Ampeg V-2 low volume issue

[psycle_1]

I have an Ampeg V-2 that is suffering from very low volume. I can flip the standby switch and for half a second I get what I would consider normal volume before it fades back to a whisper. I checked voltages based on the test points on the schematic and all seem within tolerance. Any help would be greatly appreciated.

[Chuck H]

Can you post a legible schematic?

My first thoughts. Voltage readings only go so far and I can't know if some relevant voltages are skipped on the schematic unless I see it. You may still have a bad tube/s, failing power supply filters, a bias failure or some combination of all these things with any amp of that age.

[52 Bill]

My first thought would be a leaky coupling cap. It would make sound to start until enough voltage started to leak through and cutoff the following grid.

[Enzo]

If you then cycle the standby off and back on, do you get another half second?


A symptom like that makes me think some grid is not terminated and a charge builds up there.

Here are some schematic links. They are Joe Piazza's, so they won't have part numbers or voltages, but best I can do from home.
http://bmamps.com/Schematics/ampeg/Ampeg_v2preamp.pdf
http://bmamps.com/Schematics/ampeg/Ampeg_v2powamp.pdf

[Diablo]

I would do the pop test, starting at the output tubes and work your way back toward the preamp input tubes. The pop should get louder as you go towards the preamp. Connect your DVM to a good ground and with the red lead touch the socket pin for each tube grid. When you touch the grid, it should pop. At the stage that you don't get a pop, or the volume is quiet - that's where you have a problem.

[psycle_1]

Here is the schematic from the top cover of the chassis.

[psycle_1]

Enzo, yes, I do get another half second or so when I flip the standby switch again. Sometimes after it fades it will be louder than it was previously.

Diablo, I will try the pop test and report back.

Thanks for the help guys. I'm getting into repairing amps, and this is only the second Ampeg I've worked on.

[g1]

Here's a more readable schematic for the combo version, aside from the speakers, I think they are the same.
Try wiggling the preamp tubes around. I find a lot of symptoms like this are due to dirty/oxidized sockets, or bad solder connections at the preamp tube sockets.

[psycle_1]

Did the pop test. One of the output tubes "pop" had a lower volume than the other. First thought was a bad tube. I was going to substitute a known good pair of 6L6's in just to finish the test. Pulled the tubes out and noticed the sockets were pretty corroded. I figured what the hell, lets see what some deoxit will do. Put a drop on each pin of the power tubes and inserted into the sockets about 10 times. Fired the amp back up....

No more volume drop! (Or at least not that I can tell, wife is napping right now. )

Shut the amp off and did the same with the preamp tubes and went ahead and did the power tubes again. Still no volume drop. Amp is sitting on the workbench powered on while I wait on the wife to wake up.

[psycle_1]

2 hours later....

The amp is completely back together and functioning perfectly. Thanks for the help guys! I look forward to hanging out on this forum and learning some things! Just go easy on me. LOL

[Chuck H]

2 hours later....

The amp is completely back together and functioning perfectly. Thanks for the help guys! I look forward to hanging out on this forum and learning some things! Just go easy on me. LOL

It's kind of funny that I failed to mention cleaning the sockets. I'm often the first to say it. I think it's because the symptoms seemed to indicate a consistent change in current or voltage. I missed my shot to nail it on the first post, Drat! I'll be ready next time. Glad it was an easy fix.

[psycle_1]

It's kind of funny that I failed to mention cleaning the sockets. I'm often the first to say it. I think it's because the symptoms seemed to indicate a consistent change in current or voltage. I missed my shot to nail it on the first post, Drat! I'll be ready next time. Glad it was an easy fix.

Yeah, that's usually one of the first things I do when I get an amp in, but I was immediately thinking power supply issue based on the age of the amp.