THERMO OPTEK CORP
POS AM, 1998-04-10
LABORATORY ANALYTICAL INSTRUMENTS
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        As filed with the Securities and Exchange Commission on 

        April 10, 1998                      Registration No. 333-16017
        --------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION 
                             Washington, DC  20549 
                         _______________________________
                         POST-EFFECTIVE AMENDMENT NO. 2
                             ON FORM S-3 TO FORM S-1
                             Registration Statement
                        Under the Securities Act of 1933
                        ________________________________

                            THERMO OPTEK CORPORATION 
             (Exact name of registrant as specified in its charter) 

                     Delaware                       04-3283973
         (State or other jurisdiction of         (I.R.S. Employer
          incorporation or organization)        Identification No.)
                                 _______________

                              8 East Forge Parkway
                          Franklin, Massachusetts 02038
                                 (508) 553-1700
          (Address, including zip code, and telephone number, including
            area code, of registrant's principal executive offices) 
                                _______________ 

                          Sandra L. Lambert, Secretary 
                            Thermo Optek Corporation 
                         c/o Thermo Electron Corporation
                                81 Wyman Street 
                                 P.O. Box 9046 
                       Waltham, Massachusetts  02254-9046 
                                 (781) 622-1000 
            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

                                _______________ 

                                    Copy to:
                             Seth H. Hoogasian, Esq.
                                General Counsel 
                            Thermo Optek Corporation 
                         c/o Thermo Electron Corporation
                                81 Wyman Street 
                                 P.O. Box 9046 
                       Waltham, Massachusetts  02254-9046 
                                 (781) 622-1000 
                                 _______________

        Approximate date of commencement of proposed sale to the public:
        From time to time after the effective date of this registration
        statement.
PAGE
<PAGE>






        If the only securities being requested on this form are being
        offered pursuant to dividend or interest reinvestment plans,
        please check the following box. [  ]

        If any of the securities being registered on this form are to be
        offered on a delayed or continuous basis pursuant to Rule 415
        under the Securities Act of 1933, other than securities offered
        only in connection with dividend or interest reinvestment plans,
        check the following box. [X] 

        If this form is filed to register additional securities for an
        offering pursuant to Rule 462(b) under the Securities Act of
        1933, check the following box and list the Securities Act
        registration statement number of the earlier effective
        registration statement for the same offering. [  ] 

        If this form is a post-effective amendment filed pursuant to Rule
        462(c) under the Securities Act of 1933,  check the following box
        and list the Securities Act registration statement number of the
        earlier effective  registration statement for the same offering.
        [  ] 

        If delivery of the prospectus is expected to be made pursuant to
        Rule 434, check the following box. [  ] 


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<PAGE>





                   SUBJECT TO COMPLETION, DATED APRIL 10, 1998

        PROSPECTUS 
                                6,481,481 Shares 

                            THERMO OPTEK CORPORATION

                                  Common Stock 

                  This Prospectus relates to the resale of 6,481,481
        shares (the "Shares") of Common Stock, par value $.01 per share
        (the "Common Stock"), of Thermo Optek Corporation ("Thermo Optek"
        or the "Company") issuable upon conversion of $96,250,000
        principal amount of the Company's outstanding 5% Convertible
        Subordinated Debentures due 2000 (the "Debentures").  The
        Debentures are convertible, at the option of the holder (a
        "Selling Shareholder"), at a conversion price of $13.9446 per
        share, subject to adjustment for certain events.   The Shares may
        be offered from time to time in transactions on the American
        Stock Exchange, in negotiated transactions, through the writing
        of options on the Shares, or a combination of such methods of
        sale, at fixed prices that may be changed, at market prices
        prevailing at the time of sale, at prices related to such
        prevailing market prices or at negotiated prices.  Such
        transactions may be effected by the sale of Shares to or through
        broker-dealers, and such broker-dealers may receive compensation
        in the form of discounts, concessions or commissions from the
        sellers and/or the purchasers of the Shares for whom such
        broker-dealers may act as agent or to whom they sell as
        principal, or both (which compensation to a particular
        broker-dealer might be in excess of customary commissions).  The
        sellers of the Shares and any broker-dealer who acts in
        connection with the sale of Shares hereunder may be deemed to be
        "underwriters" as that term is defined in the Securities Act of
        1933, as amended (the "Securities Act"), and any commissions
        received by them and profit on any resale of the Shares as
        principal might be deemed to be underwriting discounts and
        commissions under the Securities Act.  

                                 _______________

        The Common Stock offered hereby involves a high degree of risk. 
                         See "RISK FACTORS" at page 5. 
                                _______________ 

        THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
        SECURITIES AND  EXCHANGE COMMISSION OR ANY STATE SECURITIES
        COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION OR ANY
        STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY
        OF THIS PROSPECTUS.  ANY REPRESENTATION TO THE CONTRARY IS A
        CRIMINAL OFFENSE. 

