<PAGE>

                                                                   EXHIBIT 10.B1

                    AMENDMENT dated as of July 15, 1999 (this "Amendment"), to
               the 5-Year Revolving Credit Agreement dated as of November 20,
               1997 (the "Credit Agreement"), among PP&L, INC. ("PPL"), a
               Pennsylvania corporation and PP&L CAPITAL FUNDING, INC., a
               Delaware corporation ("Finance Co."), as Borrowers (the
               "Borrowers"); PP&L RESOURCES, INC., a Pennsylvania corporation
               ("Resources"), as guarantor of the obligations of Finance Co.
               thereunder; the banks from time to time party thereto (the
               "Banks") and THE CHASE MANHATTAN BANK, a New York banking
               corporation, as fronting bank, as collateral agent, and as agent
               for the Banks to the extent and in the manner provided in Section
               8 therein (in such capacity, the "Agent").

          WHEREAS, the Borrowers have requested that the Banks amend certain
provisions of the Credit Agreement as set forth herein;

          WHEREAS, the Banks are willing, on the terms, subject to the
conditions and to the extent set forth below, to provide such amendments; and

          WHEREAS, capitalized terms used and not otherwise defined herein shall
have the meanings assigned to them in the Credit Agreement.

          NOW, THEREFORE, in consideration of the premises and the agreements,
provisions and covenants herein contained, the parties hereto hereby agree, on
the terms and subject to the conditions set forth herein, as follows:

          SECTION 1.  Amendment to Credit Agreement.  Section 1.2 of the Credit
                      -----------------------------
Agreement is amended by replacing the amount "$500,000" contained in such
section with the amount "$1,000,000".

          SECTION 2.  Amendment to Credit Agreement.  Subsection (a) of Section
                      -----------------------------
1.4 of the Credit Agreement is amended by replacing the first sentence with the
following:

     "The outstanding principal balance of each Loan shall be due and payable by
     the Borrower to which such Loan was made on the Expiry Date."

          SECTION 3.  Amendment to Credit Agreement.  Section 3.4 is amended by
                      -----------------------------
replacing such section with the following:
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     "3.4  Net Payments.  All payments under this Agreement shall be made
           ------------
     without set-off or counterclaim and in such amounts as may be necessary in
     order that all such payments of principal and interest in connection with
     Loans (after deduction or withholding for or on account of (i) any present
     or future taxes, levies, imposts, duties or other charges of whatsoever
     nature imposed by any government or any political subdivision or taxing
     authority thereof, excluding any tax on or measured by the net income of a
     Bank pursuant to the income tax laws of the jurisdiction where such Bank's
     principal or lending office is located or in which such Bank maintains a
     place of business (all such non-excluded taxes, levies, imposts, duties or
     other charges, the "Taxes") and (ii) any taxes on or measured by the net
     income payable by any such Bank with respect to the amount by which the
     payments required to be made by this (S) 3.4 exceed the amount otherwise
     specified to be paid under this Agreement) shall not be less than the
     amounts otherwise specified to be paid under this Agreement; and the
     Borrowers further agree to pay and to save the Agent, the Fronting Bank and
     the Banks (and any participant, to the extent provided in Section
     10.6(b)(B)) harmless, on an after-tax basis, from all liability for Taxes
     on or in connection with Loans or any payments thereunder, and any
     interest, penalties or additions with respect thereto, provided, however,
                                                            -----------------
     that such interest, penalties and additions are not a result of any action,
     omission or failure to act on the part of the Agent, the Fronting Bank or
     the Banks.  A certificate as to any additional amounts payable to any Bank
     under this (S) 3.4 submitted to the applicable Borrower by such Bank shall
     show in reasonable detail the amount payable and the calculations used to
     determine such amount and shall, absent manifest error, be final,
     conclusive and binding upon all parties hereto.  With respect to each
     deduction or withholding for or on account of any Taxes, the applicable
     Borrower shall promptly furnish to each Bank such certificates, receipts
     and other documents as may be required (in the judgment of such Bank) to
     establish any tax credit to which such Bank may be entitled."

