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Really old NOS output transformers, use them or put them in trophy case?

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  • Really old NOS output transformers, use them or put them in trophy case?

    I managed to find a couple of NOS Hammond transformers, a 57 and a 68. According to a Hammond catalog the specs are as follows:

    Hammond 57, Single tube, 7000 primary impedance, tubes (6F6, 42, 6K6, 7B5), secondary impedance 3.2, core size 1/2x1/2, wgt 3/8, code Ephar
    Hammond 68, Push-pull, 14000ct primary impedance, tubes (6F6, 42, 6K6, 7B5), secondary impedance 3.2, core size 5/8x5/8, wgt 1/2, code Ekart

    Never having built a tube amp before, I interpret this as meaning I could build something like a 6V6 single ended with the Hammond 57 or a 6V6 push-pull with the Hammond 68. Or build something with really cool looking octal tubes.

    My question is should I build with them or just display them? I mean it probably won't be too long before these are a century old and maybe they deserve to be preserved as-is since they survived this long in their funky little boxes. Or is it a bad idea to use such old iron, NOS or not?

  • #2
    Use them! 6v6, just as you said. Photos, pls!
    --
    I build and repair guitar amps
    http://amps.monkeymatic.com

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    • #3
      That Hammond 68 has a really high primary impedance. Typical 6v6 push pull circuits for guitar amps are 8K or 6.6K. Also, you're not going to be able to find a "3;2" ohm speaker, so the 4 ohm speaker you'll use will reflect an even higher impedance on the primary. It'll work, but power output will be well down. I'd sell these to people who have drunk the "vintage" cool aid and use the money to buy modern transformers that have the specs you need. The hammond 57 seems more in the realm of reasonableness, that'll work for a fender champ type single ended circuit with a 6v6.

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      • #4
        Originally posted by octal View Post
        That Hammond 68 has a really high primary impedance. Typical 6v6 push pull circuits for guitar amps are 8K or 6.6K. Also, you're not going to be able to find a "3;2" ohm speaker, so the 4 ohm speaker you'll use will reflect an even higher impedance on the primary.
        A 2 ohm load would lower the primary impedance. But that would mean using two 4 ohm speakers, which might be overkill for a single 6V6 amp.

        Originally posted by Enzo
        I have a sign in my shop that says, "Never think up reasons not to check something."


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        • #5
          They are meant for old tube radios. Get in to that hobby while you have a head start.

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          • #6
            I think those would be small even for a single 6V6. The high impedance of the 68 not withstanding. I agree with octal and/or mozz. Sell them to true believers and buy something more useful for our genre or get into vintage tube radios. Whichever appeals to you. But DON'T put them in a shadow box on display and take them out of circulation forever. They're not as collectible as they are useful in the right application.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "If you're not interested in opinions and the experience of others, why even start a thread?
            You can't just expect consent." Helmholtz

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            • #7
              Forget collectors, kids donīt care about old stuff, even less tube, old farts like us wonīt stay around much longer.
              E Bay them and get some money, remark Mojo, 100 y.o., pixie dust (besides actual collected grime), etc. , somebody might pay what they are not worth.
              Agree they are cheesy old tube table radio stuff.
              Juan Manuel Fahey

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              • #8
                I'll see if I can trade these for something more useful when the world returns to normal and we have group meetings again. There is a vintage radio club that used to meet a couple times a year not too far away from me. A few years ago I picked up a nice Bogen 6V6 PA amp there. Thanks for setting me straight on these.

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                • #9
                  Necro my own post because I forgot to post pictures I took at the time... Click image for larger version

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