                          ----------------------------
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<PAGE>






           None of the proceeds from the sale of the Shares by the
        Selling Shareholders will be received by the Company.  The
        Company has agreed to bear all expenses (other than underwriting
        discounts and selling commissions, and fees and expenses of
        counsel or other advisers to the sellers of the Shares) in
        connection with the registration and sale of the Shares being
        registered hereby.  The Company has agreed to indemnify the
        sellers of the Shares against certain liabilities under the
        Securities Act as underwriter or otherwise.

           The Company is a majority-owned subsidiary of Thermo
        Instrument Systems Inc. ("Thermo Instrument"), which is a
        majority-owned subsidiary of Thermo Electron Corporation ("Thermo
        Electron").  The Common Stock is traded on the American Stock
        Exchange under the symbol "TOC."  On April 9, 1998 the reported
        closing price of the Common Stock on the American Stock Exchange
        was $16.625 per share.


                 The date of this Prospectus is April __, 1998.

                                _________________


           No dealer, salesman or other person has been authorized to
        give any information or to make any representations other than
        those contained or incorporated by reference in this Prospectus
        regarding the Company or the offering made by this Prospectus,
        and, if given or made, such information or representations must
        not be relied upon as having been authorized by the Company or by
        any other person.  Unless otherwise noted, all information
        contained in this Prospectus is as of the date of this
        Prospectus.  Neither the delivery of this Prospectus nor any sale
        or distribution and resale made hereunder shall, under any
        circumstances, create any implication that there has been no
        change in the affairs of the Company since the date hereof.  This
        Prospectus does not constitute an offer to sell or a solicitation
        of any offer to buy any security other than the securities
        covered by this Prospectus, nor does it constitute an offer to or
        solicitation of any person in any jurisdiction in which such
        offer or solicitation may not be lawfully made.

                                  _____________











                                        2
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                              AVAILABLE INFORMATION

           The Company is subject to the informational requirements of
        the Securities Exchange Act of 1934, as amended (the "Exchange
        Act"), and in accordance therewith files reports, proxy
        statements and other information with the Securities and Exchange
        Commission (the "Commission").  Such reports, proxy statements
        and other information can be inspected and copied at the public
        reference facilities maintained by the Commission at 450 Fifth
        Street, N.W., Washington, D.C. 20549, and at the following
        Regional Offices of the Commission:  500 West Madison Street,
        Suite 1400, Chicago, Illinois 60661, and 7 World Trade Center,
        Suite 1300, New York, New York 10048.  Copies of such material
        can also be obtained from the Public Reference Section of the
        Commission at 450 Fifth Street, N.W., Washington, D.C. 20549 at
        prescribed rates.  The Commission also maintains a Web site that
        contains reports, proxy and information statements and other
        information regarding registrants that file electronically with
        the Commission, including the Company; the address of such Web
        site is http://www.sec.gov.  The Common Stock of the Company is
        listed on the American Stock Exchange, and the reports, proxy
        statements and other information filed by the Company with the
        Commission can be inspected at the offices of the American Stock
        Exchange, 86 Trinity Place, New York, New York 10006.

           This Prospectus, which constitutes part of a Registration
        Statement filed by the Company with the Commission under the
        Securities Act, omits certain of the information contained in the
        Registration Statement.  Reference is hereby made to the
        Registration Statement and to the exhibits relating thereto for
        further information with respect to the Company and the Shares
        offered hereby.  Statements contained herein concerning
        provisions of documents are necessarily summaries of such
        documents, and each statement is qualified in its entirety by
        reference to the applicable document filed with the Commission.

           The Company undertakes to provide without charge to each
        person to whom a copy of this Prospectus has been delivered, on
        the written or oral request of such person, a copy of any or all
        of the documents that have been or may be incorporated in this
        Prospectus by reference, other than exhibits to such documents
        (unless such exhibits are specifically incorporated by reference
        therein).  Requests for such copies should be directed to:
        Sandra L. Lambert, Secretary, Thermo Optek Corporation, c/o
        Thermo Electron Corporation, 81 Wyman Street, P. O. Box 9046,
        Waltham, Massachusetts 02254-9046 (telephone: (781) 622-1000).