          SECTION 4.  Amendment to Credit Agreement.  Subsection (a) of each of
                      -----------------------------
Section 5.1A and Section 5.1B of the Credit Agreement is amended by replacing
the words "Price Waterhouse" with "PricewaterhouseCoopers".

          SECTION 5.  Amendment to Credit Agreement.  Section 7.6A to the Credit
                      -----------------------------
Agreement is amended by replacing the words "Regulations G, U or X" contained in
such Section with "Regulation U or X".

          SECTION 6.  Amendment to Credit Agreement.  Section 7.9A of the Credit
                      -----------------------------
Agreement is amended by replacing such section with the following:

     "7.9A  Subsidiaries.  The assets of all Subsidiaries of PPL, excluding
            ------------
     intangible transition property created under the
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                                                                               3

     Pennsylvania Electricity Generation Customer Choice and Competition Act
     held by PP&L Transition Bond Company LLC, a subsidiary of PPL, or any
     similar special purpose company organized for the purpose of issuing bonds
     payable from revenues associated with such transition property, do not
     comprise in the aggregate more than 35% of the total consolidated assets of
     PPL."

          SECTION 7.  Amendment to Credit Agreement.  Section 7.11A of the
                      -----------------------------
Credit Agreement is amended by replacing such section with the following:

     "7.11A  Public Utility Holding Company Act.  PPL is not a "holding company"
             ----------------------------------
     within the meaning of the Public Utility Holding Company Act of 1935, as
     amended."

          SECTION 8. Amendment to Credit Agreement.  Section 10.1 of the Credit
                     -----------------------------
Agreement is amended by deleting the definition of "364-Day Agreement".

          SECTION 9.  Amendment to Credit Agreement.  Section 10.1 of the Credit
                      -----------------------------
Agreement is amended by replacing the definition of "Bank" with the following:

     "'Bank' shall mean each Person listed on Schedule I hereto and any other
       ----
     Person that shall have become a party hereto as a result of an assignment
     pursuant to Section 10.6(b)(A) hereto, other than any such Person that
     ceases to be a party hereto as a result of an assignment pursuant to
     Section 10.6(b)(A) hereto."

          SECTION 10.  Amendment to Credit Agreement.  Section 10.1 of the
                       -----------------------------
Credit Agreement is amended by replacing the definition of "Commitment" with the
following:

     "'Commitment', for each Bank, shall mean the amount specified opposite its
       ----------
     name on Schedule I hereto or in the assignment pursuant to which such Bank
     shall have assumed its Commitment, as applicable, such Commitment to be
     reduced by the amount of any reduction thereto effected pursuant to (S)
     1.7, (S) 6 and/or (S) 10.6(b)(A)."

          SECTION 11.  Amendment to Credit Agreement.  Subsection (i) of the
                       -----------------------------
definition of "Indebtedness" contained in Section 10.1 of the Credit Agreement
is amended by replacing the parenthetical with the following:

     "(the amount of any such obligation to be the net amount that would be
     payable upon the acceleration, termination or liquidation thereof)"

          SECTION 12.  Amendment to Credit Agreement.  Section 10.1 of the
                       -----------------------------
Credit Agreement is amended by adding the following
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                                                                               4

language to subsection (a) of the definition of "Interest Period" after the
words "on the date of such Loan":

     "or on the last day of the most recent Interest Period applicable thereto"

          SECTION 13. Amendment to Credit Agreement.  Section 10.1 of the Credit
                      -----------------------------
Agreement is amended by replacing the definition of "Non-Recourse Indebtedness
of PPL" with the following:

     "'Non-Recourse Indebtedness of PPL' shall mean (a) indebtedness that is
       --------------------------------
     nonrecourse to PPL or any of its Subsidiaries and (b) any transition bonds
     issued by PP&L Transition Bond Company LLC, a subsidiary of PPL, or any
     similar special purpose company organized for the purpose of issuing bonds
     payable from revenues associated with intangible transition property
     created under the Pennsylvania Electricity Generation Customer Choice and
     Competition Act or other assets of PP&L Transition Bond Company LLC or any
     such other special purpose company, provided that (i) such bonds are
                                         --------
     nonrecourse to PPL or any of its subsidiaries (other than PP&L Transition
     Bond Company LLC or any such other special purpose company) and (ii) the
     aggregate amount of such transition bonds shall not exceed $2,850,000,000."

