<PAGE>

                                                                   EXHIBIT 10.85

                                 TENTH AMENDMENT
                          DATED AS OF DECEMBER 27, 2002
                                       TO
                           RECEIVABLES SALE AGREEMENT
                           DATED AS OF OCTOBER 1, 1999

      THIS AMENDMENT (the "Amendment"), dated as of December 27, 2002, is
entered into among Ametek Receivables Corp. (the "Seller"), Ametek, Inc. (the
"Initial Collection Agent"), Amsterdam Funding Corporation, a Delaware
corporation ("Amsterdam"), ABN AMRO Bank N.V., as Amsterdam's program letter of
credit provider (the "Enhancer"), the Liquidity Provider listed on the signature
page hereof (the "Liquidity Provider") and ABN AMRO Bank N.V., as agent for
Amsterdam, the Enhancer and the Liquidity Provider (the "Agent").

                                   WITNESSETH:

      WHEREAS, the Seller, Initial Collection Agent, Amsterdam, Enhancer,
Liquidity Provider and Agent have heretofore executed and delivered a
Receivables Sale Agreement, dated as of October 1, 1999 (as amended,
supplemented or otherwise modified through the date hereof, the "Sale
Agreement"),

      WHEREAS, the parties hereto desire to amend the Sale Agreement as provided
herein;

      NOW, THEREFORE, for good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, the parties hereto hereby agree that
the Sale Agreement shall be and is hereby amended as follows:

      Section 1. Subject to the following terms and conditions, including
without limitation the conditions precedent set forth in Section 2, upon
execution by the parties hereto in the space provided for that purpose below,
the Sale Agreement shall be, and it hereby is, amended as follows:

      (a)   The date "December 27, 2002" appearing in clause (d) of the defined
            term "Liquidity Termination" appearing in Schedule I of the Sale
            Agreement is deleted and replaced with the date "November 28, 2003."

      (b)   The date "December 27, 2002" appearing in clause (c)(ii) of the
            defined term "Termination Date" appearing in Schedule I of the Sale
            Agreement is deleted and replaced with the date "November 28, 2003."

      (c)   The defined term "Eligible Receivables" appearing in Schedule I of
            the Sale Agreement is hereby amended by deleting clause (x) thereof.

      (d)   The following sentence shall be added at the end of Section 9.11 of
            the Sale Agreement:
<PAGE>
      "The provisions of this Section 9.11 shall survive termination of this
Agreement."

      (e)   The following sentence shall be added at the end of Section 9.12:

      "The provisions of this Section 9.12 shall survive termination of this
Agreement."

      (f)   Exhibit F to the Sale Agreement is hereby amended in its entirety to
            be read as Exhibit F attached hereto.

      Section 2. Section 1 of this Amendment shall become effective only once
the Agent has received in, form and substance satisfactory to the Agent (i) all
documents and certificates as the Agent may reasonably request and (ii) all
other matters incident to the execution thereof.

      Section 3. To induce the Agent and the Purchasers to enter into this
Amendment, the Seller and Initial Collection Agent represent and warrant to the
Agent and the Purchasers that: (a) the representations and warranties contained
in the Transaction Documents, are true and correct in all material respects as
of the date hereof with the same effect as though made on the date hereof (it
being understood and agreed that any representation or warranty which by its
terms is made as of a specified date shall be required to be true and correct in
all material respects only as of such specified date); (b) no Potential
Termination Event exists; (c) this Amendment has been duly authorized by all
necessary corporate proceedings and duly executed and delivered by each of the
Seller and the Initial Collection Agent, and the Sale Agreement, as amended by
this Amendment, and each of the other Transaction Documents are the legal, valid
and binding obligations of the Seller and the Initial Collection Agent,
enforceable against the Seller and the Initial Collection Agent in accordance
with their respective terms, except as enforceability may be limited by
bankruptcy, insolvency or other similar laws of general application affecting
the enforcement of creditors' rights or by general principles of equity; and (d)
no consent, approval, authorization, order, registration or qualification with
any governmental authority is required for, and in the absence of which would
adversely effect, the legal and valid execution and delivery or performance by
the Seller or the Initial Collection Agent of this Amendment or the performance
by the Seller or the Initial Collection Agent of the Sale Agreement, as amended
by this Amendment, or any other Transaction Document to which they are a party.