                                        3
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<PAGE>






                                   THE COMPANY

           The Company is a worldwide leader in analytical
        instrumentation based upon energy and light measurements, and
        surface-analysis characterization and preparation.  The Company's
        instruments are used in the elemental and molecular analysis of a
        wide variety of solids, liquids, and gases, as well as in testing
        and fabricating advanced materials..  Serving multibillion-dollar

        markets, the Company provides industry, government, and academia
        with complete solutions to specific analytical problems, moving
        sophisticated analytical technology outside the lab.  The
        Company's instruments are used in virtually every industry for
        research and development, manufacturing, and quality control.
        The Company was incorporated in Delaware in August 1995 as a  
        subsidiary of Thermo Instrument Systems Inc. ("Thermo
        Instrument").  Thermo Instrument is a publicly traded
        majority-owned subsidiary of Thermo Electron Corporation ("Thermo
        Electron"). 

           Unless the context otherwise requires, references in this
        Prospectus to the Company refer to Thermo Optek Corporation and
        its subsidiaries and their predecessors.  As of January 3, 1998,
        Thermo Instrument owned 91% of the Company's outstanding Common
        Stock.  The Company's principal executive offices are located at
        8 East Forge Parkway, Franklin, Massachusetts 02038, and its
        telephone number is (508) 553-1700.



























                                        4
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<PAGE>






                                  RISK FACTORS

           In connection with the "safe harbor" provisions of the
        Private Securities Litigation Reform Act of 1995, the Company
        wishes to caution readers that the following important factors,
        among others, in some cases have affected, and in the future
        could affect, the Company's actual results and could cause its
        actual results in 1998 and beyond to differ materially from those
        expressed in any forward-looking statements made by, or on behalf
        of, the Company.

           Risks Associated with Technological Change, Obsolescence, and
           -------------------------------------------------------------
        the Development and Acceptance of New Products.  The market for
        ----------------------------------------------
        the Company's products is characterized by rapid and significant
        technological change and evolving industry standards.  New
        product introductions responsive to these factors require
        significant planning, design, development, and testing at the
        technological, product, and manufacturing process levels, and may
        render existing products and technologies uncompetitive or
        obsolete.  There can be no assurance that the Company's products
        will not become uncompetitive or obsolete.  In addition, industry
        acceptance of new technologies developed by the Company may be
        slow to develop due to, among other things, existing regulations
        written specifically for older technologies and general
        unfamiliarity of users with new technologies.

           Risks Associated with Acquisition Strategy; No Assurance of a
           -------------------------------------------------------------
        Successful Acquisition Strategy.  The Company's growth strategy
        -------------------------------
        is to supplement its internal growth with the acquisition of
        businesses and technologies that complement or augment the
        Company's existing product lines.  Certain businesses the Company
        has acquired in the past have had low levels of productivity, and
        businesses that the Company may seek to acquire in the future may
        also be marginally profitable or unprofitable.  In order for any
        acquired businesses to achieve the level of profitability desired
        by the Company, the Company must successfully reduce expenses and
        improve market penetration.  No assurance can be given that the
        Company will be successful in this regard.  In addition,
        promising acquisitions are difficult to identify and complete for
        a number of reasons, including competition among prospective
        buyers and the need for regulatory approvals, including antitrust
        approvals.  There can be no assurance that the Company will be
        able to complete pending or future acquisitions.  In order to
        finance any such acquisitions, it may be necessary for the
        Company to raise additional funds either through public or
        private financings.  Any equity or debt financing, if available
        at all, may be on terms which are not favorable to the Company.

           Possible Adverse Effect from Consolidation in the
           -------------------------------------------------
        Environmental Market and Changes in Environmental Regulations.
        -------------------------------------------------------------
        One of the largest markets for the Company's products is
        environmental analysis.  In recent years, there has been a
        contraction in the market for analytical instruments used for

                                        5
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<PAGE>





        environmental analysis.  This contraction has caused
        consolidation in the businesses serving this market.  Further
        consolidation or contraction may have an adverse impact in
        certain of the Company's businesses.  In addition, most air,
        water, and soil analysis is conducted to comply with federal,
        state, local, and foreign environmental regulations.  These
        regulations are frequently specific as to the type of technology
        required for a particular analysis and the level of detection
        required for that analysis.  The Company develops, configures,
        and markets its products to meet customer needs created by
        existing and anticipated environmental regulations.  These
        regulations may be amended or eliminated in response to new
        scientific evidence or political or economic considerations.  Any
        significant change in environmental regulations could result in a
        reduction in demand for the Company's products.

           Possible Adverse Impact of Significant International
           ----------------------------------------------------
        Operations.  Sales outside the United States accounted for
        ----------
        approximately 63% of the Company's revenues in 1997, and the
        Company expects that international sales will continue to account
        for a significant portion of the Company's revenues in the
        future.  Sales to customers in foreign countries are subject to a
        number of risks, including the following:  agreements may be
        difficult to enforce and receivables difficult to collect through
        a foreign country's legal system; foreign customers may have
        longer payment cycles; foreign countries could impose withholding
        taxes or otherwise tax the Company's foreign income, impose
        tariffs, or adopt other restrictions on foreign trade;
        fluctuations in exchange rates may affect product demand and
        adversely affect the profitability in U.S. dollars of products
        and services provided by the Company in foreign markets where
        payment for the Company's products and services is made in the
        local currency; U.S. or foreign export licenses may be difficult
        to obtain; and the protection of intellectual property in foreign
        countries may be more difficult to enforce.  There can be no
        assurance that any of these factors will not have a material
        adverse effect on the Company's business and results of
        operations.