          SECTION 14.  Amendment to Credit Agreement.  Section 10.1 of the
                       -----------------------------
Credit Agreement is amended by replacing the definition of "Non-Recourse
Indebtedness of Resources" with the following:

     "'Non-Recourse Indebtedness of Resources' shall mean (a) indebtedness that
       --------------------------------------
     is nonrecourse to Resources, either Borrower or any of PPL's Subsidiaries
     and (b) any transition bonds issued by PP&L Transition Bond Company LLC, a
     subsidiary of PPL, or any similar special purpose company organized for the
     purpose of issuing bonds payable from revenues associated with intangible
     transition property created under the Pennsylvania Electricity Generation
     Customer Choice and Competition Act or other assets of PP&L Transition Bond
     Company LLC or any such other special purpose company, provided that (i)
                                                            --------
     such bonds are nonrecourse to PPL or any of its subsidiaries (other than
     PP&L Transition Bond Company LLC or any such other special purpose company)
     and (ii) the aggregate amount of such transition bonds shall not exceed
     $2,850,000,000."

          SECTION 15.  Amendment to Credit Agreement.  Section 10.6(b)(A) of the
                       -----------------------------
Credit Agreement is amended by deleting clause (iii) of the proviso in its
entirety and then renumbering clause (iv) to be clause (iii).
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                                                                               5

          SECTION 16.  Amendment to Credit Agreement.  Section 10.6(b)(B) of the
                       -----------------------------
Credit Agreement is amended by replacing the proviso contained in the last
sentence of such section with the following:

     "provided that such participant shall be entitled to receive additional
      --------
     amounts under (S)(S) 1.8, 2.5 and 3.4 on the same basis as if it were a
     Bank but in no case shall be entitled to any amount greater than would have
     been payable had the Bank not sold such participations."

          SECTION 17.  Representations and Warranties.  The Borrowers and
                       ------------------------------
Resources hereby represent and warrant to each Bank, on and as of the date
hereof, and after giving effect to this Amendment, that:

          (a) the representations and warranties set forth in Sections 7.A and
     7.B of the Credit Agreement are true and correct in all material respects
     on and as of the date hereof, except to the extent such representations and
     warranties relate to an earlier date; and

          (b) no Default or Event of Default has occurred and is continuing.

          SECTION 18.  Effectiveness.  The amendments to the Credit Agreement
                       -------------
set forth in this Amendment shall become effective only upon receipt by the
Agent of duly executed counterparts hereof which, when taken together, bear the
authorized signatures of the Borrowers, Resources and the Required Banks.

          SECTION 19.  Governing Law.  THIS AMENDMENT SHALL BE CONSTRUED IN
                       -------------
ACCORDANCE WITH AND GOVERNED BY THE LAW OF THE STATE OF NEW YORK.

          SECTION 20.  Counterparts.  This Amendment may be executed in any
                       ------------
number of counterparts, each of which shall be an original but all of which,
when taken together, shall constitute but one instrument.  Delivery of an
executed counterpart of a signature page of this Amendment by facsimile
transmission shall be as effective as delivery of a manually executed
counterpart of this Amendment.

          SECTION 21.  Expenses.  The Borrowers agree to pay all expenses
                       --------
incurred by the Agent in connection with the preparation, execution and delivery
of this Amendment, including the fees, charges and disbursements of counsel.

          SECTION 22.  Headings.  Section headings used herein are for
                       --------
convenience of reference only, are not part of this
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                                                                               6

Amendment and are not to affect the construction of, or to be taken into
consideration in interpreting, this Amendment.

