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SVT VR problems

S

schridb

Mar 13, 2012
25
0
#1
Hmmm,
So the other night during rehearsal the amp kicks into standby mode and won't come out of it. So I found JohnK's jumper fix that bypasses the relay on the standby. I was going to do that this weekend but now I have a different problem. After about ten minutes the volume will drop to almost nothing and then nothing and then a loud hum. I can unplug everything from the inputs and it still does it. Volume controls don't affect it. And it isn't the speaker cable or the cab. Anybody know what this might be? The power tubes are about a month old so they should be good.
 
#3
schridb said:
Hmmm,
So the other night during rehearsal the amp kicks into standby mode and won't come out of it. So I found JohnK's jumper fix that bypasses the relay on the standby. I was going to do that this weekend but now I have a different problem. After about ten minutes the volume will drop to almost nothing and then nothing and then a loud hum. I can unplug everything from the inputs and it still does it. Volume controls don't affect it. And it isn't the speaker cable or the cab. Anybody know what this might be? The power tubes are about a month old so they should be good.
Click to expand...

I don't fix problems overseas.
I don''t repair your amp overseas.
I don't do anything overseas.
But I'd suggest a technician that's not overseas.
 
#5
floridagatorfan said:
why being a Jackass man?
Click to expand...
queen-elizabeth-this.jpg
 
#6
Hi.

Tech time.

Plain and simple.

The symptoms You're describing does not point into tubes IME.
Then again, descriptions over the kbd are bound to be rather vague, so reseating could solve the problem. At least temporarily.

OTOH if You want to make the tech happier by allowing him/her to charge you for more of their time, pop the amp open and start repairing it DIY style.

Regards
Sam
 
#7
schridb said:
Hmmm,
So the other night during rehearsal the amp kicks into standby mode and won't come out of it. So I found JohnK's jumper fix that bypasses the relay on the standby. I was going to do that this weekend but now I have a different problem. After about ten minutes the volume will drop to almost nothing and then nothing and then a loud hum. I can unplug everything from the inputs and it still does it. Volume controls don't affect it. And it isn't the speaker cable or the cab. Anybody know what this might be? The power tubes are about a month old so they should be good.
Click to expand...

I hope I understand all the words.

1) plug your instrument into the PowerAmpIn-Jack and check the power amp.

2) If power amp works, plug your instrument into channel-2 and check it.

Checking preamp without power amp:

3) solder a short cuttened plug and plug it into PowerAmpIn.
Then plug any preamp into PreampOut and do a check to channel-1 and channel-2.


My be the fault is only a dead tube in channel-1.
 
#8
T-Bird said:
Hi.

Tech time.

Plain and simple.

The symptoms You're describing does not point into tubes IME.

Sam
Click to expand...

A muted amp after 10 minutes running.
I hope it's nothing else but a bad tube in the preamp section.


If the problem derives from the power amp I'd advice not to power up the amp any more.
In some circumstances a defect in the power amp section can kill the pentodes.
 
#11
The TB community generally does not recommend or endorse venturing into your tube amplifier. Although I enjoy DIY-ing my repairs(not tube amps) when possible, it IS worth noting that tube amps contain some unforgiving voltages and tight working spaces. On top of the fact that repairs require a pretty specialized pool of knowledge, and I think it is fair to assume that a tech is your best bet here.
 
#13
Totally agree on the idea of no DIY in this case.....

Basically, if you need to ask what you asked, you have pretty much shown yourself to be "not a candidate" for DIY.... Otherwise you would be reporting that you had already checked the jacks, tubes, wires, voltages, etc, and would be looking for more detailed suggestions....

That said, for a tech, I would expect tube amps to be jam...... I'd rather repair almost any tube amp than most new SS units with densely crowded PWBs full of surface-mount (SMT) parts.... I CAN do either one, but the tube amp has its schematic pretty much laid out for you right there...... parts are not the size of raw sugar crystals, etc, etc. For the multi-layer SMT PWB, you want a schematic and part reference.
 
#14
I have no intention of opening this beast up. Other than to troubleshoot preamp tubes. Was just checking to see if it might be an easily diagnosed problem. Unfortunately, I think it points to a transformer. Oh well. Gonna have to spend the cash. My backup just comes nowhere close to the sound of a VR. I dream about it.
 
#15
Does NOT necessarily (or at all) point to a transformer yet...... No need to focus on the most expensive part in the amp (and incidentally, probably the toughest part also).

Lots and lots of other possibles which are more likely. Take to a tech, AND DO NOT SAY ANYTHING ABOUT WHAT YOU THINK IT MIGHT BE. Just explain what it does, and let them figure out the issue.

Most techs are quite honest. But in case of a borderline guy, no need to let him think that he may have "a live one" on the hook..... Prepared and "prequalified" for a major repair bill....
 
#16
I wouldn't assume that because the tubes are only a month old that they should be good. New tubes that haven't been subjected to a quality control burn-in test period, can fail. It happens.

Folks often assume the worst case scenario and think that their transformer is bad. A transformer failure is relatively rare. There's a long list of other possibilities that need to be considered first.

As Jerrold said, don't help with suggestions. It might wind up costing you more.
 
#17
IMO, way more than likely, it's NOT a transformer issue.
send/receive jacks, a loose or oxidized internal connector, cold solder connection or a tube would be the first things that i'd check. once a tech gets it to repeatably exhibit it's problem, it should be a relatively simple and inexpensive fix.
 
#18
I've talked to my two favorite local techs about SVT's, and they both have said that they have never had to replace a transformer in one. I suspect a tube gone wonky.
 

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