<PAGE>   1

                                                                [Exhibit 10.1.6]

             AMENDMENT NO. 6 TO CREDIT AGREEMENT AND LIMITED WAIVER


         This AMENDMENT NO. 6 TO CREDIT AGREEMENT AND LIMITED WAIVER (this
"Limited Waiver") is made and entered into as of July 26, 1999 among
COMMUNICATIONS & POWER INDUSTRIES, INC. (the "Borrower"), COMMUNICATIONS & POWER
INDUSTRIES HOLDING CORPORATION, CPI SUBSIDIARY HOLDINGS INC., COMMUNICATIONS &
POWER INDUSTRIES INTERNATIONAL INC., COMMUNICATIONS & POWER INDUSTRIES ASIA
INC., COMMUNICATIONS & POWER INDUSTRIES ITALIA S.R.L., COMMUNICATIONS & POWER
INDUSTRIES EUROPE LIMITED, COMMUNICATIONS & POWER INDUSTRIES CANADA INC.,
COMMUNICATIONS & POWER INDUSTRIES AUSTRALIA PTY LIMITED, CPI SALES CORP.
(collectively, the "Obligors"), BANKERS TRUST COMPANY, as agent (the "Agent"),
and the various lenders (the "Lenders") from time to time party to the Credit
Agreement, dated as of August 11, 1995 (as amended by Amendment No. 1, dated as
of December 31, 1996, Amendment No. 2, dated as of April 1, 1997, Amendment No.
3, dated as of June 27, 1997, Amendment No. 4, dated as of October 6, 1998, and
Amendment No. 5, dated as of February 12, 1999, the "Agreement"), among the
Obligors, the Agent and the Lenders.

                                    RECITALS

         A. The Borrower has (1) failed to deliver the amended financial
statements and Borrowing Base Certificate for the April, 1999 Fiscal Month and
the financial statements and Borrowing Base Certificate for the May, 1999 Fiscal
Month, in each case required to be delivered under paragraph 2 of Annex D to the
Agreement at the times required therein (the "Reporting Default") and (2)
informed the Agent and the Lenders that it expects to fail to meet the financial
covenants contained in paragraphs 1, 2 and 3 of Annex F of the Agreement for the
Fiscal Quarter ending June 30, 1999 (the "Financial Covenant Default").

         B. The Borrower has requested that the Lenders waive the Reporting
Default and the Financial Covenant Default (collectively, the "Defaults").

         NOW, THEREFORE, the parties hereto hereby agree as follows:

         1. Defined Terms. Unless otherwise defined herein, capitalized terms
used herein shall have the meanings given thereto in the Agreement.

         2. Effectiveness of this Limited Waiver. This Limited Waiver shall
become effective as of the date hereof ("Effectiveness") upon satisfaction of
each of the following conditions:

            (a) Lenders comprising Requisite Lenders shall have executed a
counterpart to this Limited Waiver and shall have delivered the same to the
Agent; and

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            (b) each Lender shall have received a fee in immediately available
funds equal to the product of (i) 0.125% and (ii) the aggregate amount of such
Lender's Commitments, which fee shall be credited against any upfront fee
payable to such Lender upon the effectiveness of any amendment to the Agreement
in form and substance satisfactory to the Obligors, the Agent and the Lenders
pursuant to which the Defaults shall be permanently waived and the Loans, or any
terms thereof or covenants relating thereto, will be restructured (the
"Restructuring Amendment").