           Competition.  The Company encounters and expects to continue
           -----------
        to encounter intense competition in the sale of its products.
        The Company believes that the principal competitive factors
        affecting the market for its products include product
        performance, price, reliability, and customer service.  The
        Company's competitors include large multinational corporations
        and their operating units, including The Perkin-Elmer Corporation
        and Varian Associates, Inc.  These companies and certain of the
        Company's other competitors have substantially greater financial,
        marketing, and other resources than those of the Company.  As a
        result, they may be able to adapt more quickly to new or emerging
        technologies and changes in customer requirements, or to devote
        greater resources to the promotion and sale of their products
        than the Company.  In addition, competition could increase if new
        companies enter the market or if existing competitors expand

                                        6
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<PAGE>





        their product lines or intensify efforts within existing products
        lines.  There can be no assurance that the Company's current
        products, products under development, or ability to discover new
        technologies will be sufficient to enable it to compete
        effectively with its competitors.

           Risks Associated with Protection, Defense, and Use of
           -----------------------------------------------------
        Intellectual Property.  The Company holds patents relating to
        ---------------------
        various aspects of its products, and believes that proprietary
        technical know-how is critical to many of its products.
        Proprietary rights relating to the Company's products are
        protected from unauthorized use by third parties only to the
        extent that they are covered by valid and enforceable patents or
        are maintained in confidence as trade secrets.  There can be no
        assurance that patents will issue from any pending or future
        patent applications owned by or license to the Company or that
        the claims allowed under any issued patents will be sufficiently
        broad to protect the Company's technology and, in the absence of
        patent protection, the Company may be vulnerable to competitors
        who attempt to copy the Company's products or gain access to its
        trade secrets and know-how.  Proceedings initiated by the Company
        to protect its proprietary rights could result in substantial
        costs to the Company.  There can be no assurance that competitors
        of the Company will not initiate litigation to challenge the
        validity of the Company's patents, or that they will not use
        their resources to design comparable products that do not
        infringe the Company's patents.  There also may be pending or
        issued patents held by parties not affiliated with the Company
        that relate to the Company's products or technologies.  The
        Company may need to acquire licenses to, or contest the validity
        of, any such patents.  There can be no assurance that any license
        required under any such patent would be made available on
        acceptable terms or that the Company would prevail in any such
        contest.  The Company could incur substantial costs in defending
        itself in suits brought against it or in suits in which the
        Company may assert its patent rights against others.  If the
        outcome of any such litigation is unfavorable to the Company, the
        Company's business and results of operations could be materially
        adversely affected.  In addition, the Company relies on trade
        secrets and proprietary know-how which it seeks to protect, in
        part, by confidentiality agreements with its collaborators,
        employees, and consultants.  There can be no assurance that these
        agreements will not be breached, that the Company would have
        adequate remedies for any breach or that the Company's trade
        secrets will not otherwise become known or be independently
        developed by competitors.





                              SELLING SHAREHOLDERS



                                        7
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           The Selling Shareholders currently hold Debentures
        convertible into Shares which are the subject of this Prospectus.
        It is unknown if, when or in what amounts a Selling Shareholder
        may offer Shares for sale and there can be no assurance that the
        Selling Shareholders will sell any or all of the Shares offered
        hereby.

           Because the Selling Shareholders may offer all or some of the
        Shares pursuant to the offering contemplated by this Prospectus,
        and because there are currently no agreements, arrangements or
        understandings with respect to the sale of any of the Shares that
        will be held by the Selling Shareholders after the completion of
        this offering, no estimate can be given as to the amount of the
        Shares that will be held by the Selling Shareholders after
        completion of this offering. To the best of the Company's
        knowledge, none of the Selling Shareholders, other than Mr.
        Robert McCabe, currently owns any shares of Common Stock.

           Other than as a result of the ownership of the Debentures, to
        the best of the Company's knowledge, none of the Selling
        Shareholders other than Mr. Robert McCabe, a Director of the
        Company, had any material relationship with the Company within
        the three year period ending on the date of this Prospectus.

           The names of the Selling Shareholders, the principal amount
        of Debentures held by each of them, and the number of Shares into
        which such Debentures are convertible are set forth below. 



