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A friend gave me his burnt out 1957 Gibson GA-5 Les Paul Jr. amp.

Discussion in 'Amp Tech Center' started by EdgeGuy, May 22, 2020.

  1. Nickfl

    Nickfl Friend of Leo's

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    I don't know, you could "roll the dice" on a lot of other seller's tubes for that price... Thats almost $30 shipped for a tube that sells all day long for $5. I've often paid less than that for entire old radios and almost every single one of them came with a USA made 5y3 that was still going strong (to be clear I mean that some of them came with other rectifiers, I've yet to come across a dead 5y3).

    A guarantee from a reliable vendor is definitely worth something, but I don't see the need in the case of old rectifiers, they seem to have been pretty bullet proof and the equipment they came out of usually didn't push them too hard.

    YMMV, its definitely a judgement call and I'm always willing to take a chance on used tubes if the price is good enough.
     
  2. Nickfl

    Nickfl Friend of Leo's

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    What makes you so sure they know what you have? From what I've seen they are big on "trust us, don't worry about the technical data". That and the unreasonable prices have kept me away from them. On the other hand a lot of people on various forums look to them as a gold standard (rightly or not) so they do give you some street cred as a quality restoration in some circles.
     
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  3. tubegeek

    tubegeek Friend of Leo's

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    Mine's bigger.
     
  4. tubegeek

    tubegeek Friend of Leo's

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    I'm sorry - did you say "Edcor"?

    I thought you did. ;D

    (To clarify: Edcor actually does make excellent, properly-spec'ed transformers, they don't just say they do. They'd be a good value proposition even if they weren't cheaper.)
     
  5. Nickfl

    Nickfl Friend of Leo's

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    Edcor also lists the specifications on their website, which unlike Mercury makes it a lot easier to know what you're actually getting. If it wasn't for the fact that their lead times are often 2 + months and their shipping alone can cost as much as a medium sized transformer I'd buy from them as my first choice.
     
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  6. gusfinley

    gusfinley Tele-Afflicted

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    You may never find the exact transformer you are looking for!

    Another challenge is finding a transformer with the wires exiting only one end bell.

    Here are a few good fits electrically:

    http://www.classictone.net/40-18085.pdf

    https://edcorusa.com/xpwr014

    These could be close electrically and mechanically, but have wires exiting each end bell.

    https://www.hammfg.com/files/parts/pdf/271X.pdf

    https://www.hammfg.com/files/parts/pdf/272BX.pdf

    https://www.hammfg.com/files/parts/pdf/272X.pdf


    If you're really bent on getting it just right, try contacting Heyboer or Edcor. I have contacted Heyboer about transformers in the past and they have found designs in their files and quoted me reasonable prices.
     
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  7. tubegeek

    tubegeek Friend of Leo's

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    Shipping isn't cheap, but let me tell you there's nothing like the feeling of opening up a box with four or five of those blue beauties snuggled in there. (A buddy and I bought outputs for two stereo compressors, so, four in total.) There would be good reason to do a group Shock Bros buy from Edcor if there was a bunch of interest in a big batch of similar items, come to think of it....
     
  8. EdgeGuy

    EdgeGuy Tele-Meister

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    I'm still in conversation with MM. They were confused by the footing of my transformer so I sent them a pic. They responded with "Interesting. You have a variation which is not surprising with vintage Gibson amps.". They then offered to rewind it so I sent them the pics of what it looks like on the inside to see if the offer still holds. It's pricy for them to rewind it if they could.
     
  9. tubegeek

    tubegeek Friend of Leo's

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    Sounds like progress, at least.
     
  10. EdgeGuy

    EdgeGuy Tele-Meister

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    I was given an amp made during a transition between the Les Paul Jr. and the Skylark. It has a Skylark circuit but not a Skylark transformer and then they tossed it in a remaining Les Paul Jr. chassis. Maybe I should get MM to rewind this. It's kind of unique. Then again, maybe there's a reason why this transformer looks the way it does today and MM could just be rewinding an early bad decision from Gibson.
     
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  11. tubegeek

    tubegeek Friend of Leo's

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    Yeah, I'm not really convinced getting a duplicate of the installed transformer is the best way to go, when you can get (already got, right? the Stancor?) something that will reliably work well. If you're worried about drilling holes/originality, attach a bracket. If you're worried about the missing ground wire (which perhaps attaches to an isolating shield/perhaps just attaches to the core) I'd say it is worth a shot trying without it.
     
  12. gusfinley

    gusfinley Tele-Afflicted

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    How much do you feel the amp is worth in its current condition? It seems that you have stated that the amp's value to you is purely sentimental. If you want to keep it original that would be doing what is best for your pocket to maintain its value.

    Since it seems like this chassis may have been meant for a different transformer, have you considered doing what is best for the amplifier? If you want decades of reliable operation, you couldn't go wrong with a Fender Champ style transformer.
     
  13. EdgeGuy

    EdgeGuy Tele-Meister

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    The issue with the Stancor is the 40ma. I wish I had found the OxyClean before I ordered it. MM says I have an oddball transformer but that my circuit needs 70ma. I was warned about that.
     
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  14. tubegeek

    tubegeek Friend of Leo's

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    Sorry - I overlooked that part. Agree on holding out for a 70mA. Make a preamp or something out of the Stancor.
     
  15. EdgeGuy

    EdgeGuy Tele-Meister

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    I have considered doing that but my first choice (which I haven't exhausted yet) is to find a drop in replacement. My transformer has a Faraday shield between the primary and secondary that takes RFI to ground rather than giving it to the secondary. None of the Champ style transformers have that but MM remade the Skylark transformer with this ground and 70ma. I don't know how effective this shield is but if I don't get it, then I never will. MM re-makes the normal Skylark transformer although it's slightly bigger than mine. My transformer was clearly the earliest Skylark. I still haven't heard back from MM to see if re-wiring my transformer is even an option. I sent them pics of how burnt out it is. All the paper in the transformer is now carbon and the wire might even be fused. I know nothing about the subject.
     
  16. gusfinley

    gusfinley Tele-Afflicted

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    It sounds like the MM transformer may be what is best for the amplifier if it is a drop in fit. Perhaps if you request a mechanical drawing of the transformer you can verify this before purchasing. I would also verify that the the leads only exit from one end bell before purchase.
     
  17. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Transformers are fairly simple devices. Just coils of wire with metal plates to make the metal core for the coils. The paper is used for insulation. The only parts reused in a rewind is the metal plates and the frame/end bells. All of the wire would be replaced.

    If the specs of the PT were unknown the diameter of the wire, the thickness of the enamel, and the number of turns would need to be determined to make a clone.

    The PT could be modded by using slightly thicker diameter wire to increase the mA rating of the winds. Different number of turns can be used to change the voltages up or down.

    (Of course the size of the PT would limit wire size and number of winds. Extra plates can be added to allow for changes by increasing the physical size of the PT.)
     
  18. EdgeGuy

    EdgeGuy Tele-Meister

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    I could have MM re-wind the transformer for $280. I'll just get their Skylark transformer. It's what Gibson eventually settled on for my circuit while my transformer was an early fail.
     
  19. EdgeGuy

    EdgeGuy Tele-Meister

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    The transformer won't fit so I will have to use standoffs. I have to think that my transformer may not exist. It could have been a test one that Gibson wasn't happy with. I'll save the old transformer for the next owner after I die.
     
  20. gusfinley

    gusfinley Tele-Afflicted

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    What do you mean by "use Standoffs"

    Here are some odd ways that I have mounted transformers:

    http://enginerdamps.blogspot.com/2008/03/non-standard-transformer-mounting.html
     
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