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                                                                 Exhibit 10.5(a)


                       AMENDMENT TO EMPLOYMENT AGREEMENT
                       ---------------------------------

     This Amendment made as of the 5th day of November, 1999, to an Employment
Agreement made as of the 8th day of January, 1998 between EG&G, Inc., now
PerkinElmer, Inc., a Massachusetts corporation (hereinafter called the
"Company"), and Gregory L. Summe (hereinafter referred to as the "Employee").

                                  WITNESSETH:
                                  -----------

     WHEREAS, the Employee and the Company entered into an Employment Agreement
dated as of the 8th day of January, 1998; and

     WHEREAS, the Employee and the Company wish to amend said Employment
Agreement; and

     NOW, THEREFORE, in consideration of the mutual covenants herein contained,
the parties agree as follows, effective as of the date hereof:

     1.   Paragraph 6(a)(iv) of the Employment Agreement is hereby amended to
          read in its entirety as follows:

              Paragraph 5g shall be amended to read in its entirety as follows:

              "Notwithstanding the foregoing provisions, if, within 36 months
              following the occurrence of a Change in Control, the Employee's
              employment by the Company is terminated (A) by the Company other
              than for Cause, which shall not include any failure to perform his
              duties hereunder after giving notice or termination for Good
              Reason, disability or death or (B) by the Employee for Good
              Reason, (1) the Company shall pay to the Employee, on the date of
              his employment termination, a lump sum cash payment in an amount
              equal to the sum of (x) his unpaid base salary through the date of
              termination, (y) pro rata portion of prior year's bonus and (z)
              his Full Salary (as defined below) multiplied by three and (2) the
              Employee shall for 36 months



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                       Amendment to Employment Agreement


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          following the occurrence of the Change in Control be eligible to
          participate in all employee benefit plans and arrangements of the
          Company (such as life, health and disability insurance and automobile
          arrangements but excluding incentive arrangements and grants of stock
          options) to the same extent (including coverage of dependents, if any)
          and upon the same terms as were in effect immediately prior to his
          termination. For purposes of this Agreement, "Full Salary" shall mean
          the Employee's annual base salary, plus the amount of any bonus or
          incentive payments received by the Employee with respect to the last
          full fiscal year of the Company for which all bonus or incentive
          payments to be made have been made. Payments under this Paragraph 5f
          shall be made without regard to whether the deductibility of such
          payments (or any other "parachute payments," as that term is defined
          in Section 280G of the Internal Revenue Code of 1986, as amended (the
          "Code"), to or for the benefit of the Employee) would be limited or
          precluded by Section 280G and without regard to whether such payments
          (or any other "parachute payments" as so defined in said Section 280G)
          would subject the Employee to the federal excise tax levied on
          certain "excess parachute payments" under Section 4999 of the Code
          (the "Excise Tax"). In addition, the Employee shall be entitled to
          receive a payment (the "Gross-Up Payment") which shall be an amount
          equal to the sum of (a) the Excise Tax imposed on any parachute
          payment, whether or not payable under this Agreement, and (b) the
          amount necessary to pay all additional taxes imposed on (or
          economically borne by) the Employee (including the Excise Tax, state
          and federal income taxes and all applicable withholding taxes)
          attributable to the receipt of the Gross-Up Payment, computed assuming
          the application of the maximum tax rates provided by law, so that
          after the payment of all applicable income taxes and excise taxes, the
          Employee will be in the same economic position in which he would have
          been if the Excise Tax had not been applicable. The determination of
          the Gross-Up Payment shall be made


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                       Amendment to Employment Agreement


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              at the Company's expense by Arthur Andersen & Co. or by such other
              certified public accounting firm as the Board of Directors of the
              Company may designate prior to a Change in Control of the Company.
              In the event of any underpayment or overpayment under this
              Paragraph 5g as determined by Arthur Andersen & Co. (or such other
              firm as may have been designated in accordance with the preceding
              sentence), the amount of such underpayment or overpayment shall
              forthwith be paid to the Employee or refunded to the Company, as
              the case may be, with interest at the applicable federal rate
              provided for in Section 7872(f)(2) of the Code."

     2.   Except as provided above, the Employment Contract shall continue in
          full force and effect.

     IN WITNESS WHEREOF, the Company has caused its seal to be hereunto affixed
and these presents to be signed by its proper officers, and the Employee has
hereunto set his hand and seal the day and year first above written.

(SEAL)                             PerkinElmer, Inc.