                                                         Number of
                                                        Shares into
                                           Principal       which
                                           Amount of  Debentures are
                Selling Shareholder       Debentures  Convertible (1)
                -------------------       ----------  ---------------

                                                               6,734
           ABN Amro Bank  ................  $100,000
           Bank Julius Baer & Co., Ltd.  . 1,410,000          94,949
           Bank Sarasin et Cie  ..........   500,000          33,670

           Bank Von Ernst and Cie AG  ....    75,000           5,050
           BHF Securities Corporation  ...   300,000          20,202
           Blondell Establishment  .......   200,000          13,468

           Bober & Co.  .................. 9,496,000         639,461
           Boyd & Co.  ................... 1,600,000         107,744
           Brown Brothers Harriman & Co.     110,000           7,407

           Cantrade Private Bank  ........   100,000           6,734
           Cie de Gestion et de Banque
           Gonet SA  .....................    125,000           8,417
           Clariden Bank Zurich  .........    75,000           5,050


                                        8
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           Credit Suisse Zurich  .........    75,000           5,050
                                             850,000          57,239
           Cudd & Co.  ...................
           Darier Hentsch et Cie  ........ 9,530,000         641,750
           Egger & Co.  .................. 1,750,000         117,845

           Forbank & Co.  ................ 4,575,000         308,080
           Gerlach & Co.  ................ 2,340,000         157,575
           Greig Middleton Ltd.  .........     5,000             336

           Gorman & Co.  .................    50,000           3,367
           Hare & Co.  ...................12,938,000         871,245
           J. Romeo & Co.  ...............   745,000          50,168

           Kink & Co.  ...................   100,000           6,734
           Lehman Brothers Inc.  ......... 2,284,000         153,804
           LGT Bank in Lichenstein AG  ...    50,000           3,367

           Loco & Co.  ................... 1,025,000          69,023
           Petronome Corp.  ..............   250,000          16,835

           Prudential Securities              100,000           6,734
           Incorporated  .................
           Swiss Volksbank Switzerland  ..    40,000           2,693
           TFinn & Co.  ..................   920,000          61,952

           Verwaltungs und Privat Bank AG    100,000           6,734
           Zvercher Kantonalbank
           Switzerland  ..................    500,000          33,670
           Akkad & Co.  .................. 5,000,000         336,700

           Alpine & Co.  .................   250,000          16,385
           Artistic Investments Ltd.  ....    90,000           6,060
           Auer & Co.  ...................   800,000          53,872

           Banque San Paolo  .............   500,000          33,670
           Biltrust Ltd.  ................   405,000          27,272
           Booth & Co.  ..................   530,000          35,690

           Bost & Co.  ................... 6,460,000         435,016
           Bridgerope & Co.  ............. 1,585,000         106,734

           C.O. Nominees                      150,000          10,101
           Limited/Chelmsford Essex  .....
           Catamaran & Co.  .............. 1,065,000           71,717
           Comar Inc.  ...................   200,000          13,468

           DeckAnchor & Co.  ............. 2,000,000         134,680
           Fuelship & Co.  ...............   430,000          28,956
           Glyns Nominees Limited  .......   350,000          23,569

           Robert A. McCabe  .............   100,000           6,734



                                        9
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           Merrill Lynch Pierce Fenner &
           Smith Incorporated  ...........    250,000          16,835
                                           3,852,000         259,393
           Muico & Co.  ..................
           Northman & Co.  ...............   580,000          39,057
           Pitt & Co.  ...................   350,000          23,569

           Republic New York Securities
           Corp.  ........................    250,000          16,835
           Salkeld & Co.  ................  2,000,000         134,680
           Tamarack & Co.  ...............  2,430,000         163,636

           Comdisco Foundation  ..........    100,000           6,734
           Hal Kirshner  .................    200,000          13,468
           William Pontikees 1985 Family
           Trust  ........................    100,000           6,734


        (1)       Share amounts set forth in the table do not include
                  fractional amounts which will be cashed out at the time
                  of any conversion of Debentures into Shares.


                                 SALE OF SHARES

           The Company will not receive any of the proceeds from this
        offering.  The Shares offered hereby may be sold from time to
        time by or for the accounts of any of the Selling Shareholders or
        by their pledgees, donees, distributees or transferees or other
        successors in interest to the Selling Shareholders.  The Shares
        may be sold hereunder directly to purchasers by the Selling
        Shareholders in negotiated transactions; by or through brokers or
        dealers in ordinary brokerage transactions or transactions in
        which the broker solicits purchases or block trades in which the
        broker or dealer will attempt to sell the Shares as agent but may
        position and resell a portion of the block as principal;
        transactions in which a broker or dealer purchases as principal
        for resale for its own account; or through underwriters or
        agents.  The Shares may be sold at a fixed offering price, which
        may be changed, at the prevailing market price at the time of
        sale, at prices related to such prevailing market price or at
        negotiated prices.  Any brokers, dealers, underwriters or agents
        may arrange with others to participate in any such transaction
        and may receive compensation in the form of discounts,
        commissions or concessions from the Selling Shareholders and/or
        the purchasers of the Shares.  Each Selling Shareholder will be
        responsible for payment of any and all commissions to brokers.

