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 Tubes4hifi.com products and all Dynakitparts.com products


    Another Stereo 70 rebuild

    Share

    Donkeyshins

    Posts : 19
    Join date : 2011-07-18

    Another Stereo 70 rebuild

    Post by Donkeyshins on Mon Dec 30, 2013 3:14 pm

    I picked up a factory-wired Stereo 70 (along with a Fisher FM-50B tuner and a matching factory-wired Dynaco PAS-3) last summer from Craigslist for a too-good-to-pass-up price.  I promptly flipped the Fisher and PAS-3 as I did not need them, but I did need the money to fund the restoration of the Stereo 70 (when factoring everything in, the amp and restoration was free and I still made about $150).  The chassis, transformers, tube sockets, power tubes and rectifier were retained while the remaining parts were binned or (7199) sold.  The power supply, bias and output circuits are more-or-less unchanged from stock (albeit with an 80/40/30/20 power supply cap, better X1/Y2 death caps, Ohmite wirewound power resistors and a CL-90 for slow turn-on and slight reduction in line voltage).  The driver circuit was replaced with a DIYTube Stereo 70 circuit (it was pretty much a coin toss between this and the VTA board - if I ever get another Stereo 70, I'll try the VTA driver circuit).  Coupling caps are Russian K40Y PIO and Orange Drops, while resistors are a mix of Kiwame and Takman carbon films.  Phase splitter tubes are RCA black-plate 12AU7s and the driver tube is a triple-mica RCA 5751.

    Oh, and my wife bought me a Triode PA060 power transformer for Christmas, but it hasn't arrived yet, so that'll be added shortly.

    Here's how it arrived:





    This is during smoke testing:



    And here it is with a machined cover over the driver board and with a new set of Golden Lion KT77s:



    I still would like to replace the front RCA jacks and figure out a better solution for the bias measurements than the existing front-mounted octal tubes. Perhaps something with three probe sockets on each side? However, for now, I'm happy with the results and it provides a good counterpoint to my Stereo 35.

    -D

    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Another Stereo 70 rebuild

    Post by corndog71 on Wed Jan 01, 2014 12:09 pm

    That cover for the driver board looks great! Nicely done! You might want to consider getting the better power tranny from dynakitparts. The stock one doesn't leave a lot of headroom in certain areas.

    Donkeyshins

    Posts : 19
    Join date : 2011-07-18

    Re: Another Stereo 70 rebuild

    Post by Donkeyshins on Wed Jan 01, 2014 4:08 pm

    corndog71 wrote:That cover for the driver board looks great!  Nicely done!  You might want to consider getting the better power tranny from dynakitparts.  The stock one doesn't leave a lot of headroom in certain areas.

    Funny you should say that.  Guess what my wife got me for Christmas?



    -D

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Another Stereo 70 rebuild

    Post by tubes4hifi on Sun Jan 05, 2014 12:54 am

    Donkeyshins,
    hey, since that driver board is above the chassis, you would have room for my new bias test jacks,
    see on the right side of my webpage here: http://tubes4hifi.com/MK3.htm

    Donkeyshins

    Posts : 19
    Join date : 2011-07-18

    Re: Another Stereo 70 rebuild

    Post by Donkeyshins on Sun Jan 05, 2014 1:32 am

    tubes4hifi wrote:Donkeyshins,
    hey, since that driver board is above the chassis, you would have room for my new bias test jacks,
    see on the right side of my webpage here:    http://tubes4hifi.com/MK3.htm

    Actually, the board is below decks, so to speak, so I'm not sure I'd have room.  Crying or Very sad

    However, something like that was what I was thinking.

    -D

    Sponsored content

    Re: Another Stereo 70 rebuild

    Post by Sponsored content Today at 4:24 am


      Current date/time is Thu Sep 29, 2016 4:24 am