                                   By: /s/ Terrance L. Carlson
                                       ----------------------------------------
                                   Terrance L. Carlson
                                   SVP, Business Development & General
                                   Counsel


                                   Employee: /s/ Gregory L. Summe
                                       ----------------------------------------




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                       Amendment to Employment Agreement


<PAGE>   4


                              EMPLOYMENT AGREEMENT
                              --------------------

     This Agreement made as of the 8th day of January, 1998, between EG&G, Inc.,
     a Massachusetts corporation (hereinafter called the "Company"), and Gregory
     L. Summe of Phoenix, Arizona (hereinafter referred to as the "Employee").

                                  WITNESSETH:
                                  -----------
     WHEREAS, the Employee will be employed in a management position with the
     Company; and

     WHEREAS, the Employee hereby agrees to continue to perform such services
     and duties of a management nature as shall be assigned to him; and

     NOW, THEREFORE, in consideration of the sum of One Dollar, and of the
     mutual covenants herein contained, the parties agree as follows:

1.   a)   Except as hereinafter otherwise provided, the Company agrees to employ
          the Employee in a management position with the Company, and the
          Employee agrees to remain in the employment of the Company in that
          capacity for a period of three years from the date hereof and for
          three year terms thereafter until such time as this Agreement is
          terminated.

     b)   The Company will, during each year of the term of this Agreement,
          place in nomination before the Board of Directors of the Company the
          name of the Employee for election as an Officer of the Company except
          when a notice of termination has been given in accordance with
          Paragraph 5(b).

2.   The Employee agrees that, during the specified period of employment, he
     shall, to the best of his ability, perform his duties, and shall not engage
     in any business, profession or occupation which would conflict with the
     rendition of the agreed upon services, either directly or indirectly,
     without the prior approval of the Board of Directors.

3.   During the period of his employment under this Agreement, the Employee
     shall be compensated for his services as follows:

     a)   Except as otherwise provided in this Agreement, he shall be paid a
          salary during the period of this Agreement at a base rate to be
          determined by the Company on an annual basis. Except as Provided in
          Subparagraph 3d, such annual base salary shall under no circumstances
          be fixed at a rate below the annual base rate then currently in
          effect;

     b)   He shall be reimbursed for any and all monies expended by him in
          connection with his employment for reasonable and necessary expenses
          on behalf of the Company in accordance with the policies of the
          Company then in effect;

     c)   He shall be eligible to participate under any and all bonus, benefit,
          pension, compensation, and option plans which are, in accordance with
          company policy, available to persons in his position (within the
          limitation as stipulated by such plans). Such eligibility shall not
          automatically entitle him to participate in any such plan;

     d)   If, because of adverse business conditions or for other reasons, the
          Company at any time puts into effect salary reductions applicable to
          all management employees of the Company generally, the salary payments
          required to be made under this Agreement to the Employee during any
          period in which such general reduction is in effect may be reduced by
          the same percentage as is applicable to all management employees of
          the Company generally. Any benefits made available



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<PAGE>   5


          to the Employee which are related to base salary shall also be reduced
          in accordance with any salary reduction.

4.   a)   During the period of his employment by the Company or for any period
          which the Company shall continue to pay the Employee his salary under
          this Agreement, whichever shall be the longer, the Employee shall not
          directly or indirectly own, manage, control, operate, be employed by,
          participate in or be connected with the ownership, management,
          operation or control of any business which competes with the Company
          or its subsidiaries, provided, however, that the foregoing shall not
          apply to ownership of stock in a publicly held corporation which
          ownership is disclosed to the Board of Directors nor shall it apply to
          any other relationship which is disclosed to and approved by the Board
          of Directors.

     b)   During the period of his employment by the Company and two years
          following the Company's last payment of salary to him, the Employee
          shall not utilize or disclose to others any proprietary or
          confidential information of any type or description which term shall
          be construed to mean any information developed or identified by the
          Company which is intended to give it an advantage over its competitors
          or which could give a competitor an advantage if obtained by it. Such
          information includes, but is not limited to, product or process
          design, specifications, manufacturing methods, financial or
          statistical information about the Company, marketing or sales
          information about the Company, sources of supply, lists of customers,
          and the Company's plans, strategies, and contemplated actions.

     c)   During the period of his employment by the Company or for any period
          during which the Company shall continue to pay the Employee his salary
          under this Agreement, whichever shall be longer, the Employee shall
          not in any way whatsoever aid or assist any party seeking to cause,
          initiate or effect a Change in Control of the Company as defined in
          Paragraph 6 without the prior approval of the Board of Directors.