      Section 3.1. This Amendment may be executed in any number of counterparts
and by the different parties on separate counterparts and each such counterpart
shall be deemed to be an original, but all such counterparts shall together
constitute but one and the same Amendment.

      Section 3.2. Except as specifically provided above, the Sale Agreement and
the other Transaction Documents shall remain in full force and effect and are
hereby ratified and confirmed in all respects. The execution, delivery, and
effectiveness of this Amendment shall not operate as a waiver of any right,
power, or remedy of any Agent or any Purchaser under the Sale Agreement or any
of the other Transaction Documents, nor constitute a waiver or modification of
any provision of any of the other Transaction Documents. All defined terms



                                      -2-
<PAGE>
used herein and not defined herein shall have the same meaning herein as in the
Sale Agreement. The Seller agrees to pay on demand all costs and expenses
(including reasonable fees and expenses of counsel) of or incurred by the Agent
and each Purchaser Agent in connection with the negotiation, preparation,
execution and delivery of this Amendment.

      Section 3.3. This Amendment and the rights and obligations of the parties
hereunder shall be construed in accordance with and be governed by the law of
the State of New York.




                                      -3-
<PAGE>
      IN WITNESS WHEREOF, the parties have caused this Amendment to be executed
and delivered by their duly authorized officers as of the date first above
written.

                            ABN AMRO BANK N.V., as the Agent, as the Liquidity
                            Provider and as the Enhancer


                            By: Patricia Luken
                                --------------------------
                               Title: Group Vice President

                            By: Nancy C. Beebe
                                --------------------------
                               Title: Group Vice President

                            AMSTERDAM FUNDING CORPORATION

                            By: Andrew L. Stidd
                                --------------------------
                               Title: President

                            AMETEK RECEIVABLES CORP.

                            By: Deirdre D. Saunders
                                --------------------------
                               Title: Treasurer

                            AMETEK, INC.

                            By: Deirdre D. Saunders
                                --------------------------
                               Title: Vice President & Treasurer



                                      -4-
<PAGE>
                                    EXHIBIT F

                          LOCK BOXES AND WIRE ACCOUNTS
<TABLE>
<CAPTION>
   BANK                                 LOCK BOX #                     DIVISION
<S>                                     <C>                       <C>
First Union                                6035                   Aerospace Products
First Union                              601461                   Lamb Electric
First Union                              601471                   Rotron, Inc.
First Union                                7455                   Specialty Metals-84, PA
First Union                                7915                   Specialty Metals-CT
First Union                              601456                   TMD Division
First Union                                8275                   U.S. Gauge Division
Comerica                                  26601                   Prestolite Power and Switch Division
First Union                               18516                   EDAX, Inc.
Bank of America                            2325                   Patriot Sensors and Controls Corp.
Bank of America                            3770
Bank of America                           99031
First Union                              601175                   Advanced Measurement Technology, Inc.
</TABLE>

<TABLE>
<CAPTION>
   BANK                               WIRE ACCOUNT #                   DIVISION
<S>                                 <C>                         <C>
Chase Manhattan                       910-2-791010               Aerospace Products
Chase Manhattan                        323-866-565               Lamb Electric
Chase Manhattan                        323-850-790               Rotron/TMD
Chase Manhattan                        323-866-573               Specialty Metals
Chase Manhattan                       910-2-791051               U.S. Gauge Division
Chase Manhattan                       910-2-791036               Test & Calibration Division
Chase Manhattan                       910-2-791044               Process & Analytical Instruments
First Union                          2030001065067               EDAX, Inc.
</TABLE>