         3. Limited Waiver. Subject to Effectiveness, the Lenders hereby waive
each of the Defaults for a period (the "Waiver Period") beginning on the first
date of Effectiveness and ending on the earliest of (i) July 26, 1999, unless
the Borrower shall have delivered to each Lender on or prior to such date the
financial statements and Borrowing Base Certificate required to be delivered
under paragraph 2 of Annex D to the Agreement for the May, 1999 Fiscal Month,
(ii) the Non-Compliance Date (as defined below), (iii) the date of effectiveness
of the Restructuring Amendment and (iv) October 1, 1999. For purposes hereof,
"Non-Compliance Date" shall mean the earlier of (x) the date on which the
Borrower delivers to the Agent and each Lender the certification of its Chief
Financial Officer for the Borrower's Fiscal Quarter ended June 30, 1999 required
by paragraph 3 of Annex D to the Agreement if such certification shows that for
the Test Period covered thereby the Interest Coverage Ratio is less than
1.25:1.00 or the Leverage Ratio is more than 7.25:1.00 and (y) the date on which
the Borrower defaults in its obligation to deliver to the Agent and each Lender
the certification referred to in clause (x) at the time set forth in paragraph 3
of Annex D to the Agreement.

         4. Additional Agreements. The following provisions shall apply at all
times prior to the effectiveness of the Restructuring Amendment:

            (a) Interest Rates.

                (i)      The "Applicable Base Rate Margin" shall mean a rate per
         annum determined as follows: (A) in the case of the Revolving Credit
         Loan and Term Loan A, 1.25% per annum, (B) in the case of Term Loan B,
         1.75% per annum and (C) in the case of Swingline Loans, 0.75% per
         annum.

                (ii)     The "Applicable Eurodollar Rate Margin" shall mean a
         rate per annum determined as follows: (A) in the case of the Revolving
         Credit Loan and Term Loan A, 2.75% per annum and (B) in the case of
         Term Loan B, 3.25% per annum.

            (b) Eurodollar Loan Interest Periods. The Borrower may not elect any
new Interest Period pursuant to Section 1.8(e)(ii) of the Agreement in respect
of any borrowing of a Eurodollar Loan longer than a three month period.

            (c) Further Restrictions. Without limiting any of the restrictions
otherwise contained in the Agreement, no Obligor shall:

                (i)      directly or indirectly, by operation of law or
         otherwise, enter into a merger, acquisition or joint venture for the
         purposes described in clause (c) of Section 6.1 of the Agreement;

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                (ii)     make any investment in, or make or accrue loans or
         advances of money or extend credit to, any Person, through the direct
         or indirect holding of securities or otherwise, or purchase or acquire
         any stock, obligations or securities of, or make any capital
         contribution to, any Person for the purposes described in clauses (e)
         or (g) of the defined term "Permitted Investments" set forth in Annex A
         to the Agreement;

                (iii)    create, incur, assume or permit to exist any
         Indebtedness described in clauses (i) or (o) of the defined term
         "Permitted Indebtedness" set forth in Annex A to the Agreement other
         than any such Indebtedness existing on or before June 30, 1999;

                (iv)     enter into any transactions described in clauses (c),
         (f) or (j) of the defined term "Permitted Affiliate Transactions" set
         forth in Annex A to the Agreement; or

                (v)      make any investments, incur any Indebtedness or
         otherwise make any payments for the purposes described in clause (b) of
         Section 6.14 of the Agreement (other than the payments described in
         sub-clauses (iii)(B) and (iii)(D) of such clause (b)).

            (d) EBITDA. The Borrower will not permit Consolidated EBITDA for the
immediately preceding twelve Fiscal Months, determined as of the last day of
each month, to be less than $21,000,000.

            (e) Financial Reports. At the time of and together with the delivery
of the internally prepared Consolidated income statement, statement of cash
flows and balance sheet required to be provided by the Borrower under paragraph
2 of Annex D to the Agreement (the "Monthly Financials"), the Borrower will
provide to each Lender (i) copies of its internally prepared financial
statements of each division of the Borrower in a format consistent with the
Monthly Financials, (ii) in lieu of comparisons to the budget for that monthly
period and the year to date period, comparisons for such periods of the Monthly
Financials to the forecasts and projections delivered to the Agent and the
Lenders by the Borrower on July 12, 1999 and (iii) a certification of the Chief
Financial Officer of Borrower that Borrower is or is not, as the case may be, in
compliance with the terms of Section 4(d) of this Limited Waiver and showing in
reasonable detail the calculations used in determining such compliance or
non-compliance.