5.   Except for the Employee covenants set forth in Paragraph 4 which covenants
     shall remain in effect for the periods stated therein, and subject to
     Paragraph 6, this Agreement shall terminate upon the happening of any of
     the following events and (except as provided herein) all of the Company's
     obligations under this Agreement, including, but not limited to, making
     payments to the Employee shall cease and terminate:

     a)   On the effective date set forth in any resignation submitted by the
          Employee and accepted by the Company, or if no effective date is
          agreed upon, the date of receipt of such letter;

     b)   Three years after written notice of termination is given by either
          party to the other party;

     c)   At the end of the month in which the Employee shall have attained the
          age of sixty-five years;

     d)   At the death of the Employee;

     e)   At the termination of the Employee for cause. As used in the
          Agreement, the term "cause" shall mean:

          i)   Misappropriating any funds or property of the Company;

          ii)  Unreasonable refusal to perform the duties assigned to him under
               this Agreement;

          iii) Conviction of a felony;

          iv)  Violation of the Employee's covenants as set forth in Paragraph 4
               above; or


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          v)   Continued failure by the Employee to observe any of the
               provisions of this Agreement after being informed of such breach.

     f)   At termination of the Employee by the Company without cause.

     g)   Twelve months after written notice of termination is given by the
          Company to the Employee based on a determination by the Board of
          Directors that the Employee is disabled (which, for purposes of this
          Agreement, shall mean that the Employee is unable to perform his
          regular duties, with such determination to be made by the Board of
          Directors, in reliance upon the opinion of the Employee's physician or
          upon the opinion of one or more physicians selected by the Company).
          Such notice shall be given by the Company to the Employee on the 184th
          day of continuous disability of the Employee. Notwithstanding the
          foregoing, if, during the twelve-month notice period referred to
          above, the Employee is no longer disabled and is able to return to
          work, such notice of employment termination shall be rescinded, and
          the employment of the Employee shall continue in accordance with the
          terms of this Agreement. During the first 184 days of continuous
          disability of the Employee, the Company will make periodic payments to
          the Employee in an amount equal to the difference between his base
          salary and the benefits provided by the Company's Short-Term
          Disability Income Plan. During the twelve-month notice period
          following 184 days of continuous disability, the Company will make
          periodic payments to the Employee in an amount equal to the difference
          between his base salary and the benefits provided by the Company's
          Long-Term Disability Plan. If the employment of the Employee
          terminates at the end of such twelve-month notice period, the Company
          will make periodic payments to the Employee in an amount equal to the
          difference between his base pay and the post-employment benefits
          provided to him under the Company's Long-Term Disability Plan. Due to
          the fact that payments to the Employee under the Company's Long-Term
          Disability Plan are not subject to federal income taxes, the payments
          to be made directly by the Company pursuant to the two preceding
          sentences shall be reduced such that the total amount received by the
          Employee (from the Company and from the Long-Term Disability Plan),
          after payment of any income taxes, is equal to the amount that the
          Employee would have received had he been paid his base salary, after
          payment of any income taxes on such base salary.

     h)   Notwithstanding the foregoing provisions, in the event of the
          termination of the Employee by the Company without cause, the Employee
          shall, until the expiration of his then current employment term or
          three years from the date of such termination, whichever is later, (i)
          continue to receive his Full Salary (as defined below), which shall be
          payable in accordance with the payment schedule in effect immediately
          prior to his employment termination, and (ii) continue to be entitled
          to participate in all employee benefit plans and arrangements of the
          Company (such as life, health and disability insurance and automobile
          arrangements) to the same extent (including coverage of dependents, if
          any) and upon the same terms as were in effect immediately prior to
          his termination. For purposes of this Agreement, "Full Salary" shall
          mean the Employee's annual base salary, plus the amount of any bonus
          or incentive payments received by the Employee with respect to the
          last full fiscal year of the Company for which all bonus or incentive
          payments to be made have been made.

6.   a)   In the event that there is a Change in Control of the Company (as
          defined below), the provisions of this Agreement shall be amended as
          follows:

          i)   Paragraph 1a shall be amended to read in its entirety as follows:

               "Except as hereinafter otherwise provided, the Company agrees to
               continue to employ the Employee in a management position with the
               Company, and the Employee agrees to remain in the employment in
               the Company in that capacity, for a period of five (5) years less
               one day from the date of the Change in Control. Except as
               provided in Paragraph 3d, the Employee's salary as set forth in
               Paragraph 3a and his other employee benefits, pursuant to the
               plans described in Paragraph 3c shall not be decreased during
               such period."


