Inc.,
formerly known as Norwest Business Credit, Inc. (the "Lender"), pursuant to a
separate Guaranty each dated as of December 31, 1998 (each, a "Guaranty"),
hereby (i) acknowledges receipt of the foregoing Amendment; (ii) consents to the
terms (including, without limitation, the release set forth in Paragraph 10 of
the Amendment) and execution thereof; (iii) reaffirms its obligations to the
Lender pursuant to the terms of its Guaranty; and (iv) acknowledges that the
Lender may amend, restate, extend, renew or otherwise modify the Credit
Agreement and any indebtedness or agreement of the Borrower, or enter into any
agreement or extend additional or other credit accommodations, without notifying
or obtaining the consent of the undersigned and without impairing the liability
of the undersigned under its Guaranty for all of the Borrower's present and
future indebtedness to the Lender.

                                   HEARTLAND TECHNOLOGY, INC.


                                   By:  /s/ Edwin Jacobson
                                        --------------------------
                                   Its: Chairman
                                        --------------------------

                                   ZECAL CORP.


                                   By:  /s/ Edwin Jacobson
                                        ---------------------------
                                   Its: Chairman
                                        ---------------------------

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