          SECTION 23.  EFFECT OF THIS AMENDMENT GENERALLY.  Except as expressly
                       ----------------------------------
set forth herein, this Amendment shall not by implication or otherwise limit,
impair, constitute a waiver of, or otherwise affect the rights and remedies of
the Banks under the Credit Agreement or any other Loan Document, and shall not
alter, modify, amend or in any way affect any of the terms, conditions,
obligations, covenants or agreements contained in the Credit Agreement or any
other Loan Document, all of which are ratified and affirmed in all respects and
shall continue in full force and effect.  Nothing herein shall be deemed to
entitle the Borrowers to a consent to, or a waiver, amendment, modification or
other change of, any of the terms, conditions, obligations, covenants or
agreements contained in the Credit Agreement or any other Loan Document in
similar or different circumstances.  This Amendment shall apply and be effective
only with respect to the provisions of the Credit Agreement specifically
referred to herein.

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


                              PP&L INC.,

                              By: /s/ James E. Abel
                                  -------------------------
                                  Name:  James E. Abel
                                  Title: Vice President-
                                   Finance and Treasurer


                              PP&L CAPITAL FUNDING, INC.,

                              By: /s/ Russell R. Clelland
                                  -------------------------
                                  Name:  Russell R. Celland
                                  Title: Manager-Finance

                              PP&L RESOURCES, INC.,

                              By: /s/ James E. Abel
                                  -------------------------
                                  Name:  James E. Abel
                                  Title: Vice President-
                                   Finance and Treasurer
<PAGE>

                                                                               7

                              THE CHASE MANHATTAN BANK,
                              individually and as
                              Agent and Fronting Bank,

                              By: /s/ Jaimin Patel
                                  --------------------------
                                  Name:  Jaimin Patel
                                  Title: Vice President
<PAGE>

                              CITIBANK, N.A.,

                              By: /s/ Robert J. Harrity, Jr
                                  --------------------------
                                  Name:  Robert J. Harrity, Jr.
                                  Title: Managing Director


                              THE BANK OF NEW YORK,

                              By: /s/ John N. Watt
                                  --------------------------
                                  Name:  John N. Watt
                                  Title: Vice President


                              THE BANK OF NOVA SCOTIA

                              By: /s/ J. Alan Edwards
                                  --------------------------
                                  Name:  J. Alan Edwards
                                  Title: Authorized Signatory


                              CREDIT SUISSE FIRST BOSTON,

                              By: /s/ Douglas E. Maher
                                  --------------------------
                                  Name:  Douglas E. Maher
                                  Title: Vice President


                              By: /s/ James P. Moran
                                  --------------------------
                                  Name:  James P. Moran
                                  Title: Director


                              DEUTSCHE BANK AG, NEW YORK BRANCH
                              and/or CAYMAN ISLANDS BRANCH,

                              By: /s/
                                  --------------------------
                                  Name:
                                  Title:
<PAGE>

                              THE FIRST NATIONAL BANK OF CHICAGO,

                              By: /s/ George R. Schanz
                                  --------------------------
                                  Name:  George R. Schanz
                                  Title: First Vice President


                              FIRST UNION NATIONAL BANK,

                              By: /s/ Michael J. Kolosowsky
                                  --------------------------
                                  Name:  Michael J. Kolosowsky
                                  Title: Vice President


                              THE FUJI BANK, LIMITED, NEW YORK BRANCH

                              By: /s/
                                  --------------------------
                                  Name:
                                  Title:


                              MELLON BANK, N.A.,

                              By: /s/ Mark W. Rogers
                                  --------------------------
                                  Name:  Mark W. Rogers
                                  Title: Vice President


                              NATIONSBANK, N.A.,

                              By: /s/ Michael R. Williams
                                  --------------------------
                                  Name:  Michael R. Williams
                                  Title: Managing Director


                              TORONTO DOMINION (TEXAS), INC.,

                              By: /s/ Alva J. Jones
                                  -------------------------
                                  Name: Alva J. Jones
                                  Title: Vice President