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tube guys: svt chop up Q

Discussion in 'Amps and Cabs [BG]' started by staindbass, May 15, 2011.

  1. Selta


    Feb 6, 2002
    Pacific Northwet
    Total fanboi of: Fractal Audio, AudiKinesis Cabs, Dingwall basses
    Johnny, if you do end up going through with this, keep us updated on it. I'm definitely watching this, interested to see what/how things turn out.
  2. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    6C4 was never intended for audio, so nobody bothered to make the innards stable against microphonics....

    if the OP has an SVT, would it not be simpler to come out of the slave out and try the thing thru a power amp? He already knows it needs a volume boost and is apparently going to provide that.

    if the first stage tube is removed in the power amp, there won't be any issue with the signal going thru power amp...... just plug in a speaker to load the output "just in case".
  3. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    My bad; was thinking that this was for a studio application but now realize it's about live sound
    I spent a ton of time trying to build a 1,000 watt SVT. Even after trying a few different compressors in the chain as well as an old QSC and a Ampeg power amp, I was never satisfied with the SVP-CL.

    Was completely convinced that the entire 3-D clairty, wide soundstage, big fat meaty tone was all about the power tubes (cabs were Bergantino and a 1x15; basses were a 60 P, 70's J, and a SR). After a few hybrids have settled on the Mesa WA; still 300 watts but way lighter and really sounds like my CL. Am told the DI sounds great

    Anxious to hear how this pans out for you.
  4. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    In the SVT, the voltage going from the power amp to the pre-amp is from node B in the power supply, about 462 VDC. On the pre-amp, at the plate of the 6C4, the voltage should be around 300 VDC. The voltage is dropped through the 8.2K resistor. (462-300)/8.2K= ~20milliamps. This is the voltage and current that feeds all the other pre-amp tubes. As you mentioned, you will also need to supply the heaters with about 1.5A at 6.3VAC

    The ground system in Ampeg amps is different from most amps. The ground point for the entire amp is at an input jack. This is the only ground. From here a bus runs to the main filter caps. The filter caps are isolated from the chassis. It seems strange but it is quiet.

    I would test the pre-amp out into something else to find out if the SVT pre is going to give you the sound that you are looking for. Maybe what you like is from the power amp. If the pre gives you the tone that you are looking for, you can go from there.


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