1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

OT Transformer, and rectifier tube questions

Discussion in 'Shock Brother's DIY Amps' started by Jewellworks, Jul 20, 2020.

  1. Jewellworks

    Jewellworks Tele-Meister

    Posts:
    357
    Joined:
    Mar 2, 2020
    Location:
    Orlando
    my next conversion build has an unknown OT Transformer (Halldorson) with what looks like 3 taps. how do i figure out whats what? my guess is 4ohm, 8 and 16 ohm, but thats only a guess.

    it also comes with a 5V4 rectifier. any opinions? Uncle Doug likes the GZ34 with its slow start up time (s'posed to be easier on the rest of the tubes), but ive also read that the 5V4 is a lot more "steady" with inconsistent supply voltages, which is a big help in central Florida...
    opinions?

    also, are there adapter sockets for the larger octals to plug a 12ax7 in its place? or do i have to cap and drill a new hole for the 12AX7?
     
  2. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    I have seen "hole shrinker" plates that will let you mount a 9-pin in the hole left by removing an octal.

    I think bottlehead.com used to sell them?
     
  3. jtcnj

    jtcnj Tele-Holic

    Age:
    57
    Posts:
    599
    Joined:
    Feb 2, 2015
    Location:
    N.J. USA
  4. andrewRneumann

    andrewRneumann Tele-Holic

    Posts:
    593
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    Do you own a variac? You could use that and a multimeter with a small AC voltage to determine the turns ratio for each tap. I would be tempted to use 120VAC on the primary winding of an OT, but I’ve never tried it so consider that a hair-brained idea that only a fool would consider.
     
  5. schmee

    schmee Doctor of Teleocity

    Posts:
    14,967
    Joined:
    Jun 2, 2003
    Location:
    northwest
    -The 5V4 is a good rectifier, just keep it. They are cheap and plentiful. I use them occasionally in place of the hard to find 5AR4. I think I have one in one of my vintage Deluxe's right now. There are also a few 5V4's out there that are actually 5AR4's rebranded. When you find one it's a great bargain!
    -I think Weber sell the plates to fill a hole converting to a 9 pin tube. They used to.
    -There must be adaptors out there.
     
  6. David Barnett

    David Barnett Doctor of Teleocity

    Age:
    64
    Posts:
    14,769
    Joined:
    Mar 17, 2003
    Location:
    The Far-Flung Isles of Langerhans
  7. David Barnett

    David Barnett Doctor of Teleocity

    Age:
    64
    Posts:
    14,769
    Joined:
    Mar 17, 2003
    Location:
    The Far-Flung Isles of Langerhans
    jtcnj and tubegeek like this.
  8. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    Much simpler to find a wall adapter with an AC output, 6 or 9 or 12 or whatever. Then do the ratio of input voltage to output voltage.

    To find the impedance ratio square the ratio you just measured, i.e., if the voltage ratio you just measured was 25:1 then the impedance would be 625:1. An 8 ohm load would show a 5K load to the tube.
     
    D'tar, andrewRneumann and Kevin Wolfe like this.
  9. elpico

    elpico Tele-Afflicted

    Posts:
    1,190
    Joined:
    Sep 14, 2011
    Location:
    Vancouver BC
    Is there some external reason to buy an octal to 9 pin adapter, like you own a collection of nos 12ax7 that you want to use? If not there's no need to buy that. Octals sound really good. The 9 pin miniature versions of them were just made to save space, not because they sound better.
     
    D'tar and tubegeek like this.
  10. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,483
    Joined:
    Dec 30, 2019
    Location:
    california
    You can find the winding ratio with a variac or other AC device. What are we talking about here? Push Pull or Single ended? (You may be able to decipher with resistances if we can find an existing OT with a close match.)
    You do not want the octal 6SL7 family of tubes taking up space?
     
    tubegeek likes this.
  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,483
    Joined:
    Dec 30, 2019
    Location:
    california
    I see a Halldorson catalog after a search. If you have any numbers it may help.
    Stancor catalogs are available as well.
     
  12. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    Note that I will gladly provide storage for them.
     
  13. RollingBender

    RollingBender Tele-Afflicted

    Posts:
    1,496
    Joined:
    May 14, 2011
    Location:
    SW Minnesota
    Just make your own adapters. All it takes it a bit of 1/8” aluminum plate and a CNC machine.
    8508998D-C28C-4BA3-95D0-FD67F9C89CD8.jpeg
    686F5CCE-7A17-4815-A141-DF3C06FF943A.jpeg
     
  14. Jewellworks

    Jewellworks Tele-Meister

    Posts:
    357
    Joined:
    Mar 2, 2020
    Location:
    Orlando
    Push Pull

    I've read they only have a factor of around 35. 12AX7 s are 100. More is more, right? Especially if i plan on building a JCM800 6V6

    I may just drill them out and put in 12AX7 plates
     
  15. Jewellworks

    Jewellworks Tele-Meister

    Posts:
    357
    Joined:
    Mar 2, 2020
    Location:
    Orlando
    Don't have any of that, but I'll take 5 if your selling...
     
  16. Jewellworks

    Jewellworks Tele-Meister

    Posts:
    357
    Joined:
    Mar 2, 2020
    Location:
    Orlando
    The chassis shows a 5V4 should go there. What's actually plugged into that socket is a 5U4.
    Any difference?
    Obviously, I need to o look at the data sheets for all these tubes
     
  17. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY

    You've read wrong.

    6SL7: mu of 70
    6SN7: mu of 20
    (12AX7: mu of 100)

    In each case mu is the maximum possible gain theoretically available from the tube, in a practical circuit, actual gains are always less than mu. To get the gain equal to mu you need an infinite power supply voltage together with an infinite plate resistance. Alternatively, an inductor with an infinite inductance and 0 DC resistance. Both options are somewhat difficult to obtain in practice.
     
    Nickfl likes this.
  18. Jewellworks

    Jewellworks Tele-Meister

    Posts:
    357
    Joined:
    Mar 2, 2020
    Location:
    Orlando
    i have a 6SJ7 in V1. ive got a 6V7 in V2 & V3 (PI), and a pair of old big bottle 6L6's, and a 5U4 rectifier
     
  19. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    3,483
    Joined:
    Dec 30, 2019
    Location:
    california
    The 5U4 drops more voltage.
    The 5U4 is rated 3A current vs 2A for the 5V4.
    The 6SJ7 is a pentode. IDK the mu. *Usually* pentodes provide more than 100mu from My recollection.

    I would want to hear the pentode in action. Some good tone can be in that box.
     
  20. schmee

    schmee Doctor of Teleocity

    Posts:
    14,967
    Joined:
    Jun 2, 2003
    Location:
    northwest
    Yes, the 5U4 draws a lot more amperage. I'd change back unless you know the PT can handle it.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.