EXHIBIT 4.06

                                                               CUSIP 023139 AB 4
                                                               SEE REVERSE FOR
                                   AMBAC                     CERTAIN DEFINITIONS
                                   INC.
                                   7 1/2% DEBENTURE DUE 2023
 

   AMBAC INC., a Delaware corporation (herein called the "Company", which term
   includes any successor corporation under the Indenture hereinafter referred
   to), for value received, hereby promises to pay to



  7 1/2%                                                                  7 1/2%
  DUE 2023                                                              DUE 2023

 
   ,or registered assigns, the principal sum of                          DOLLARS

on May 1, 2023 and to pay interest thereon from May 1, 1993 or from the most
recent Interest Payment Date to whIch interest has been paid or duly provided
for, semi-annually in arrears on May 1 and November 1, 1993 at the rate of 71/2%
per annum, until the principal hereof is paid or made available for payment .
The Interest so payable, and punctually paid or duly provided for, on any
Interest Payment Date will, as provided In such indenture, be paid to the Person
in whose name this Security  (or one or more Predecessor Securities) is
registered at the close of business on the Regular Record Date for such
interest, which shall be the April 15 or October 15 (whether or not a Business
Day), as the case may be, next preceding such Interest Payment Date.  Any such
interest not punctually paid or duly provided for will forthwith cease to be
payable to the Person in whose name this Security (or one or more Predecessor
Securities) is registered on such Regular Record Date and may either be paid to
the Person in whose name this Security (or one or more Predecessor Securities)
is registered at the close of business on a Special Record Date for the payment
of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be
given to Holders of Securities of this series not more than 15 and not less than
10 days prior to such Special Record Date, or be paid at any time in any other
lawful manner not inconsistent with the requirements of any securities exchange
on which such Securities may be listed, as more fully provided in the Indenture.
Each payment of Interest hereon shall include interest accrued from and
including the preceding Interest Payment Date or the date of issuance, as the
case may be, to and excluding the relevant Interest Payment Date or' Maturity,
as the case may be.

        Payment of the principal of and interest on this Security will be made
        at the office or agency of the Company maintained for that purpose in
        The City and State of New York, in such coin or currency of the United
        States of America as at the time of payment is legal tender for payment
        of public and private debts, provided, however, that at the option of
        the Company payment of interest may be made by check mailed to the
        address of the Person entitled thereto as such address shall appear in
        the Security Register.

        Reference is hereby made to the further provisions of this Security set
        forth on the reverse hereof, which further provisions shall for all
        purposes have the same effect as if set forth at this place.

        Unless the certificate of authentication hereon has been executed by the
        Trustee referred to on the reverse hereof by manual signature, this
        Security shall not be entitled to any benefit under the indenture or be
        valid or obligatory for any purpose.

        IN WITNESS WHEREOF, the Company has caused this instrument to be duly
        executed under its corporate seal.


Dated:
 
                                                                                
        TRUSTEES CERTFICATE OF AUTHENTICATION                                     
        This in one of the Securities of the                                      
        series designated therein referred to in                                  
        the within-mentioned indenture.                                              AMBAC INC.                 
                                                                                                                  
         THE CHASE MANHATTAN BANK (NATIONAL ASSOCIATION),                            Attest:                 By: 
                                             as Trustee
 
By:                                                                                  By: /s/ Richard Gross    /s/ Phillip Lassiter
                                                                                     SENIOR VICE PRESIDENT    CHAIRMAN OF THE BOARD,
                                  Authorized Officer                                    AND SECRETARY         PRESIDENT, AND CHIEF
                                                                                                              EXECUTIVE OFFICER

 

 
                                   AMBAC INC.
                                        
                            71/2% DEBENTURE DUE 2023
- --------------------------------------------------------------------------------
                                        
  This Security is one of a duly authorized issue of securities of the Company
(herein called the "Securities"), issued and to be issued in one or more series
under an Indenture, dated as of August 1, 1991 as it may be supplemented from
time to time (herein called the "Indenture"), between the Company and The Chase
Manhattan Bank (National Association). Trustee (herein called the "Trustee",
which term includes any successor trustee under the Indenture with respect to
the series of which this Security is a part), to which Indenture reference is
hereby made for a statement of the respective rights, limitations of rights,
duties and immunities thereunder of the Company, the Trustee and the Holders of
the Securities and of the terms upon which the Securities are, and are to be
authenticated and delivered. This Security is one of the series designated on
the face hereof, limited in aggregate principal amount to $75,000,000.

