• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Another Ampeg SVT-VR channel two problem

#2
Wow, never heard that before! Doesn't happen on my 69, and I don't ever recall hearing it on any VR I've tried. One guy on that Youtube link suggested that the pre tube is microphonic. Don't know about that, but worth a shot. I believe it would be V2.
 
#6
The first thing to look at is the channel 2 tube as Jimmy said. A bad tube can cause that type of hum. On the VR, the tube in question is a 12AX7. They call it V5 in the circuit. To test the tube, you can swap it with a 12AX7 from channel 1. Just don't forget which one was originally were.

Some people like to use a high quality, low noise tube like a 7025 in this position since it keeps noise to a minimum. The problem is, the preamp tubes in this amp are located inside the chassis on the top. You will need to CAREFULLY remove the pre-amp chassis to gain access. This takes a bit of work.

If you haven't done this before, the easiest way to do this is to remove the top two metal cabinet corners on the back and the bottom two on the front, remove the chromed back panel, and pop off the front grille by pushing on the left or right side from the back (I use a wood dowel but anything similar will do), disconnect the pre-amp cables, remove the four screws on the top of the cabinet, then slide out the pre-amp chassis.

It helps to take lots of pictures to make sure that you have a record of where everything goes. It also goes without saying, don't touch anything that can give you a shock. The capacitors inside the amp store enough energy to give you a nasty shock.
 

Latest posts

Top Bottom
Back