            (f) Mandatory Prepayment. Notwithstanding anything to the contrary
contained in Section 1.8(e)(i) of the Agreement, if at any time the Borrower's
aggregate cash balances exceed $1,099,999 (excluding non-US cash balances
required in connection with contract advances), the Borrower shall promptly pay,
without premium or penalty, cash in excess of $1,000,000 in minimum amounts of
$100,000 and integral multiples thereof to the Agent for application (i) first,
to outstanding amounts under the Swingline Loan and (ii) second, to outstanding
amounts under the Revolving Credit Loan in accordance with Section 1.4(e) of the
Agreement. For purposes of this clause (f), prepayments hereunder shall be
applied first to outstanding Base Rate Loans and then to outstanding Eurodollar
Loans, provided that Borrower shall at all times remain obligated to pay
breakage costs pursuant to Section 1.9(e)(ii) of the Agreement. So long as
Borrower's aggregate cash balances do not exceed $1,099,999 (excluding non-US
cash balances required in connection with contract advances), payments hereunder
may be reborrowed from time to time subject to the terms and conditions of the
Agreement.


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         5. Miscellaneous.

            (a) The waiver given hereby is made once only with respect to the
specific provisions of the Agreement set forth above and is made only to the
extent and for the limited purpose and period described herein. Such waiver is
not to be construed as a waiver for any purpose other than as specifically set
forth in this Limited Waiver and shall not constitute an agreement or obligation
of the Agent or any Lender to grant any other or any future waiver.

            (b) Upon expiration of the Waiver Period (other than upon the
effectiveness of the Restructuring Amendment), each of the Defaults waived
hereunder shall, unless cured prior to such time, be reinstated in full as of
the date of such expiration. No failure or delay in accordance with this Limited
Waiver on the part of the Agent or any Lender in exercising any right, power or
privilege under the Agreement in respect of the Defaults shall operate as a
waiver of any such right, power or privilege in the event that the Defaults (or
any of them) are reinstated. No waiver of the Defaults hereunder shall suspend,
waive or effect any other Default or Event of Default under the Agreement.

            (c) Except as expressly modified by this Limited Waiver, the
Agreement shall continue to be and remain in full force and effect in accordance
with its terms.

            (d) This Limited Waiver may be executed in any number of
counterparts, each of which shall constitute an original, but all of which when
taken together shall constitute but one instrument.

            (e) THIS LIMITED WAIVER SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

            (f) This Limited Waiver may be executed by facsimile signature and
each such signature shall be treated in all respects as having the same effect
as an original signature.

            (g) Each Obligor hereby ratifies, affirms, acknowledges and agrees
that the Agreement (as modified herein) and each of the other Loan Documents to
which it is a party constitute its valid, binding and enforceable obligations,
and each such Obligor further acknowledges that there are no existing claims,
counterclaims, defenses or rights of setoff whatsoever with respect to the
Agreement (as modified herein) or any of the other Loan Documents.

            (h) Each Obligor fully, finally, and absolutely and forever releases
and discharges the Agent and each Lender and their present and former directors,
shareholders, officers, employees, agents, representatives, successors and
assigns, and their separate and respective heirs, personal representatives,
successors and assigns, from any and all actions, causes of action, claims,
debts, damages, demands, liabilities, obligations, and suits, of whatever kind
or nature, in law or equity of such Obligor, whether now known or unknown to
such Obligor, and whether contingent or matured, (i) in respect of the Loans,
the Loan Documents, or the actions or omissions of the Agent and the Lenders in
respect of the Loans or the Loan Documents and (ii) arising from events
occurring prior to the date of this Limited Waiver.


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            IN WITNESS WHEREOF, the parties hereto have caused this Limited
Waiver to be duly executed as of the date first above written.

