Voltages Too High Everywhere on a Super Reverb

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by guitarcapo, Feb 7, 2012.

  1. guitarcapo

    guitarcapo Senior Member

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    I have a blackface reissue Super Reverb that was rewired PTP by a tech after I had trouble diagnosing a problem. He stated that the problem was that a shorted rectifier tube took out a filter cap. While he had it I had him rebuild the amp.

    It has this brittle sound with some angry hum and the voltages are too high everywhere.

    Anyway I'm thinking the problem all along might actually be the power transformer. The voltage after the rectifier (pin 8)is 506V instead of 465V. I can't even READ the voltage coming off the power transformer secondary (should be around 360v) itself because it's too high for my meter which can't read higher than the low 500's.

    My question is, could anything else be the reason for me getting such high readings after the rectifier? I tried a 5Y3 and the voltage only came down to 495V, I don't have another GZ34 to try.

    I'm thinking the PT might need to be replaced but figured I'd ask before spending $100
     
    Last edited: Feb 8, 2012
  2. TweeDLX

    TweeDLX Member

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    That sounds like your answer right there. If it were me, I'd be ordering another PT.
     
  3. davemccarthy707

    davemccarthy707 Member

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  4. Blue Strat

    Blue Strat Member

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    Before doing anything replace the battery in your meter and try again.
     
  5. mageerc

    mageerc Member

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    +1 A weak battery in a DMM can cause all sorts of strange readings...
     
  6. '58Bassman

    '58Bassman Member

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    Check your line voltage. If it's below 120VAC, it would seem that your power transformer has a problem, possibly caused by the rectifier going away. If it's higher than 120VAC, you may have a problem with the neutral in your house.

    Pull your tubes and check your PT primary and secondary voltages, then add the rectifier, re-checking all of the voltages. If the secondary voltages are OK, you might want to try another rectifier, preferably an old one, or one that is known to drop the voltage under load.
     
  7. guitarcapo

    guitarcapo Senior Member

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    I'll do these suggestions tonight and report what I find.
     
  8. Ronsonic

    Ronsonic Member

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    This isn't a technical problem it is a customer service issue.
     
  9. Prairie Dawg

    Prairie Dawg Member

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    Agreed.
     
  10. phsyconoodler

    phsyconoodler Member

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    Quote:"I have a blackface reissue Super Reverb that was rewired PTP by a tech after I had trouble diagnosing a problem. He stated that the problem was that a shorted rectifier tube took out a filter cap. While he had it I had him rebuild the amp."

    Well,to start with,get a new meter.I have never heard of a meter that won't measure under 'the low 500's'.What is that all about?

    It is very likely your meter is lying to you.
    the brittle sounds are something else.Without reliable test equipment you cannot diagnose anything.
     
  11. Jerry Glass

    Jerry Glass Member

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    For what it's worth...that reissue should have around 435vdc to 440vdc at he plates with the power tube biased around 32 to 33mA with a GZ34/5AR4 rectifier.
     
  12. phsyconoodler

    phsyconoodler Member

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    Every reissue I have worked on has 460-470v.I am a Fender warranty tech and see lots of them.I bias closer to 35-40ma.they are dull at 32ma.
    you can bias a 6L6GC hotter than 50%
     
  13. Blue Strat

    Blue Strat Member

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    Please accept my condolences. :cry:
     
  14. Jerry Glass

    Jerry Glass Member

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    I'd say you have the better information then.

    I'm not a warranty shop and have only had a handful of these in that were past their warranty (of course). Those few I have had in did have lower voltage than the 460 to 470 you speak of...normally I wouldn't remember that sort of stuff but I own a 66 SR and for some reason it stuck in my head.
     
  15. phsyconoodler

    phsyconoodler Member

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    Quote:"Please accept my condolences. :cry:"

    Ha Ha Ha! It isn't that bad....really.They have great support online.
    no,really.:sarcasm
     
  16. guitarcapo

    guitarcapo Senior Member

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    I have two meters. Neither reads higher than about 510 volts. Both are Radio Shack. One cost about 15 bucks. The better one cost 50 and can measure caps too. If you read my post carefully you'll see that I stated neither can read HIGHER than the low 500's.... not lower.

    As for the calls for customer service...I think the warranty is a bit voided after gutting all the PC boards and rebuilding the amp. I bought it used about 8 years ago. That ship has sailed.

    I appreciate some of the advice here...Some not so much.
     
  17. phsyconoodler

    phsyconoodler Member

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    OK,you still haven't mentioned if you changed the batteries yet.Bad batteries can give very erroneous readings.
    With stock transformers the voltage should not be that high so that sends up a red flag right away.But even so the amp should still sound fine.what is the bias set at,what are the preamp plates at?Etc.etc....
     
  18. RussB

    RussB low rent hobbyist Silver Supporting Member

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    The customer service is in regard to the tech that gutted your amp. What's he got to say in all this?

    If you are going to be working on amplifiers, you need a good meter. You comment that neither will read much above 500v makes no sense unless the batteries are weak, the meter's are damaged or you don't know how to use the meter
     
  19. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Please post some good pics of the work. I'll bet we can find any issues
     
  20. LarryN

    LarryN Member

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    Meter wouldn't explain the "angry hum".
     

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