The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all products and all products

    FM3 common problems



    Posts : 1
    Join date : 2015-02-07

    FM3 common problems

    Post by timp3 on Sat Feb 07, 2015 2:05 am

    Starting to work on my FM3 ... Stereo indicator stays illuminated . Will the usual update mods fix this problem or is this more related to alignment?


    Posts : 792
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: FM3 common problems

    Post by GP49 on Sat Feb 07, 2015 3:59 pm

    No way of being sure but I suspect something is amiss. Since you don't say what modifications you intend to do, we don't know. Modifications to the audio section only will have no effect on this complaint, of course.

    It is more work, but I like to make sure I have a 100% properly functioning stock unit before doing any modifications. I would align it and bring it to proper operation, first.


    Posts : 88
    Join date : 2014-08-29

    Re: FM3 common problems

    Post by eickmewg on Sat Feb 07, 2015 5:33 pm

    The FM3 assembly manual has the following: "If the STEREOCATOR indicates STEREO on both mono and stereo stations, the 19KC amplifier is oscillating. A rough check of the STEREOCATOR is to disconnect the green wire from eyelet #75 and touch the free end with the finger, which should illuminate the word STEREO. If the STEREOCATOR passes this test, but does no deflect on a known stereo broadcast, check the 6BL8 (tube on the PC 12 board), and also check the continuity of T71 and T72 with an ohmmeter. The resistance of each transformer pin to ground is approximately as follows: #1 pin 0 ohms, #2 pin 40 ohms, #3 pin 10 ohms, #4 pin 100 ohms. The #1 pin is identified on the board by a white mark (the indicator on the top of the transformer) and the pins are numbered clockwise when looking from the bottom of the board." Note that T71 and T72 are both also on the PC 12 board as is the green wire connected to eyelet 75. So, you might try a new 6BL8 tube and check those two transformers on the PC-12 board. That might fix your problem.



    Posts : 21
    Join date : 2010-09-08
    Location : Home

    Re: FM3 common problems

    Post by Dynalover on Sun Mar 01, 2015 7:54 pm

    How did this pan out? As suggested this could be an alignment issue.

    Sponsored content

    Re: FM3 common problems

    Post by Sponsored content

      Current date/time is Thu Jun 21, 2018 2:23 am