                                   COMMUNICATIONS & POWER
                                     INDUSTRIES, INC.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title: Chief Financial Officer, Treasurer
                                              and Secretary


                                   COMMUNICATIONS & POWER
                                   INDUSTRIES HOLDING CORPORATION



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title: Chief Financial Officer, Treasurer
                                              and Secretary


                                   CPI SUBSIDIARY HOLDINGS INC.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title: Secretary


                                      -5-
<PAGE>   6

                                   COMMUNICATIONS & POWER
                                   INDUSTRIES INTERNATIONAL INC.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   Secretary


                                   COMMUNICATIONS & POWER
                                   INDUSTRIES ASIA INC.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   Treasurer


                                   COMMUNICATIONS & POWER
                                   INDUSTRIES ITALIA S.R.L.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   (Per Power of Attorney)


                                   COMMUNICATIONS & POWER
                                   INDUSTRIES EUROPE LIMITED



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   Secretary


                                      -6-
<PAGE>   7

                                   COMMUNICATIONS & POWER
                                   INDUSTRIES CANADA INC.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   Vice President


                                   COMMUNICATIONS & POWER
                                   INDUSTRIES AUSTRALIA
                                   PTY LIMITED



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   (Per Power of Attorney)


                                   CPI SALES CORP.



                                   By    /s/LYNN E. HARVEY
                                     -------------------------------------------
                                       Name: Lynn E. Harvey
                                       Title:   Secretary and Treasurer


                                   BANKERS TRUST COMPANY,
                                   as Lender and as Agent



                                   By    /s/MARY JO JOLLY
                                     -------------------------------------------
                                       Name:  Mary Jo Jolly
                                       Title:   Assistant Vice President


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                                   DRESDNER BANK AG,
                                   New York and Grand Cayman Branches



                                   By    /s/BEVERLY G. CASON
                                     -------------------------------------------
                                       Name:  Beverly G. Cason
                                       Title:    Vice President



                                   By    /s/JOHN R. MORRISON
                                     -------------------------------------------
                                       Name:  John R. Morrison
                                       Title:    Vice President


                                   U.S. BANK NATIONAL ASSOCIATION
                                   (f/k/a FIRST BANK NATIONAL ASSOCIATION)



                                   By    /s/KURT D. EGERTSON
                                     -------------------------------------------
                                       Name:  Kurt D. Egertson
                                       Title:    Vice President


                                   MERRILL LYNCH SENIOR FLOATING
                                   RATE FUND, INC.



                                   By    /s/JOSEPH MORONEY
                                     -------------------------------------------
                                       Name:  Joseph Moroney
                                       Title:    Authorized Signatory


                                   ROYALTON COMPANY


                                   By PACIFIC INVESTMENT MANAGEMENT
                                         COMPANY, as Investment Adviser
                                   By PIMCO Management Inc., a general partner


                                   By    /s/MOHAN V. PHASALKAR
                                     -------------------------------------------
                                       Name:   Mohan V. Phansalkar
                                       Title:     Senior Vice President


                                      -8-
<PAGE>   9

                                   SENIOR DEBT PORTFOLIO


                                   By BOSTON MANAGEMENT AND RESEARCH,
                                         as Investment Adviser



                                   By    /s/SCOTT H. PAGE
                                     -------------------------------------------
                                       Name:   Scott H. Page
                                       Title:     Vice President


                                   EATON VANCE SENIOR INCOME TRUST


                                   By EATON VANCE MANAGEMENT
                                         as Investment Adviser



                                   By    /s/SCOTT H. PAGE
                                     -------------------------------------------
                                       Name:   Scott H. Page
                                       Title:     Vice President


                                   UNION BANK OF CALIFORNIA, N.A.



                                   By    /s/RICHARD FAULKNER
                                     -------------------------------------------
                                       Name:   Richard Faulkner
                                       Title:     Vice President


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