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Thread: Gibson GA45RVT

  1. #1
    Member boog's Avatar
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    Gibson GA45RVT

    This is my first gibson tube amp experience, I've never dealt with the "death cap" or had to swap out a cord.
    Just want to double check.
    C40 is the death cap?
    remove it and the wire going to the transformer from the same section of the switch, and leave the rest? black wire on the right, white left up from the plug on the schem below, and of course grounded to the chassis.

    Click image for larger version. 

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  2. #2
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by boog View Post
    This is my first gibson tube amp experience, I've never dealt with the "death cap" or had to swap out a cord.
    Just want to double check.
    C40 is the death cap?
    remove it and the wire going to the transformer from the same section of the switch, and leave the rest? black wire on the right, white left up from the plug on the schem below, and of course grounded to the chassis.
    C40 is indeed the death cap. Snip it out, and embark on a cap swapping rodeo of epic proportions for the rest. You can pretty well count on all the electrolytics being kaput by this time, and if they aren't, soon will be. Disc caps & films as well. I used to hate these amps, until I found that only a thorough, time consuming overhaul is the solution. They can be made to sound pretty good, but it takes a lot of patience. And solder. Don't forget some of the suspect caps are on the back of the tag board, you may need a dentist mirror to find 'em. Good luck!

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  3. #3
    Member boog's Avatar
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    Thanks, just wanted to make sure, that wire looks like it can go too?
    I already have the replacement electrolytics, I'm just trying to get it running for a friend, I've read they don't sound very good unless a few of the T filter networks (I think it said) are removed.

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    Lifetime Member Enzo's Avatar
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    Once the cap is gone, the wire doesn't go anywhere, why waste more time with it? But yes, you can do without the wire to S5c. But is it a real wire or is it just a jumper up to S5a on the same switch assembly?

    I never cared much for the old Gibson amps, that little narrow eyelet board with parts on both sides... I used to snip the wires off a backside part, fish it out from behind, then mount the new one on the near side. The parts don't care, and it saves me a lot of effort.

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    Member boog's Avatar
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    it's just a jumper, I hadn't taken a close look at the switch, I left it in, didn't want to risk breaking the switch pulling it out, and like you said it would be a waste of time as it's not doing anything with the cap gone.
    The owner doesn't want to invest a lot into it (almost didn't get the go ahead on replacing caps) so after the new electolytics are in and if it works, it's going back. all electros were original except the main 20+20 500v which was an old replacement, one of the other multis was bad, and I wouldn't agree to just change the one and not put a grounded cord on it.

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    Member boog's Avatar
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    Got the electrolytics swapped, and it powered up and made sound on the normal channel for a few seconds before I shut it down do to one or all of r57, 58, and 60 getting very hot, haven't taken any voltages yet.

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    Lifetime Member Enzo's Avatar
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    Um, those sound interesting, I wonder where they might be in the circuit. If only we had a schematic...

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    Member boog's Avatar
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    sorry, forgot I didn't post the whole schematic earlierClick image for larger version. 

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  9. #9
    Lifetime Member Enzo's Avatar
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    DO they still get hot in standby mode?

    V7 is a 0A2 glow tube. It is the tube equivalent of a zener diode. 150v. If it is shorted, those resistors would burn. Make sure that is the type tube in that socket. And is it glowing purple inside?

    Determine exactly which resistor or resistors is/are getting hot. It matters. Node B for example runs the reverb, and if that reverb transformer shorts to ground R58, 60 will get hot, but not R57.

    And make sure none of the new caps are wired in reverse.

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  10. #10
    Member boog's Avatar
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    They are getting hot in standby.

    V7 is an 0A2, doesn't show a short, but I haven't looked for the glow.

    58 and 60 are getting hot, reverb transformer isn't showing a short to ground.

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  11. #11
    Lifetime Member Enzo's Avatar
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    58 and 60 are getting hot
    So R57 is not?

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    Member boog's Avatar
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    57 is not, I'm only turning it on maybe 15 seconds at a time, the other 2 heat up quick.

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    Member boog's Avatar
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    Ok so I screwed up and had c34b reversed, now that's corrected, now all 3 of those resistors are getting pretty hot(maybe normal?) here are the voltages I'm getting.

    Click image for larger version. 

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  14. #14
    Lifetime Member Enzo's Avatar
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    Voltages look real close. Those are 5w and 7w resistors for a reason, expect them to warm up.

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    Member boog's Avatar
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    All seems good, been playing it off and on since my last post, it doesn't sound as bad as what I had read made it out to be, I think the owner will be happy with it.

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