Hey. So my 70's Ampeg V4 w/Reverb isn't making any sound. I powered it up and the amp turns on, tubes light up, but no sound when I take it off standby. Now I have a feeling the unusually cold weather might have something to do with this, as the amp was stored in my cold basement. We've been having single digit and negative temperatures for many days. I put my amp in a warm room hoping this will work. Gonna let it sit for a while. Anyone's amp ever not work when it's too cold?
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Nope - and I spent a couple years in a busy band that kept a backline, lights, and sound in a trailer full time in upstate NY... We never had any problems with the amps for guitar, bass, or PA - despite *a few* stretches of sub-zero weather, and doing about 150 gigs a year...
Hmm. I'm gonna try it again in a bit. If it doesn't work I guess I'll take it to a tech. Fingers crossed
Good luck - but before taking it to a tech, *I* would try patching an instrument cable in the effects loop, and if that doesn't work, try swapping a known to be good preamp tube in at least the V1 slot( the one closest to the input jack, typically)
I let it warm up for about an hour and now it works! I'm a little confused by this, but hey my amp is working
Intermittent problems are hardest to duplicate, diagnose, and repair.
However, they are the problems most likely to rear their ugly head when you least expect them. Like right before an important gig.
Signed,
Naysayer of Doom
It's tech time.
An amp that takes an hour to warm up, even from the deep freeze, before it starts working, has a problem.
When it wasn't working and you took the amp off standby did you see a difference in the power tubes and/or hear the thunk of the power amp? With the standby circuit arrangement on the V4 it's usually very obvious when you flip that switch. I've seen a lot of the 70s ampegs with failed power and standby switches and I wonder if you simply have a bad switch. Could be any number of other things as well, but something that you should have been able to hear very easily so I figured I'd ask.
It's also possible that the cold caused the jumper in the effects loop to contract, disconnecting the internal loop. When it warmed up, the metal expanded back, and made the connection. If this happens again, jumping the effects loop as mesaplayer83 suggests, would confirm that this is the problem.
The theory is good but the vintage V4B doesn't have an effects loop. It has a combination pre-amp out/power amp in jack but there are isn't a shunt that the signal runs though when a plug is not inserted into the jack like many other amps have. It's simply a Y tap between the pre and power amp.
Along the same line of thought though, cold contracts metal and it could be an intermittent contact. There are a number of possibilities. I would first reset the impedance selector switch, to make sure that contact is good. A common issue with these amps is a loose tube socket pin contact. If any of the small tubes slip in or out of their socket too easily, the tube socket contacts might need to be retensioned (pinched in a little tighter).
I would have a tech look at the amp. As was mentioned, there's a chance that it could fail again when you least expect it.
Along the same line of thought though, cold contracts metal and it could be an intermittent contact. There are a number of possibilities. I would first reset the impedance selector switch, to make sure that contact is good. A common issue with these amps is a loose tube socket pin contact. If any of the small tubes slip in or out of their socket too easily, the tube socket contacts might need to be retensioned (pinched in a little tighter).
I would have a tech look at the amp. As was mentioned, there's a chance that it could fail again when you least expect it.
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I agree - something is not quite there with your amp, and if you don't get it really fixed, it's likely to not work the next time you really need it to work.
No, I didn't hear the distinct "thunk" when I took it off standby. Also, I looked at the back of the amp and the power tubes were flashing blue on and off quickly, almost like they were struggling to work.
I understand completely. In the tube Hi-Fi realm, I had an Audio Research stereo power amp (a pair of 6550 tubes per side and crap-load of pre/driver tubes- totaling about 17 tubes!).
Damn thing would hum intermittently (low level, only distracting during quiet passages). Even after trying everything I knew and taking it to my EE mentor who was very well versed in "Classic Hi-FI Tube Amp 101", we could not duplicate the problem.
I moved three times during the ownership of that amp; every time I moved, it would perform flawlessly for the first week or so, then start acting up again.
Tubes and tube amps can sometimes be just darn weird like that!
Rule number one from my mental "Happy Amp" book- Always let ANY electronics acclimate to room temp before even plugging them in!
Damn thing would hum intermittently (low level, only distracting during quiet passages). Even after trying everything I knew and taking it to my EE mentor who was very well versed in "Classic Hi-FI Tube Amp 101", we could not duplicate the problem.
I moved three times during the ownership of that amp; every time I moved, it would perform flawlessly for the first week or so, then start acting up again.
Tubes and tube amps can sometimes be just darn weird like that!
Rule number one from my mental "Happy Amp" book- Always let ANY electronics acclimate to room temp before even plugging them in!
You should take it to a tech. There may be a marginal solder joint somewhere that contracted in the cold, and then made contact again when it warmed up.
Also, it's never a good idea to bring any electronic device in from the cold, and power it up right away. Condensation can form inside the chassis and cause things to short out.
Also, it's never a good idea to bring any electronic device in from the cold, and power it up right away. Condensation can form inside the chassis and cause things to short out.
Could be a contact that is recessed a bit by the cold then returns
at normal temp. Input or output jacks.
at normal temp. Input or output jacks.
A marginal solder joint is QUITE a possibility.
Same thing in my case as noted above- most likely a cracked resistor that physically "opens" as it heats up to operating temp (after settling from all the moving truck vibes!).
At least with a solder joint, simply reflowing the joints may solve the problem (unlike having to replace EVERY resistor).