 The Securities of this series may not be redeemed prior to Maturity.

 The Securities of this series are not subject to the operation of any sinking
fund.

  If an Event of Default with respect to Securities of this series shall occur
and be continuing, the principal of the Securities of this series may be
declared due and payable in the manner and with the effect provided in the
Indenture.

  The Indenture contains provisions for defeasance at any time of (a) the entire
indebtedness of the Company on this Security and (b) certain restrictive
covenants and the related defaults and Events of Default applicable to the
Company, in either case upon compliance by the Company with certain conditions
set forth therein, which provisions apply to this Security.

  The indenture permits, with certain exceptions as therein provided, the amend-
ment thereof and the modification of the rights and obligations of the Company
and the rights of the Holders of the Securities of each series to be affected
under the Indenture at any time by the Company and the Trustee with the consent
of the Holders of not less than a majority in principal amount of all
Outstanding Securities to be so affected. The Indenture also contains provisions
permitting the Holders of not less than a majority in principal amount of the
Outstanding Securities, on behalf of the Holders of all Outstanding Securities,
to waive compliance by the Company with certain provisions of the Indenture, and
contains provisions permitting the Holders of not less than a majority in
principal amount, in certain instances of the Outstanding Securities of
individual series and in other instances of all Securities at the time
Outstanding to waive on behalf of all of the Holders of Securities of such
individual series or of the Holders of all Securities at the time Outstanding,
as the case may be, certain past defaults under the Indenture and their
consequences. Any such consent or waiver by the Holder of this Security shall be
conclusive and binding upon such Holder and upon all future Holders of this
Security and of any Security issued upon the registration of transfer hereof or
in exchange hereof or in lieu hereof, whether or not notation of such consent or
waiver is made upon this Security.

  No reference herein to the Indenture and no provision of this Security or of
the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay or make provision as provided in the
Indenture for the payment of the amount of principal of and interest on this
Security herein provided and at the times, place and rate, and in the coin or
currency herein prescribed.

  As provided in the Indenture and subject to certain limitations therein and
herein set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office or agency of the Company in any place where the principal of and interest
on this Security are payable, duly endorsed by, or accompanied by a written
instrument of transfer in form satisfactory to the Company and the Security
Registrar duly executed by, the Holder hereof or his attorney duly authorized in
writing, and thereupon one or more new Securities of this series, of authorized
denominations and for the same aggregate principal amount, will be issued to the
designated transferee or transferees.

  The Securities of this series are issuable only in registered form without
coupons in denominations of $1,000 and any integral multiple thereof. As
provided in the Indenture and subject to certain limitations therein set forth,
Securities of this series are exchangeable for a like aggregate principal amount
of Securities of this series of a different authorized denomination, as
requested by the Holder surrendering the same.

  No service charge shall be made for any such registration of transferor
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

  Prior to due presentment of this Security for registration of transfer, the
Company, the Trustee and any agent of the Company or the Trustee may treat the
Person in whose name this Security is registered as the owner hereof for all
purposes, whether or not this Security be overdue, and neither the Company, the
Trustee nor any such agent shall be affected by notice to the contrary.

  All terms used in this Security that are defined in the Indenture shall have
the meanings assigned to them in the Indenture.

- --------------------------------------------------------------------------------

                                 ABBREVIATIONS
                                        
   The following abbreviations, when used in the inscription on the face of this
instrument, shall be construed as though they were written out in full according
to applicable laws or regulations.

 
                                                              
   TEN COM -- as tenants in common                               UNIF GIFT MIN ACT --_____________________ Custodian ______________
   TEN ENT -- as tenants by the entiretes                                                    (Cust)                       (Minor)
   JT TEN  -- as joint tenants with right                                                      Under Uniform Gifts to Minors Act
              of survivorship and not as tenants in common                                             ____________________
                                                                                                             (State)
 
 
    Additional abbreviations may also be used though not in the above list,



      FOR VALUE RECEIVED, the undersigned hereby sell(s). assign(s) and 
                               transfer(s) unto


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        IDENTIFYING NUMBER OF ASSIGNEE



    Please print or type name and address, including zip code, of assignee


the within Security and all rights thereunder, irrevocably constituting and
appointing

to transfer said Security on the books of the Company, with full power of
substitution in the premises.


Dated ___________
SIGNATURE GUARANTEED

                                         NOTICE The signature to this assignment
                                                must correspond with the name as
                                                it appears upon the face of the
                                                within Security in every
                                                particular, without alteration
                                                or enlargement or any change
                                                whatsoever.