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          ii)  Paragraph 5a shall be amended by the addition of the following
               provision at the end of such paragraph:

               ", provided that the Employee agrees not to resign, except for
               Good Reason (as defined below), during the one-year period
               following the date of the Change in Control."

          iii) Paragraph 5b shall be deleted in its entirety.

          iv)  Paragraph 5h shall be amended to read in its entirety as follows:

               "Notwithstanding the foregoing provisions, in the event of the
               termination of the Employee by the Company without cause, or the
               resignation of the Employee for Good Reason, the Employee shall
               (i) receive, on the date of his employment termination, a cash
               payment in an amount equal to his Full Salary (as defined below)
               multiplied by the number of years (including any portions
               thereof) remaining until the expiration of his then current
               employment term or five years from the date of such termination,
               whichever is later (it being agreed that such amount shall not be
               discounted based upon the present value of such amount), and (ii)
               continue to be entitled to participate in all employee benefit
               plans and arrangements of the Company (such as life, health and
               disability insurance and automobile arrangements) to the same
               extent (including coverage of dependents, if any) and upon the
               same terms as were in effect immediately prior to his
               termination. For purposes of this Agreement, "Full Salary" shall
               mean the Employee's annual base salary, plus the amount of any
               bonus or incentive payments received by the Employee with respect
               to the last full fiscal year of the Company for which all bonus
               or incentive payments to be made have been made. Payments under
               this Paragraph 5h shall be made without regard to whether the
               deductibility of such payments (or any other "parachute
               payments," as that term is defined in Section 280G of the
               Internal Revenue Code of 1986, as amended (the "Code"), to or for
               the benefit of the Employee) would be limited or precluded by
               Section 280G and without regard to whether such payments (or any
               other "parachute payments" as so defined) would subject the
               Employee to the federal excise tax levied on certain "excess
               parachute payments" under Section 4999 of the Code; provided that
               if the total of all "parachute payments" to or for the benefit of
               the Employee, after reduction for all federal, state and local
               taxes (including the tax described in Section 4999 of the Code,
               if applicable) with respect to such payments (the "Total
               After-Tax Payments"), would be increased by the limitation or
               elimination of any payment under this Paragraph 5h, amounts
               payable under this Paragraph 5h shall be reduced to the extent,
               and only to the extent, necessary to maximize the Total After-Tax
               Payments. The determination as to whether and to what extent
               payments under this Paragraph 5h are required to be reduced in
               accordance with the preceding sentence shall be made at the
               Company's expense by Arthur Andersen & Co. or by such other
               certified public accounting firm as the Board of Directors of the
               Company may designate prior to a Change in Control of the
               Company. In the event of any underpayment or overpayment under
               this Paragraph 5h as determined by Arthur Andersen & Co. (or such
               other firm as may have been designated in accordance with the
               preceding sentence), the amount of such underpayment or
               overpayment shall forthwith be paid to the Employee or refunded
               to the Company, as the case may be, with interest at the
               applicable federal rate provided for in Section 7872(f)(2) of the
               Code."

          v)   Paragraph 8 shall be amended to read in its entirety as follows:

               The Employee may pursue any lawful remedy he deems necessary or
               appropriate for enforcing his rights under this Agreement
               following a Change in Control of the Company, and all costs
               incurred by the Employee in connection therewith (including
               without limitation attorneys' fees) shall be promptly reimbursed
               to him by the


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<PAGE>   8


               Company, regardless of the outcome of such endeavor.

     b)   For purposes of this Agreement, a "Change in Control of the Company"
          shall occur or be deemed to have occurred only if (i) any "person", as
          such term is used in Section 13(d) and 14(d) of the Securities
          Exchange Act of 1934, as amended (the "Exchange Act") (other than the
          Company, any trustee or other fiduciary holding securities under an
          employee benefit plan of the Company, or any corporation owned
          directly or indirectly by the stockholders of the Company in
          substantially the same proportion as their ownership of stock in the
          Company), is or becomes the "beneficial owner" (as defined in Rule
          13d-3 under the Exchange Act), directly or indirectly, of securities
          of the Company representing 30% or more of the combined voting power
          of the Company's then outstanding securities; (i) during any period
          of two consecutive years ending during the term of this Agreement,
          individuals who at the beginning of such period constitute the Board
          of Directors of the Company, and any new director whose election by
          the Board of Directors or nomination for election by the Company's
          stockholders was approved by a vote of at least two-thirds of the
          directors then still in office who were either directors at the
          beginning of the period or whose election or whose nomination for
          election was previously so approved, cease for any reason to
          constitute a majority of the Board of Directors; (iii) the
          stockholders of the Company approve a merger or consolidation of the
          Company with any other corporation, other than a merger or
          consolidation which would result in the voting securities of the
          Company outstanding immediately prior thereto continuing to represent
          (either by remaining outstanding or by being converted into voting
          securities of the surviving entity) more than 50% of the combined
          voting power of the voting securities of the Company or such surviving
          entity outstanding immediately after such merger or consolidation; or
          (iv) the stockholders of the Company approve a plan of complete
          liquidation of the Company or an agreement for the sale or disposition
          by the Company of all or substantially all of the Company's assets.

