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Ampeg V4BH biasing?

Discussion in 'Amps and Cabs [BG]' started by superfly, Nov 24, 2004.


  1. superfly

    superfly

    Aug 4, 2004
    I ended up buying the Ampeg V4BH that I mentioned in another thread. All tube, 100 watts (enough for me), mint condition 2 yrs old. Sounds great, warm, smooth.But this is my first tube head, so I really don't know how its supposed to sound. It has Groove tubes. Are these factory from Ampeg?
    anyway, I want to take it into a tech for a service and a go through.
    I was reading about biasing in the owners manual and online. How exactly does a tech bias this particular amp. I looked in the chassis, and dont see any trim pots, or anything. Just tubes and transformers. Will he have to drop the guts down from the chassis? Is there something inside the guts to adjust? Maybe this amp is self biasing? Don't worry, I'm not gonna try this myself, I'm just curious how this is done. :rollno:
     
  2. JonB

    JonB

    May 27, 2003
    Indianapolis
    Mine's about the same vintage and had Sovteks. Actually, they were 5881's instead of 6l6's. Probably they use tubes from various suppliers.
    There is one trim pot accessible through a small hole near the power tubes. Just one - so you need to get matched quads when replacing tubes. I bought a "Bias King" meter for about $100 and check the bias periodically. It isn't hard to do, but if you're not comfortable around electronics, you're wise to have a tech do it for you.
    Once the tubes burn in, they don't change much.
     
  3. superfly

    superfly

    Aug 4, 2004
    It looks like one of the power tubes is bad. I get alittle crackle from time to time. I gently tapped the tubes with a wooden dowel and one of the tubes causes a crackle when tapped.
    So off to a tech for tubes and biasing. Probably a good idea anyway since I bought it used.

    Anyone know a good fast amp tech in So California?

    Would replacing one tube be ok for now? Or do I need to a whole set? If I replace one tube, would it need to be biased?
     
  4. JonB

    JonB

    May 27, 2003
    Indianapolis

    This could be pin corrosion. Some cleaner spray might take care of it. The tube might be fine. Try switching the tube with the one next to it to see if the problem follows the tube.


    Replacing one tube isn't a good idea. Even if you find the same brand, chances are it won't match the others.

    Power tubes aren't individually biased on this amp, as I pointed out earlier. There is only one pot for all bias voltage. It could be converted to individual bias - at some expense. Plus, this would void whatever warranty remains.