Help to "Fenderize" reverb on GA-1 RVT

Discussion in 'Shock Brother's DIY Amps' started by NSB_Chris, Jul 4, 2019.

  1. NSB_Chris

    NSB_Chris Tele-Meister

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    Tested out OK and went to full volume. A lot stronger reverb now. No oscillation, but I do get some crackling at full volume. The B+ voltage is higher for this than the original, so I might try to lower the B+ and see how it does. I plan on putting it on the variac and dropping the voltage so that the B+ is closer to the original and see how it does with that. Might switch back to the original tubes I bought for it also and see what difference that makes.

    It still needs a few trim pieces around the front face, a handle and maybe a grill in the back to protect the tubes, but it is much closer now. First time wrestling with grill cloth and I did not do a very good job. It is a little "pillowey" but I might not even try to tighten it up.

    The master volume works, but I don't know why I would ever use it on this amp. Easy and fun test, but I would definitely not add the master. It will stay bypassed with this one. The tremolo intensity works and is useful. The bypass switch is nice because the intensity takes a step down when the intensity pot switch is engaged. The intensity works to dial in a subtle level of tremolo.

    IMG_3523.jpg IMG_3522.jpg
     
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  2. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    On BF type reverb circuits, do you also use the 3k resistor and 10uF cap?

    I’ve got some hum in my BF type build’s reverb that I’m scheming and planning to reduce.
     
  3. tubelectron

    tubelectron Tele-Holic

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    Yes, it would work too. C = 10-22µF 500V, R = 1.5-3.3K 1-2W.

    @JohnnyCrash : I dig your username, too funny and absurd ! :lol:

    You are progressing fine in your Maestro amp release, congratulations @NSB_Chris ! :cool::cool::cool:

    Please post the link to your separate thread, if it's still time to help... ;)

    -tbln
     
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  4. NSB_Chris

    NSB_Chris Tele-Meister

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    Always time to help. This one is trying to educate me as the issues were beyond my knowledge and experience to troubleshoot. Here is the other thread: https://www.tdpri.com/threads/problem-with-first-fire-of-ga-1-rvt-clone.977923/

    I will probably try playing this amp side by side with the original and do some tube swapping tomorrow night. It has been crazy busy for me the last few days ... work, sick dog to emergency Vet, redoing my main pedalboard to be ready for Thursday's jam session and building a new 2x12 cabinet for an amp I built previously. No rest for the wicked. Hope I can get the GA-1 RVT sounding reasonably authentic!
     
  5. NSB_Chris

    NSB_Chris Tele-Meister

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    Fun project and I have a nice little amp even if I fell short of reproducing the magic of the original!

    I switched out the preamp 6U8A tube for the original I purchased and it behaved much better at full volume. I A/B'd it with the original vintage amp. The one I built is a good sounding amp but does not stand up to the sound of the original. They both sound great at lower volume but the overdrive tone with volume above 8 is very different. My version is brighter with an edgier overdrive. The original has a more warm growl. Not sure if that comes from a true 7199 tube in the preamp or a 50 year old speaker etc. Could be that the differences in the circuit between the first and second gain stage and the way the reverb circuit interacts is responsible. I may purchase a true 7199 tube, rewire the necessary pins and see how that changes the sound. No option to reproduce the circuit exactly as I cannot find the right reverb tank, transformers, 2M pots etc. If it takes 50 years to get the amp to sound right, I won't live long enough to enjoy it :).

    On to the next project.....
     
  6. symbiotic

    symbiotic TDPRI Member

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    Try running your new amp into the old speaker/cabinet and see what you get!
     
  7. NSB_Chris

    NSB_Chris Tele-Meister

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    Good point. I was reluctant to do that because the speaker is wired directly and I will have to desolder at least one lead. Might just do that quick test before sending the original amp back to the owner.
     
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