Clueless Idiots and High Voltage Vacuum Tubes Really Do Mix!

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Dilapidus is a software engineer who loves old school amps.


11 Comments so far ↓

  • Rob

    Can you email me, I am working on a 1962 GA5 Skylark amp, was looking for a gut shot in its original form before any mods done, do you have one? Thanks!

  • Patrick

    I stumbled across your blog searching for information regarding a Gibson GA5t amp I recently acquired. Besides the information about the amp, you have some very interesting topics on your blog. I now have it book marked.

    Keep up the good work!

  • Patrick

    I do have a question regarding how to go about trouble shooting the tremolo oscillator circuit for my GA5T amp as it is not working. I do have the schematics, but I am not certain what to do.

  • Dilapidus

    Unless there is a voltage obviously way out of whack somewhere, I would start tracing/replacing on the tube, switch, caps and resistors.

    The oscillator output goes right to the bias of the output tubes. This is probably 16v with the trem off. I think it will increase with the oscillator 10v (to 26V and then back down to 16v) all numbers +/- 20%.

    If you want to describe more about the problem and how the efforts are going, send an email and I’ll start a thread here to cover the conversation.

  • Patrick

    The individual that I purchased it from had the power cord replaced with the three prong cord and had the caps replaced that needed replacing. The one thing that was not repaired, for whatever reason, was the tremolo. The PO stated it works intermittently and the tech said the problem was with the tremolo oscillator. As I have chance to pull the board and look, I am working off of the schematic and what I have read so far, the schematics are sometimes way off what is actually built. The amp sounds really nice. I would like to get the tremolo working and I am not sure where to start.

    I am all ears.

  • Patrick


    Today I contacted the tech that worked on the amp and he said he replaced a few caps/resistors and switching the 2-prong for a 3-prong plug. He thought the tremolo oscillator might need the caps replaced.
    I removed the board and took a number of pictures and the schematic that resembles the layout I have is this one,
    Is there a way I can send you these pictures to get your read as to what I have going on and possibly what steps I should take to troubleshoot.


  • tony

    Looking for Chris Murphy- Ransom from Csun said you might have some VBB and electronics.
    Rally 200 electric vehicle.

  • Dilapidus

    Sorry.. Don’t know Chris Murphy, maybe he’s the artist that calls some of his work Paleoelectronics?

  • M.H.

    Hi, I ran across your ga-5t metalist(single 6bq5) schematic when searching for a circuit to use converting an Akai Terecorder. Could you please tell me the value of c1 and where sw-a is located on the amp. Sw-b I won’t need(3prong chord). I can’t tell from the few photos available. Thanks for any help. M.H.

  • Dilapidus

    I will have to check tonight, i’ll get back to you.

  • Dilapidus

    And then I didn’t. I’ve set a reminder for tonight. Sorry about that.

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