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


    Hello im a new Forum person.

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    zipper

    Posts : 6
    Join date : 2015-06-15
    Age : 48
    Location : Porcupine Ontario Canada

    Hello im a new Forum person.

    Post by zipper on Mon Jun 15, 2015 3:54 pm

    Hello im a new Dynaco Tube Audio Forum person. Thank You Bob Latino, your site and many many compelling replies to endless questions convinced me to buy within the last 6 month a Dynakit ST70 and then a pair of MKIII's.

    I am new with no idea what to do on Tube amplifiers. I know how to use my meter and I know the differences in caps and resistors and how to read them. So I think I can make my way through keeping my new Dynaco/Dynakit amps running.

    The stock ST70 was loved and looked after and arrived fully functional. Only necessary changes were made before I got it. I was looking for stock and un-moded units. It is being used as we speak on some vintage Cornwalls.
    The MK III's are pretty much stock also but the SDS Labs capacitor board mod was installed into one of the amps. I will install the other shortly. (units are shelved until all necessary updates are done i.e.. not running) These also has some pretty grimed up Driver boards..

    I have ordered the Diodes for the Selenium Rectifier replacment.
    Any suggestions on what else I should do immediately on the MK III's. I only want to change what I need to to stop it from blowing up in the short term. Caps .. resistors?

    Probably a dumb question but if I have the SDS cap boards installed in the MK III's Im guessing I do NOT need to upgrade the 30/20/20/20 uF Capacitor Can.?

    Last question for today... Can I drop in KT88's into the stock Dynakit ST70 and simply re-bias or do i need to do a few other things under the hood to make this happen.

    I will add pics ASAP as soon as my probation week is up.

    I looked for the RULES area and could not find it.. I hope I have kept to the guidelines of this Forum.

    Thanks everyone

    Chris

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: Hello im a new Forum person.

    Post by stewdan on Mon Jun 15, 2015 7:55 pm

    Hi Chris --- Welcome to the Forum!!

    Yes, the SDS Cap Board on the MK3 amp (and also on the ST70 amp) "replaces" the 4-section Quad Cap. (each pair of caps on the PCB replace 1 section of the Quad Cap .... 8 caps total replace the 4-sections of the quad.)

    What most of us have done is leave the Quad Cap where it is, but electrically disconnected underneath the chassis and then wire the SDS Board appropriately. Then we don't have a see-thru hole visible in the chassis.

    The www.tubes4hifi.com website has downloadable build manuals for the original Dynaco tube amps. Tuners and Preamps along with the stock schematics and voltage test points and values. Take a look if you need the manuals.

    Have fun,
    Stew


    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Hello im a new Forum person.

    Post by tubes4hifi on Tue Jun 16, 2015 6:53 pm

    a 50 year old stock Dynaco ST70 is NOT up to the task of powering 4 KT88 output tubes without overheating the power transformer.
    (KT88 filaments are 2 amps each, compared to EL34s at 1.5 amps each, so that's a 33% increase)
    You can replace the old power transformer with a new one which are rated higher, but they run about $140.

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