Dynaco ST-35 Build – DG Style

Discussion in 'Tube Audio' started by njcanuck, Jan 28, 2017.

  1. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    I’ve heard so many great things about the little Dynaco ST-35 that I have to have one. Since used ones are hard to find and don’t support 4 Ω taps, I’ve decided to build from scratch. Thought I would start a thread on the subject as there always seems to be interest in these little amplifiers. So follow along and pitch in to offer improvements (or if you see me screwing up).

    When complete, it will drive Altec Segovias (4Ω) or Klipsch Chorus (8Ω).

    Parts are currently on order as follows:

    - Boards from our own Dave Gillespie. This includes two PC-13 output boards and his famous EFB power supply board. Hence the ‘DG Style’ in the title. (I’m also counting on him to bail me out if I run into trouble:rolleyes:).

    - Components from Mouser to populate the boards. They had everything in stock.

    - Transformers, chassis and tube sockets from Dynakit Parts. Beefier PT than original and outputs with 4 ohm and 8 ohm taps. The chassis is stainless steel.

    - NOS Mullard 7247 tubes from AK’s B. Youngman vault and 6BQ5s or 7189s from my own stash (I’ll see how they match up).

    Now I wait for enough parts to arrive to start the build. :boring:
     
    malden, invaderzim, derekva and 2 others like this.

     

    Please register to disable this ad.

  2. Lavane

    Lavane AK Subscriber Subscriber

    Messages:
    7,718
    Location:
    northern cal.
    :lurk: Ill be watching this thread closely. I had the same thought. Right down to the chassis and iron.
     
    invaderzim likes this.
  3. derekva

    derekva This ain't no picnic... Subscriber

    Messages:
    4,853
    Location:
    Woodinville, WA
    Also interested. I've done a P2P Gillespie Stereo 35 which is perhaps my all-time favorite amp (sounds fabulous with my custom Heresy IIIs). Although apparently I need to ping BYoungman for some Mullard 7247 tubes!

    -D
     
  4. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    He says he has more. :thumbsup:
     
  5. peterh

    peterh AK Subscriber Subscriber

    Messages:
    1,920
    Location:
    Gothenburg,Sweden
    Picture man, pictures !
     
  6. Lavane

    Lavane AK Subscriber Subscriber

    Messages:
    7,718
    Location:
    northern cal.
    What about Triode's so called ST35? Is it a ST35 all on one board, or a new animal, anyone know?
     

     

    Please register to disable this ad.

  7. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    I did see Triode's all-in-one board and it looks pretty interesting. It also replaces the 7247s with a 12AX7/12AU7 combination. However, I really wanted to employ Dave's EFB circuit which is really easy to do with his board. Having previously used EFB on a Fisher amp, I wouldn't consider any other direction!

    FWIW Triode's transformers are considerably more expensive than Dynakit's but reportedly measure the same.
     
    Lavane likes this.
  8. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    Woohoo! First delivery - the mailman just delivered Dave's boards. They are sweeeeet!

    I also managed to snag six Raytheon 6BQ5s, branded Baldwin, that all test close to NOS. I'm betting that they're closely current matched as well. :thumbsup:

    Dyna 01.jpg Dyna 02.jpg
     
    derekva likes this.
  9. StuartB

    StuartB AK Subscriber Subscriber

    Messages:
    1,059
    Location:
    Ohio
    Good luck. I am just starting to rebuild a SCA-35 with Dave's boards. Have the cards and components in hand. Had to use Mouser, DigiKey and Tube Depot to get everything I needed.
     
  10. nj pheonix

    nj pheonix AK Subscriber Subscriber

    Messages:
    10,149
    Location:
    New Jersey
    Rich,
    There's an old expression that the way to judge another man's intelligence is to see how much he agrees with you. Your project is one i've had in the back of my head for some time (though i likely never was going to get to it:biggrin:).
    I will be watching this one:lurk:
    Hey, we're missing you here in NJ
     
    Dandy likes this.
  11. Shadowdog

    Shadowdog Super Member

    Messages:
    2,903
    Location:
    Flin Flon, Manitoba
    Nice amps! Looked at Triode's transformer bundle and if you take out the included choke (for diytube version) it's only $18 more, but
    they are the originators of exact replacement ST-35 OPT trans.
     

     

    Please register to disable this ad.

  12. derekva

    derekva This ain't no picnic... Subscriber

    Messages:
    4,853
    Location:
    Woodinville, WA
    What are you using for a chassis? Are you going with the reproduction Stereo 35 chassis from Dynakit Parts or are you doing a custom chassis with a bit more real-estate?

    -D
     
  13. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    Missing you guys, too, but not the snow and cold. :no: I have my coffee outside almost every morning, now. :thumbsup:

    Also missing the Kutztown antique radio shows - I picked up a lot of good stuff there! Haven't found anything like it here.
     
  14. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    I'm going with the Dynakit repro. I did consider a larger, custom chassis for extra space; even considered going point-to-point but in the end decided to stick with the original small form factor. It will be fine for my purposes. The only extra real estate that I might need would be for a small individual-bias board and I'm pretty sure I can squeeze that in. I might not even need it - it will depend on how well matched my tubes are.
     
    derekva likes this.
  15. chopchip

    chopchip New Member

    Messages:
    1
    SAM_0974.JPG
    i have had one of those for a long time. it sounds good to me but i never heard an original dynaco one to compare it to. it likes to eat rectified tubes but a mod with a diode fixes that. i dont use a rectifier tube on it instead i use one of those SS rectifiers and i power it up slowly with a variac or a Thermistor can do the job too to protect the circuit from a hard start.
     

    Attached Files:

  16. derekva

    derekva This ain't no picnic... Subscriber

    Messages:
    4,853
    Location:
    Woodinville, WA
    What you have there is a Stereo 70, which uses EL34 tubes.

    The Dynaco Stereo 35 uses EL84 tubes:

    [​IMG]

    Or more accurately, what the OP's amp will probably look like since he's using Dave's boards:

    [​IMG]

    :)

    -D
     

     

    Please register to disable this ad.

  17. derekva

    derekva This ain't no picnic... Subscriber

    Messages:
    4,853
    Location:
    Woodinville, WA
    Yup. Sent him a check for a pair of Hammond badged Mullards on Monday. :)

    -D
     
  18. njcanuck

    njcanuck aka: MacGyver Subscriber

    Messages:
    2,786
    Location:
    Cape Coral, Florida
    Woohoo! Mouser box arrived late yesterday. Time to start populating the boards.

    It has been a while since I've worked on PCBs. On the upside, I'd forgotten how quick and easy it is. On the downside, I feel like I'm not really paying attention to what each component does in the circuit.

    Got the power board finished last night, working on the driver boards now.

    Dyna 03.jpg Dyna 04.jpg
     
    derekva likes this.
  19. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    37,336
    Location:
    Southern NJ
    My 7247's are also Hammond branded. Got them cheap on the used market.

    The ST-35 is surprisingly small once you actually see one. Its smaller than a Magnavox console amp.
     
    derekva likes this.
  20. derekva

    derekva This ain't no picnic... Subscriber

    Messages:
    4,853
    Location:
    Woodinville, WA
    Yep. Slightly larger than a Fisher 30A (which is a MONO amp).

    -D
     

Share This Page