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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

What should I build with this salvaged radio transformer?

Discussion in 'Shock Brother's DIY Amps' started by Nickfl, Dec 7, 2017 at 2:52 AM.

  1. Nickfl

    Nickfl Tele-Holic

    707
    May 24, 2016
    Florida
    I have a power transformer from an old circa 1940 Zenith console radio that I recently got around to testing. The transformer works and its a nice, heavy chunk of iron so I will want to eventually use it for a build, but I am not sure what it would be best suited for. It has an unloaded HT secondary voltage of 382-0-382, along with 6.3v and 5v heater secondaries. The schematic for the original radio shows a loaded voltage of 325, which sounds about right based on the unloaded reading. I am guessing I would see a B+ of around 395v with a 5y3, 445v with a gz34, and around 455v with a silicone diode. Based on the tube compliment on the original amp the current handling is probably around 150ma.

    So what should this become? I've previously built a 5e3 and amps based on a 6g3 and a supro thunderbolt (as well as a couple of others that this PT wouldn't work for) and I'm not interested in revisiting those. I am also currently working on a modified Princeton reverb (which this actually would have worked pretty well for, but I've already got a PT ordered for it). Outside of that, I am open to suggestions.
     

  2. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    some 2x6L6 beast? Vibrolux Reverb style maybe?
     

  3. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    42
    Mar 1, 2010
    Kent, OH
    Was the original speaker a field coil speaker? If so, your unloaded voltage might be quite high because the field coil speaker would have dropped a fair bit of voltage.
     

  4. Nickfl

    Nickfl Tele-Holic

    707
    May 24, 2016
    Florida
    Yeah it did have a field coil speaker. It was a 2x6v6 amp that probably had less than 300v on the plates of the power tubes, but since I am not rebuilding the original amp or planning anything with that kind of speaker, the higher voltage is what I will have to deal with. Unless I used a choke input power supply, which seems impractical at best, or a BIG resistor or some zeners to drop the voltage.

    That was my initial thought as well. My concern is that the 150ma (probable) current rating might be a bit low for something like a 5f6a since most power transformers sold for similar amps seem to be in the 200+ ma range. I can't seem to find a definitive answer, but my calculations for a 5f6a would be about 80ma at idle, which would still give me less than 150ma at max. I could go cathode biased 6l6, but that seems like it is leading me down the road to something pretty similar to the Thunderbolt.

    I've been thinking about doing an octal preamp 6v6 like a 5c3 and I could use this transformer if I dropped 40 or 50 volts off of the B+ with zeners.
     

  5. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    42
    Mar 1, 2010
    Kent, OH
    With a 382-0-382 PT, I think with a 5U4/5Y3 you will see more like 465V range.
     

  6. Dacious

    Dacious Friend of Leo's

    Mar 16, 2003
    Godzone
    Tweed Tremolux? Mind you that's almost a 5E3. Low power Tweed Twin? 3 X 10 Bandmaster? Maybe with JJ 6V6s pushed a bit?
     

  7. printer2

    printer2 Poster Extraordinaire

    May 24, 2010
    Canada
    Don't worry about the mA rating, it should be fine for a 5F6. So it makes 45W rather than 55W.
     

  8. Nickfl

    Nickfl Tele-Holic

    707
    May 24, 2016
    Florida
    It's 382 totally unloaded, I'm guessing it'll be 10-20% lower under load, which is about in line with the schematic.
     

  9. Nickfl

    Nickfl Tele-Holic

    707
    May 24, 2016
    Florida
    Maybe a tweed pro? Low power twin is deeply tempting... I keep coming back to 5881 tubes.
     

  10. kneedeepinit

    kneedeepinit TDPRI Member

    Age:
    54
    35
    Oct 3, 2017
    calgary
    the simple solution is an amp with two 6V6 as that what what the transofrmers' former life was. If you are looking for a 2nd 5E3, that would be obvious. If you are looking for something different, maybe try something off this page

    http://chasingtone.com/dvnator/category/6v6pp/
     

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