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    Help identify mods st70 (pic)…

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    opti-mos pat

    Posts : 13
    Join date : 2010-10-19

    Help identify mods st70 (pic)…

    Post by opti-mos pat on Thu Nov 04, 2010 1:41 pm

    I just picked up this amp about a month or so ago and I’m new to tube amps….. I wanted to listen to it before I start playing with it…. Anyway I finally got to look at what was done to it, other then what the guy that sold it to me said it had… I see that it has the cap board by SDS and an upgraded PT and the old Dynaco OPT with the cloth leads …. VTA driver board…. New input/output terminals...Power cord with the ground attached to the chassis? (No hum at all) I thought I read somewhere not to use that ground wire?

    Now, I want to put the triode/pentode switches and what I need to know is….Can you tell if this amp is wired in pentode mode or is it wired in triode mode by looking at the pics? Can I just use Bob’s instructions to install the switches?

    Do you see anything else? Are there some other things you would change by looking at the pics?
    Can you tell if he used good caps/parts?

    http://i161.photobucket.com/albums/t234/c4pc/Dynaco/FILE0336.jpg

    Bob Latino
    Admin

    Posts : 2377
    Join date : 2008-11-27
    Location : Massachusetts

    Re: Help identify mods st70 (pic)…

    Post by Bob Latino on Thu Nov 04, 2010 2:07 pm

    [quote="opti-mos pat"]I just picked up this amp about a month or so ago and I’m new to tube amps….. I wanted to listen to it before I start playing with it…. Anyway I finally got to look at what was done to it, other then what the guy that sold it to me said it had… I see that it has the cap board by SDS and an upgraded PT and the old Dynaco OPT with the cloth leads …. VTA driver board…. New input/output terminals...Power cord with the ground attached to the chassis? (No hum at all) I thought I read somewhere not to use that ground wire?

    Now, I want to put the triode/pentode switches and what I need to know is….Can you tell if this amp is wired in pentode mode or is it wired in triode mode by looking at the pics? Can I just use Bob’s instructions to install the switches?

    Do you see anything else? Are there some other things you would change by looking at the pics?
    Can you tell if he used good caps/parts?

    Hi,

    You have a nice, practically new amp. A new power transformer, an SDS quad cap replacement board, new ceramic sockets, all new wiring, new input and output jacks and best of all > a VTA driver board. The only thing I can see is that the rectifier tube socket was put in backwards but it has been wired up properly. To answer your other question, the amp right now is wired in pentode ultralinear and not triode.

    Triode/pentode switches would be a nice addition to allow the amp to operate in both modes. Another thing is that the VTA driver board has the stock main coupling capacitors and probably the stock power supply caps. You may want to upgrade to the coupling caps to Russian PIO and the stock power supply caps from 88 uF to 334 uF.

    By upgrading the amp with the triode/pentode switches and better capacitors, you would have an amp that is basically the equivalent of the ST-70 kits that I sell.

    Bob

      Current date/time is Wed Sep 28, 2016 10:30 am