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Amps noisy after warming up

Discussion in 'Accessories / Connections' started by EdWray, Jul 23, 2009.

  1. EdWray

    EdWray Active Member

    I have a '67 twin reverb and a '68 ampeg V-2. Both amps sound great until they warm up; then they start making little crackly noises. Any ideas, solutions? Thanks
     
  2. moonbaby

    moonbaby Mmmmmm Well-Known Member

    A couple of questions here:
    When was the last time you replaced any of the tubes in these amps?
    Do you know how to work on a tube amp without KILLING yourself?
    Starting with the Twin, I'd check the preamp tubes for microphonics, which can make the amp "spit" like that. You do this check by letting the amp warm up, setting the volume control on each channel to a moderate level (say, 9 o'clock) and then tap on the tubes with a pen or pencil. Can you hear this tapping through the amps' speakers? That microphonic tube may very well be the culprit. But so can a myriad of other components, like the carbon composition resistors, old tube sockets with dirty pin sockets, and even a bad power tube.
    I had a V-4 that did that, and you can slap the side of the head and it would stop the noise-temporarily, of course. THAT ended up being the grid resistors that went to the power tubes.
    The bottom line here is that there are a lot of things that can make an amp "crackle". If you are not experiences with high-voltage electronics, after your initial tube-tapping test, find an experienced tube amp tech (preferrably one old enough to have lost a few teeth!) and let him/her hash it out.
     
  3. EdWray

    EdWray Active Member

    Thanks for the response, Moonbaby. The V-2 has mostly the original magnavox tubes. Some are nearly new, replacing ones that went microphonic. The twin has vintage tubes that I purchased supposedly NOS in the preamp section. The power tubes probably don't have more than 20 our 30 hours on them. Both amps were gone through by the tube amp tech that works for the guys that make tone tubbies and they both worked perfectly for a few months. He thoroughly cleaned the pots and tube sockets and replaced some of the grid resistors in the twin. He also recapped the power supply. He rebuilt the reverb circuit in the V-2, cleaned it, reset the bias. Smacking the amps does temporarily stop the noise. I will try the microphonics test and replace any tubes that do not pass. I understand the lethal danger inside and do not know exactly what not to touch to keep from killing myself so if replacing tubes does not fix the problem I will take them back to the shop. I replaced one of the grid resisters once in the twin but I was taking a risk, for sure. I'm not sure about his teeth but he's definately old school and considered one of the best tube amp techs in the bay area with something like 30 years experience. I'm sure he'll know how to fix them if I can't.
     
  4. BobRogers

    BobRogers Well-Known Member

    On vintage amps like this I wouldn't do anything more myself than change the tubes. Especially when you have a first-class tech locally available it is worth paying for that expertise. I think you just have to resign yourself to taking the amps into the tech regularly for maintenance. Happens to humans when we get old too.

    If someone wants to work on tube amps there are plenty that were built in the last twenty years that you can experiment with to your hearts content.
     
  5. RemyRAD

    RemyRAD Guest

    Some of these older amplifiers utilized vacuum tube rectifiers. Like any other tube, they can get noisy imparting noise upon your power supply rails. Some folks have occasionally modified their amplifiers to remove the vacuum tube rectifier in favor of a selenium or silicon rectifier. You always want clean power to power your tubes. Old capacitors can become leaky and cause similar problems. Yes, if things do need to be restored/rebuilt overtime for like new performance. Otherwise you can enjoy that vintage sound with all that crackle pop to remind you that it's vintage.

    Rice Krispies
    Mx. Remy Ann David
     
  6. nbarts

    nbarts Guest

    Check tubes first.
     

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