Are these transformers worth bothering with?

Discussion in 'Shock Brother's DIY Amps' started by dfrosto, Nov 4, 2019.

  1. dfrosto

    dfrosto TDPRI Member

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    I unearthed some transformers in some equipment I had gathering dust. There is a power and output transformer from a '60s tube mono reel to reel tape deck, and also one from a FM tuner. I like the idea of repurposing them, assuming they work, but have no idea if they would be useful in a Micro Champ, for instance, or another low watt guitar amp. The tape deck has 4 tubes:
    6AQ5A
    12AU7
    12AX7A and
    6ME5 "Magic Eye"
    I don't know if that's meaningful information, but am curious if anyone has ideas about utilizing any of this stuff for a fun build. I don't have any amp building experience at this point, so the point may be moot!
    Here's some pics. The first is from the tuner, the other 2 are from the tape deck. Thanks for looking! 1031191528.jpg 1013191820.jpg 1104191044.jpg
     
  2. schmee

    schmee Poster Extraordinaire

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    I dont see why not in the right application.
     
  3. dfrosto

    dfrosto TDPRI Member

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    Thanks- I guess where I was going was to try get some insight into what the numbers are telling me.
    40 ma? does that cut it? I've seen 70 - 100 ma mentioned. Is 40 useless, or just underpowered?
    250 volts? Is that enough?
    Trying to learn this foreign language!
    I see some really inexpensive power and output amps out there. How much "juice" do you need to get a less than one watt amp working? If I can use these components, great! If not, I can get over it. Just askin'!
    .
     
  4. Dacious

    Dacious Poster Extraordinaire

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    Middle one is a tube heater with 1 amp and 0.4 amp windings to run a power tube and a separate preamp,would be fine in something like a Vox AC4 or Dano/airline amp, single preamp single power tube.

    Top one110/115/250 is the primary with 6.3 being secondary.

    215v through a ss rectifier will give you 300+. Lots of small SE amps are right around there.

    The 6k 4 ohms would work for a pair of 6AQ5 tubes to something like a Champ speaker - 6AQ5 is the mini 7-pin version of a 6V6. I had a converted PA head with 6V6s (half a 12AX7) and 6AQ5 in push-pull. It was a little screamer.

    You could make a mini Tweed Deluxe with them.
     
    Last edited: Nov 4, 2019
  5. Corvus

    Corvus TDPRI Member

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    I've made a number of Champ/Princeton type amps using a 250v output transformer but I'd say 40ma is low and would run hot if pushed. I think you need to look at a single output tube and the 6AQ5 is a good bet. El 84 also runs well of this voltage.
     
  6. BruceF

    BruceF Tele-Meister

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    I have built a couple of Rob's micro deluxe amps with a power transformer 500 v ct and 40ma using solid state rectifiers with no problems. Two little tubes don't draw much.

    From Rob's web page on the micro deluxe: "The amp pulls a total of 17 milliamps of B+ current using a 12AU7 power tube"
     
  7. gusfinley

    gusfinley Tele-Holic

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    I'm not sure I can read all of the taps on the transformer in the first picture. I think I see a 160 CT secondary but also a 210V? Maybe the 210 is the primary and not the secondary.

    You best bet is to add up all the current requirements of all of the tube that the transformer was powering. This will give you an idea of how much juice it can provide.

    I used a very similar looking transformer in a few builds, and all the currents added up to be able to power a 15Wish amp. I built a Marshall 2061x clone, but found it wasn't for me. I eventually put in one of my cheap champ builds and eventually sold the transformer in a champ-style build (no cab/speaker) for $90 on a local online classifieds.
     
  8. printer2

    printer2 Poster Extraordinaire

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    The output transformer is single ended and works with the 6AQ5, almost a no brainer. The power transformer puts out enough for the 6AQ5 and a couple of preamp tubes, sounds good to me. A 12AX7A and 12AU7, a number of options available, even two 12AX7's. Let's say you have a 2-3W amp there. The preamp could be Champ inspired, could have tremolo. Or a Marshall flavored sound with three stages of gain and a cathode follower.
     
    muchxs likes this.
  9. muchxs

    muchxs Doctor of Teleocity

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    Yup.

    Those are Japanese "export" transformers. Eyeball and diagram them carefully before removing them. They have a few Japanese export quirks. For example they have 100v (Japan) and 115v (U.S.) primaries. They're both set up for solid state rectifiers.

    If you copy and emulate the existing rectifier circuit they're both useful. One will make a dandy little 6AQ5 amp 'cuz that's what it runs already. The 40ma thing will make a nice "flea" amp using a reverb driver for an audio output.


    I scored a couple similar transformers at the recent NEARfest at the Deerfield (New Hampshire) fairgrounds. The bigger one ran a tube stereo with four 6BM8 tubes and a 5AR4 rectifier. Plate voltage is around 250v.
     
  10. dfrosto

    dfrosto TDPRI Member

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    Thanks for all the responses, sounds more promising than I thought! I'd like to incorporate them into a Micro Champ build, if I can do it by simple substitution without getting in over my head. My concern was that one change might lead to another, and another... I'm not ready to design or redesign an amp!
    Do you think I could just slide them into the Micro Champ circuit, and leave the rest the same? That's kinda what I'm hoping!
     
  11. printer2

    printer2 Poster Extraordinaire

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    As much said, as long as you copy the power supply that is in the deck there should be no problem. The transformer says 4 ohm and 6k ohm on it, it would like to see a 4 ohm speaker on it. But even with an 8 ohm it should work. Check the value of the cathode resistor on the 6AQ5 in the deck. This would be a good place to start biasing up the tube. The rest of the amp's circuit values are optional.
     
  12. muchxs

    muchxs Doctor of Teleocity

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    It's a good intro to cut 'n' splice circuit design. I often forget that while things like this are second nature to folks like me 'n' @printer2 , "paint by numbers" is often better suited to your first try.

    You're going to need a low buck reverb driver transformer for an audio output in a Micro.

    The 6AQ5 amp has almost everything you need, tubes, transformers, sockets and such if they aren't junk.

    PM me with your location. Maybe we can de- construct you salvage and make some sense of it.
     
  13. dfrosto

    dfrosto TDPRI Member

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    muchxs- started a conversation, not familiar with this forum, is that the way its done?
     
  14. printer2

    printer2 Poster Extraordinaire

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    Much, unless I am wrong I think the output transformer in the third picture goes with the second picture power transformer.
     
  15. dfrosto

    dfrosto TDPRI Member

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    Yes, that's correct- they are both from the little tape deck.
     
  16. muchxs

    muchxs Doctor of Teleocity

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    Yup.

    You know what else is cool? It's marked 6k into 4 ohms right on top.

    I used to scrounge output transformers like that from black and white TVs. There was a time a black and white TVs lit just about every American (Canadians are Americans, too) there was a time when black and white TVs lit every house with that eerie glow.

    Most of those TVs went to the dump.
     
  17. printer2

    printer2 Poster Extraordinaire

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    Do you have the make and model number of the deck?
     
  18. dfrosto

    dfrosto TDPRI Member

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    Printer2, yes the deck is a Lafayette RK-142, early '60s. I looked around for a schematic, couldn't locate one for free and wasn't sure it was worth $12 or whatever to buy one.
     
  19. dfrosto

    dfrosto TDPRI Member

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    Here'a pic of the deck in all its glory. The jack at the top are speaker out, and radio and microphone inputs. 1001191604#3.jpg
     
  20. printer2

    printer2 Poster Extraordinaire

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    Oh well, was hoping to look up a schematic, nice to see what it come out of though.
     
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