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                                                                   EXHIBIT 10.31

                 THIRD AMENDMENT TO NOTE AND SECURITY AGREEMENT
                 ----------------------------------------------

          THIS THIRD AMENDMENT TO NOTE AND SECURITY AGREEMENT (this "Agreement")
made as of this 28th day of May, 1997 between RF POWER PRODUCTS, INC., a New
Jersey corporation (the "Borrower"), and MELLON BANK, N.A., a national banking
association (the "Bank").


                             W I T N E S S E T H :


          WHEREAS, the Borrower is the maker of a certain Note and Security
Agreement to the Bank in the original principal amount of Four Million Dollars
($4,000,000.00) dated May 24, 1996 (the "Note") (capitalized terms used herein
but not defined in this Agreement shall have the meaning ascribed to them in the
Note);

          WHEREAS, the Note was previously amended in order to permit, among
other things, equipment financing in the amount of $500,000  pursuant to that
certain First Amendment to Note and Security Agreement dated as of January 17,
1997;

          WHEREAS, the Note was also amended in order to allow the Borrower to
term out and reduce the principal amount outstanding under the Note by $500,000
(to $3,500,000) pursuant to that certain Second Amendment to Note and Security
Agreement dated as of February 27, 1997;

          WHEREAS, the Borrower has requested that the Bank further amend
certain provisions of the Note in order to elect the term-out of an additional
$500,000; and

          WHEREAS, the Bank is willing to grant such request, subject to the
terms and conditions of this Agreement.

          NOW, THEREFORE, in consideration of the mutual promises contained
herein and in the Credit Amendment referred to below, and intending to be
legally bound, the Borrower and the Bank hereby covenant and agree as follows:

          1.  Amendments.  Upon the satisfaction of any condition precedent
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contained in the Third Amendment to Revolving Line of Credit Agreement dated as
of even date herewith (the "Credit Amendment") and the execution and delivery of
this Agreement by the Borrower and the Bank, the Note shall be amended as
follows:

          (a)  The Note shall be amended to reflect that notwithstanding any
provision in the Note to the contrary, the maximum principal amount of the Note
has been reduced to $3,000,000 by virtue of the Borrower's election of the term-
out option set forth in Section 3 of the Supplement to Note and Security
Agreement (the "Supplement") annexed to and made a part of the Note.  Wherever
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the figure $3,500,000 shall appear in the Note or the Supplement, it shall be
replaced with the figure $3,000,000.

          (b)  The Note shall be amended to reflect that references in the Note
to the "Credit Agreement" shall be references to the Revolving Line of Credit
Agreement as amended by the Credit Amendment and as may be still further
amended, modified or supplemented from time to time.

          2.  Election of Alternative Principal Amortization.  The Borrower
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hereby elects the term-out option set forth in Section 3 of the Supplement such
that $500,000 of the outstanding principal balance of the Note as of this date
shall be amortized over a FORTY-EIGHT (48) MONTH PERIOD.  This amount is in
addition to the $500,000 amount previously chosen by the Borrower to be
amortized which is currently evidenced by a Note and Security Agreement dated
February 27, 1997 from the Borrower in favor of the Bank (the "New Note").
Simultaneous with the execution and delivery of this Agreement, the New Note
shall be amended in order to reflect the increase in the face amount of the New
Note from $500,000 to $1,000,000.

          3.  Representations and Warranties.  The Borrower hereby represents
              ------------------------------                                 
and warrants to the Bank that the Borrower is not in default under the Note, the
Credit Agreement or any other document executed in connection therewith.

          4.  Other Terms Confirmed.  All other terms and conditions of the
              ---------------------                                        
Note, including, without limitation, the supplements annexed thereto and made a
part thereof, are hereby confirmed and shall remain in full force and effect
without modification.  From and after the effectiveness of the amendments set
forth in Section 1 hereof, all references in any document or instrument to the
Note shall mean the Note as amended by this Agreement.

          5.  No New Indebtedness.  The Borrower specifically acknowledges and
              -------------------                                             
agrees that neither this Agreement nor the New Note shall represent in any way
the extension of any new credit by the Bank to the Borrower, or the satisfaction
of any indebtedness evidenced by the Credit Agreement or the Note as amended
hereby.

          6.  Counterparts.  This Agreement may be executed in any number of
              ------------                                                  
counterparts, each of which shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument.

          7.  Headings.  The descriptive headings which are used in this
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Agreement are for convenience only and shall not affect the meaning of any
provision of this Agreement.

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          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed by their duly authorized officers as of the day and year first
written above.

Attest:                             RF POWER PRODUCTS, INC.



  /s/ Paul S. Zaun                       /s/ Domenic N. Golato
--------------------                -----------------------------
Name:                               By:  Domenic N. Golato
Title:                                   Chief Financial Officer

[Corporate Seal]

                                    MELLON BANK, N.A.



                                    By:   /s/ Anthony W. LaMarca
                                       -------------------------
                                       Anthony W. LaMarca
                                       Vice President

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