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SVT Classic Static Problem

S

seidler

Dec 18, 2005
98
3
71
www.myspace.com
#1
I just bought a used SVt Classic Made in USA. It sounds great when I first start playing it (whether or not it warms up for 30min or I play as soon as it comes on) and after 10 minutes or so it starts breaking up with major static and or the volume drops off dramically. This is whether or not I have the gain set at 7 and the master at 2 or the gain at 4 and the master at 4. Using the 0db or -15db input or changing basses from passive or active makes no difference.
I have no idea how old the tubes are. I tried reseating the tubes (removing and reinstalling them). The bias loghts are green. The system has a light coat of dust on it inside. I have read about a ground problem and wonder if this could be caused by that and if so where is the offending ground cable?
Thanks
 
#7
i would bet it is a problem with where the ground on the preamp board attaches to the chassis. i had the same problem with one of my CL's as did another TBer. i added a washer over the standoff that the preamp board ground sits on to improve the contact area which solved the problem. give that a try. pm me if you need help.

JR
 
#8
I would almost bet money it's a 12AX7 gone bad. I just had a Fender Super Reverb with that problem and the new tube fixed it. But whatever it is it's probably not an expensive fix.
 
#10
They're pretty self-explanatory how to open them up once you take the grill off. But if you haven't done it before, make sure to only touch the outside of the chassis and don't touch any capacitors or parts like that because they can still hold a lethal charge even when unplugged. You can short them out with an insulated screwdriver, but I hate doing that. Makes a pop that scares me ;)

But if it's a tube like I think it is, any music store should carry 12AX7's. I prefer to order my tubes NOS from www.vacuumtubesinc.com because I like the old American and English tubes. They are a lot more reliable. But you can get tubes anywhere. If you get Russians, I suggest sticking with a company like JJ or Sovtek for reliability.
 
#12
I would have the tubes tested and only get what's broken replaced. If you have no access to a tube tester, you can try swapping the 12ax7's around and see if the static goes away. That might at least narrow it down and let you know if it's a tube.
 
#13
Oh, one other thing you might want to try...get some contact cleaner and spray out the tube sockets, then push the tube in and pull it out 4 or 5 times. You might have some dirty sockets.
 
#16
Took it to the local Ampeg repair center. 10 days later they said it was done and had a bad power tube. They replaced the 1 tube. Said it was arcing. Took it home and same breakup/static. So bad you can't play it. It might go away for 5-10 min and then back. Seemed to get worse when it got hot. Bought 6 power tubes and it was still bad. Took it apart this morning and and re-soldered all joints (we maye there were 10 or so if the approx 120 I could not get to). Put a washer on the ground for the main board ground post as suggested above. It sounds great!! Awesome, fixed it myself. Now I am in practice heaven. Will never take the head out to gig, for that I will use my LMII and a cabinet, but for in the house jams and parties this thing rocks. Just too heavy to lug around.
 

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