           The aggregate proceeds to any Selling Shareholder from the
        sale of the Shares offered by a Selling Shareholder hereby will
        be the purchase price of such Shares less any broker's
        commissions.



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           In order to comply with the securities laws of certain
        states, if applicable, the Shares will be sold in such
        jurisdiction only through registered or licensed brokers or
        dealers.  In addition, in certain states the Shares may not be
        sold unless they have been registered or qualified for sale in
        the applicable state or an exemption from the registration or
        qualification requirement is available and is complied with.

           Any Selling Shareholder and any broker-dealer, agent or
        underwriter that participates with the Selling Shareholder in the
        distribution of the Shares may be deemed to be "underwriters"
        within the meaning of the Securities Act, in which event any
        commissions received by such broker-dealers, agents or
        underwriters and any profit on the resale of the Shares purchased
        by them may be deemed to be underwriting commissions or discounts
        under the Securities Act. 

           The Company has been advised that the Selling Shareholders
        may sell Shares from time to time in transactions on the American
        Stock Exchange, in negotiated transactions, through the writing
        of options on the Shares, or a combination of such methods of
        sale, at fixed prices which may be changed, at market prices
        prevailing at the time of sale, at prices related to such
        prevailing market price or at negotiated prices.  The Selling
        Shareholders may effect such transactions by selling the Shares
        to or through broker-dealers, and such broker-dealers may receive
        compensation in the form of discounts, concessions or commissions
        from the Selling Shareholders and/or the purchasers of the Shares
        for whom such broker-dealers may act as agent or to whom they
        sell as principal, or both (which compensation to a particular
        broker-dealer might be in excess of customary commissions).

           The Selling Shareholders and any broker-dealers who act in
        connection with the sale of Shares hereunder may be deemed to be
        "underwriters" as that term is defined in the Securities Act, and
        any commissions received by them and profit on any resale of the
        Shares as principal might be deemed to be underwriting discounts
        and commissions under the Securities Act.  The Company has agreed
        to indemnify the Selling Shareholders against certain
        liabilities, including liabilities under the Securities Act as
        underwriter or otherwise.










                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE



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             The following documents previously filed with the Commission
        by the Company (File No. 1-11757) are hereby incorporated in this
        Prospectus by reference:

             (a)  Annual Report on Form 10-K for the fiscal year ended
                  January 3, 1998; and

             (b)  The description of the Common Stock which is contained
                  in the Company's Registration Statement on Form 8-A
                  filed under the Exchange Act, as such description may
                  be amended from time to time.

             All documents filed by the Company pursuant to Sections
        13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the
        date of this Prospectus and prior to the termination of the
        offering made hereby shall be deemed to be incorporated by
        reference into this Prospectus and to be a part hereof from the
        respective dates of filing of such documents.  Any statement
        contained herein or in a document all or any portion of which is
        incorporated or deemed to be incorporated by reference herein
        shall be deemed to be modified or superseded for purposes of this
        Prospectus to the extent that a statement contained herein or in
        any other subsequently filed document which also is or is deemed
        to be incorporated by reference herein modifies or supersedes
        such earlier statement.  Any statement so modified or superseded
        shall not be deemed, except as so modified or superseded, to
        constitute a part of this Prospectus.  

             The Company will provide without charge to any person to
        whom this Prospectus is delivered, upon the written or oral
        request of such person, a copy of any or all of the foregoing
        documents incorporated herein by reference (other than certain
        exhibits to such documents).  Requests for such copies should be
        directed to Sandra L. Lambert, Secretary, Thermo Optek
        Corporation, c/o Thermo Electron Corporation, 81 Wyman Street,
        P.O. Box 9046, Waltham, Massachusetts 02254-9046 (telephone:
        (781) 622-1000).


                                  LEGAL MATTERS

           Certain legal matters relating to the Shares offered hereby
        have been passed upon for the Company by Seth H. Hoogasian, Esq.,
        General Counsel of Thermo Electron, Thermo Instrument and the
        Company.  As of the date of such opinion, Mr. Hoogasian owned or
        had the right to acquire 6,000 shares of Common Stock, 20,921
        shares of common stock of Thermo Instrument and 118,177 shares of
        common stock of Thermo Electron. 




