1966 Fender Pro Reverb - No Sound - Rectifier tube?

Discussion in 'DIY Amp Forum' started by ianmccallum, May 9, 2021.

  1. ianmccallum

    ianmccallum New Member!

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    Hey guys,
    my main amp recently made some popping sounds, with a guitar plugged in or not, and lost sound of the instrument when plugged in.
    I turned the amp off immediately after snapping a quick picture of the tubes.

    I noticed the rectifier tube looked to be glowing brighter than the rest and looked to be burned out.

    Normally I'd always just send my amp to a tech, but given the circumstances of the pandemic in Canada everything has become more difficult.

    Would anyone give me advice on whether I should just replace the rectifier tube or send it off to a tech, I have a fairly technical background and have a degree in engineer, however I like having tech around so try to support them when I can.

    Thanks in advanced.
    Ian
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  2. Meghans Dad

    Meghans Dad Strat-Talker Gold Supporting Member

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    I'm surprised no one has not proffered any advice yet! I am no tech, but if there was no mojo smoke coming out, I'd trying swapping out the rectifier tube first. Where I'm at, techs are expensive, far away and busy.
     
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  3. CB91710

    CB91710 No GAS shortage here Double Platinum Supporting Member

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    The difference in glow of the tubes doesn't mean anything.
    As long as the plates are not glowing, differences are normal... that's just the heater.
    If it is making actively "popping" sounds with nothing plugged in, that's not good.
    Let it cool down, unplug and re-seat all of the tubes, then bring it back online.

    If it still does it, then start narrowing it down by removing tubes one at a time, starting with V1 (12AX7 at the very side of the cabinet), and work toward the power tubes.

    Being a '66, if it's never been worked on, it may be time for an overhaul.... re-cap, new resistors, etc...
     
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  4. fezz parka

    fezz parka fezz parka

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    In addition to filter caps...snap crackle and pop is plate load resistors going south. 100k 1/2 watt carbon comp resistors. Replace all of them with metal film. It's the B+ rail. No mojo is there...so ditch the CC's.

    It's an old amp. They need to be maintained. Just like a '66 Mustang.
     
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  5. CB91710

    CB91710 No GAS shortage here Double Platinum Supporting Member

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    And like a '66 Mustang, it'll last as long as it is maintained.

    Unlike a 1950's TV, these rarely go so far south that they aren't worth overhauling.
     
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  6. myredstrat

    myredstrat Senior Stratmaster

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    Don't know who your amp tech is but there is a fellow who lives in the Bloor West Village area who does some work on vintage amps for L&M at his home. Of course I can't even remember his name or where I put his number. I do recall phoning L&M service and actually got the info from them, but who knows if they will do it again
     
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  7. rolandson

    rolandson Dr. Stratster

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    I'd be prone to suspect the filter caps too, and plate resistors... that's exactly what it sounds like.

    Because the filter caps, I'd weigh the advantantage of powering it on again, against the potential harm doing so could cause. It's only old, be a shame to kill it.

    Take it to the doctor, let the doctor tell you.
     
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  8. Ampedup

    Ampedup Strat-Talker

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    Pretty common in old amps is simply a solder joint has cracked or broken. If you open it up and poke things with a wood chopstick you'll hear it (with the power on) just have great respect for the voltages, they can kill you. If you have to solder a joint look up how to discharge all your caps,(especially the big hidden ones ) other wise you will shock the hell out of yourself.
     
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