     c)   For purposes of this Agreement, "Good Reason" shall mean the
          occurrence of any of the following events, except as provided in
          Paragraph 3d; (i) a reduction in the Employee's base salary as in
          effect on the date hereof or as the same may be increased from time to
          time; (ii) a failure by the Company to pay annual cash bonuses to the
          Employees in an amount at least equal to the most recent annual cash
          bonuses paid to the Employee; (iii) a failure by the Company to
          maintain in effect any material compensation or benefit plan in which
          the Employee participated immediately prior to the Change in Control,
          unless an equitable arrangement has been made with respect to such
          plan, or a failure to continue the Employee's participation therein on
          a basis not materially less favorable than existed immediately prior
          to the Change in Control; (iv) any significant and substantial
          diminution in the Employee's position, duties, responsibilities or
          title as in effect immediately prior to the Change in Control; (v) any
          requirement by the Company that the location at which the Employee
          performs his principal duties be changed to a new location outside a
          radius of 25 miles from the Employee's principal place of employment
          immediately prior to the Change in Control; or (vi) any requirement by
          the Company that the Employee travel on an overnight basis to an
          extent not substantially consistent with the Employee's business
          travel obligations immediately prior to the Change in Control.
          Notwithstanding the foregoing, the resignation shall not be considered
          to be for Good Reason if any such circumstances are fully corrected
          prior to the date of resignation.

7.   Neither the Employee nor, in the event of his death, his legal
     representative, beneficiary or estate, shall have the power to transfer,
     assign, mortgage or otherwise encumber in advance any of the payments
     provided for in this Agreement, nor shall any payments nor assets or funds
     of the Company be subject to seizure for the payment of any debts,
     judgments, liabilities, bankruptcy or other actions.

8.   Any controversy relating to this Agreement and not resolved by the Board of
     Directors and the Employee shall be settled by arbitration in the City of
     Boston, Commonwealth of Massachusetts, pursuant to the rules then obtaining
     of the American Arbitration Association, and judgment upon the award may be
     entered in any court having jurisdiction, and the Board of Directors and
     Employee agree to be bound by the arbitration decision on any such
     controversy. Unless otherwise agreed by the parties hereto, arbitration
     will be by


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<PAGE>   9


     three arbitrators selected from the panel of the American Arbitration
     Association. The full cost of any such arbitration shall be borne by the
     Company.

9.   Failure to insist upon strict compliance with any of the terms, covenants,
     or conditions hereof shall not be deemed a waiver of such term, covenant,
     or condition, nor shall any waiver or relinquishment of any right or power
     hereunder at any one or more times be deemed a waiver or relinquishment of
     such right or power at any other time or times by either party.

10.  All notices or other communications hereunder shall be in writing and shall
     be deemed to have been duly given when delivered personally to the Employee
     or to the General Counsel of the Company or when mailed by registered or
     certified mail to the other party (if to the Company, at 45 William Street,
     Wellesley, Massachusetts 02481, attention General Counsel; if to the
     Employee, at the last known address of the Employee as set forth in the
     records of the Company).

11.  This Agreement has been executed and delivered and shall be construed in
     accordance with the laws of the Commonwealth of Massachusetts. This
     Agreement is and shall be binding on the respective legal representatives
     or successors of the parties, but shall not be assignable except to a
     successor to the Company by virtue of a merger, consolidation or
     acquisition of all or substantially all of the assets of the Company. All
     previous employment contracts between the Employee and the Company or any
     of the Company's present or former subsidiaries or affiliates is hereby
     canceled and of no effect.

     IN WITNESS WHEREOF, the Company has caused its seal to be hereunto affixed
and these presents to be signed by its proper officers, and the Employee has
hereunto set his hand and seal the day and year first above written.

(SEAL)                          EG&G, INC.


                                By: /s/ Murray Gross
                                    -----------------------------------------
                                    Murray Gross
                                    Senior Vice President & General Counsel


                                Employee: /s/ Gregory L. Summe
                                          -----------------------------------



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