                                    EXPERTS


                                       12
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<PAGE>





          The       financial  statements of  the  Company    included  in 
        this Prospectus  and the financial statement schedules included  in
        the Registration Statement of which this Prospectus forms a part have
        been  audited  by   Arthur  Andersen   LLP,  independent   public
        accountants, to the extent  and for the  periods as indicated  in
        their report with  respect thereto,  and are  included  herein in
        reliance upon the  authority of  said firm as  experts in  giving
        said reports. 















































                                       13
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<PAGE>






                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

             Item 14.  Other Expenses of Issuance and Distribution.

           The expenses incurred by the Company in connection with the
        issuance and distribution of the securities being registered are
        as follows.  All amounts are estimated except the Securities and
        Exchange Commission registration fee.
                                                           Amount
                                                           ------
           Registration fee - Securities and Exchange      23,324.00
           Commission ...................................         

           Legal fees and expenses ......................  10,000.00
                                                                  
           Accounting fees and expenses .................  10,000.00
                                                                  
           Miscellaneous ................................   6,676.00

                Total ...................................  50,000.00
                                                                  

             Item 15.  Indemnification of Directors and Officers.

             The Delaware General Corporation Law and the Company's
        Certificate of Incorporation and By-Laws limit the monetary
        liability of directors to the Company and to its stockholders and
        provide for indemnification of the Company's officers and
        directors for liabilities and expenses that they may incur in
        such capacities. In general, officers and directors are
        indemnified with respect to actions taken in good faith in a
        manner reasonably believed to be in, or not opposed to, the best
        interests of the Company and, with respect to any criminal action
        or proceeding, actions that the indemnitee had no reasonable
        cause to believe were unlawful.  The Company also has
        indemnification agreements with its directors and officers that
        provide for the maximum indemnification allowed by law.  

             Thermo Electron Corporation has an insurance policy which
        insures the directors and officers of Thermo Electron and its
        subsidiaries, including the Company, against certain liabilities
        which might be incurred in connection with the performance of
        their duties.

             The Selling Shareholders are obligated under the Purchase
        Agreements to indemnify directors, officers and controlling
        persons of the Registrant against certain liabilities, including
        liabilities under the Securities Act.

             Item 16.  Exhibits



                                       14
PAGE
<PAGE>





             See the Exhibit Index included immediately preceding the
        exhibits to this Registration Statement.


             Item 17.  Undertakings.

             (a)  The undersigned Registrant hereby undertakes as
        follows:

                   (1) To file, during any period in which offers or
                       sales are being made, a post-effective amendment
                       to this registration statement:

                       (i)  To include any prospectus required by Section
                            10(a)(3) of the Securities Act of 1933;

                       (ii) To reflect in the prospectus any facts or
                            events arising after the effective date of
                            the registration statement (or the most
                            recent post-effective amendment thereof)
                            which, individually or in the aggregate,
                            represent a fundamental change in the
                            information set forth in the registration
                            statement.  Notwithstanding the foregoing,
                            any increase or decrease in volume of
                            securities offered (if the total dollar value
                            of securities offered would not exceed that
                            which was registered) and any deviation from
                            the low or high end of the estimated maximum
                            offering range may be reflected in the form
                            of prospectus filed with the Commission
                            pursuant to Rule 424(b) if, in the aggregate,
                            the changes in volume and price represent no
                            more than 20 percent change in the maximum
                            aggregate offering price set forth in the
                            "Calculation of Registration Fee" table in
                            the effective registration statement;

                       (iii)To include any material information with
                            respect to the plan of distribution not
                            previously disclosed in the registration
                            statement or any material change to such
                            information in the registration statement.

                            Provided, however, that paragraphs (a)(1)(i)
                       and (a)(1)(ii) do not apply if the information
                       required to be included in a post-effective
                       amendment by those paragraphs is contained in
                       periodic reports filed with or furnished to the
                       Commission by the Registrant pursuant to Section
                       13 or Section 15(d) of the Securities Exchange Act
                       of 1934 that are incorporated by reference in the
                       registration statement.


                                       15
PAGE
<PAGE>





                  (2)  That, for the purpose of determining any liability
                       under the Securities Act of 1933, each such
                       post-effective amendment shall be deemed to be a
                       new registration statement relating to the
                       securities offered therein, and the offering of
                       such securities at that time shall be deemed to be
                       the initial bona fide offering thereof.

                  (3)  To remove from registration by means of a
                       post-effective amendment any of the securities
                       being registered which remain unsold at the
                       termination of the offering.

             (b)  The undersigned Registrant hereby undertakes that, for
        purposes of determining any liability under the Securities Act of
        1933, each filing of the Registrant's annual report pursuant to
        Section 13(a) or Section 15(d) of the Securities Exchange Act of
        1934 (and, where applicable, each filing of an employee benefit
        plan's annual report pursuant to Section 15(d) of the Securities
        Exchange Act of 1934) that is incorporated by reference in this
        registration statement shall be deemed to be a new registration
        statement relating to the securities offered therein, and the
        offering of such securities at that time shall be deemed to be
        the initial bona fide offering thereof.

