The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


    Dynaco ST-70 Series 3

    avatar
    Spoon

    Posts : 2
    Join date : 2020-09-29

    Dynaco ST-70 Series 3 Empty Dynaco ST-70 Series 3

    Post by Spoon on Wed Sep 30, 2020 8:38 pm

    I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
    Dave_in_Va
    Dave_in_Va

    Posts : 380
    Join date : 2013-04-02

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by Dave_in_Va on Thu Oct 01, 2020 12:00 am

    I'm not familiar with your amp but I have a VTA ST 70 and tried Gold Lion KT 88's. The inexpensive Valve Art EL 34's that came with the amp sounded better.
    (I eventually settled on NOS Mullard EL 34's).)

    Spoon likes this post

    peterh
    peterh

    Posts : 1434
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by peterh on Thu Oct 01, 2020 4:09 am

    Spoon wrote:I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.
    As the critical grid resistor in ser III is 275k it's on the limit for KT77. There is
    a risk for current avalanche aka redplating if luck goes out.
    https://frank.pocnet.net/sheets/084/k/KT77_GEC.pdf
    KT88 on the other hand is well within limits:
    https://frank.pocnet.net/sheets/084/k/KT88_GEC.pdf

    As for filament current, KT77 draws 1.4A EL34 1.5 and KT88 1.6A
    KT88 will then load the powertransformer with 400mA extra or 2.5w.
    This seems like a small amount.

    Dave_in_Va and Spoon like this post

    avatar
    rjpjnk

    Posts : 264
    Join date : 2018-07-18

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by rjpjnk on Sun Oct 04, 2020 12:15 am

    Spoon wrote:I have a Dynaco ST70 Series 3. I’d like try out Gold Lion KT77 or KT88 output tubes. Can anyone confirm that it’s safe to do so? The stock tubes are JJ EL34/6CA7.

    I have the Series 3 as well and I think the OEM JJ E34L tubes sound great, but then I have only tried one other set so far for comparison, the Mullard reissue EL34. Are you looking for more power or just a different sound?
    avatar
    Spoon

    Posts : 2
    Join date : 2020-09-29

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by Spoon on Sun Oct 04, 2020 10:41 am

    Just sound difference. I've read great things about the GL's.
    avatar
    rjpjnk

    Posts : 264
    Join date : 2018-07-18

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by rjpjnk on Sun Oct 04, 2020 1:16 pm

    Please report back with your impressions if you try them. Thanks!

    Spoon likes this post


    Sponsored content

    Dynaco ST-70 Series 3 Empty Re: Dynaco ST-70 Series 3

    Post by Sponsored content


      Current date/time is Wed Oct 21, 2020 11:32 pm