             (c)  Insofar as indemnification for liabilities arising
        under the Securities Act of 1933 may be permitted to directors,
        officers and controlling persons of the Registrant pursuant to
        the foregoing provisions, or otherwise, the Registrant has been
        advised that in the opinion of the Securities and Exchange
        Commission such indemnification is against public policy as
        expressed in the Act and is, therefore, unenforceable.  In the
        event that a claim for indemnification against such liabilities
        (other than the payment by the Registrant of expenses incurred or
        paid by a director, officer or controlling person of the
        Registrant in the successful defense of any action, suit or
        proceeding) is asserted by such director, officer or controlling
        person in connection with the securities being registered, the
        Registrant will, unless in the opinion of its counsel the matter
        has been settled by controlling precedent, submit to a court of
        appropriate jurisdiction the question whether such
        indemnification by it is against public policy as expressed in
        the Act and will be governed by the final adjudication of such
        issue.











                                       16
PAGE
<PAGE>




                                   SIGNATURES

             Pursuant to the requirements of the Securities Act of 1933,
        the Registrant has duly caused this Post-Effective Amendment No.
        2 on Form S-3 to Registration Statement on Form S-1 to be signed
        on its behalf by the undersigned, thereunto duly authorized, in
        the City of Franklin, Commonwealth of Massachusetts, on this 10th
        day of April, 1998.

                                           THERMO OPTEK CORPORATION

                                           By:  /s/ Robert J. Rosenthal
                                               ------------------------
                                                Robert J. Rosenthal
                                                President and Chief
                                                Executive Officer

             Pursuant to the requirements of the Securities Act of 1933,
        this Post-Effective Amendment No. 2 on Form S-3 to Registration
        Statement on Form S-1 has been signed by the following persons in
        the capacities and on the dates indicated.

          Signature                    Title             Date
          ---------                    -----             ----
                                                             
         /s/ Robert J. Rosenthal    President, Chief   April 10, 1998
        ------------------------    Executive Officer
        Robert J. Rosenthal         and Director (Principal
                                    Executive Officer)

        John N. Hatsopoulos*        Chief Financial    April 10, 1998
        -------------------------   Officer and Senior Vice President
        John N. Hatsopoulos         (Principal Financial Officer)

        Paul F. Kelleher*           Chief Accounting   April 10, 1998
        -------------------------   Officer (Principal
        Paul F. Kelleher            Accounting Officer)

        Earl R. Lewis*              Chairman of the    April 10, 1998
        ---------------------       Board and Director
        Earl R. Lewis               

        Dr. George N. Hatsopoulos*  Director           April 10, 1998
        --------------------------
        Dr. George N. Hatsopoulos

        Stephen R. Levy             Director           April   , 1998
        --------------------------                           --
        Stephen R. Levy

        Robert A. McCabe*           Director           April 10, 1998
        --------------------
        Robert A. McCabe

        Arvin H. Smith*             Director           April 10, 1998
        -----------------------
        Arvin H. Smith








                                       17
PAGE
<PAGE>





        *    The undersigned Sandra L. Lambert, by signing her name
        hereto, does hereby execute this Post-Effective Amendment No. 2
        on Form S-3 to Registration Statement on Form S-1 on behalf of
        each of the above-named persons pursuant to powers of attorney
        executed by such persons and filed with the Securities and
        Exchange Commission.

                                           /s/ Sandra L. Lambert
                                           ---------------------
                                           Sandra L. Lambert
                                           Attorney-in-Fact













































                                       18
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<PAGE>






                                  EXHIBIT INDEX


         Exhibit                  Description of Exhibit
         -------                  ----------------------
           No.
           ---
              4   Specimen Common Stock Certificate (filed as Exhibit
                  4 to the Registrant's Registration Statement on Form
                  S-1 [Registration No. 333-3630]  and incorporated
                  herein by reference).

              5   Opinion of Seth H. Hoogasian, Esq. (previously
                  filed)
            23.1  Consent of Arthur Andersen LLP
            23.2  Consent of Seth H. Hoogasian, Esq. (contained in
                  Exhibit 5)






        AA980390006
































                                       19
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<PAGE>





                                                             Exhibit 23.1



                    Consent of Independent Public Accountants
                    -----------------------------------------


        To Thermo Optek Corporation:

            As independent public accountants, we hereby consent to the
        incorporation by reference of our report dated February 17, 1998,
        incorporated by reference in this registration statement and to
        all references to our firm included in or made a part of this
        registration statement on Form S-3.


                                                    Arthur Andersen LLP


        Boston, Massachusetts
        April 7, 1998





































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