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Ampeg SVT-VR blows fuse and 2 power tubes HELP!

dw1003

dw1003

Mar 18, 2008
34
7
Claremont CA
www.finch-music.com
#1
Hi

I'm on tour and my head blew a fuse and now I've noticed that the middle two power tubes are dark.
The tubes are well used and abused (I tour and record regularly)

The venue last night has sketchy power...

This amp has been a workhorse and I've never had an issue like this.

I replaced the fuse and the amp powers on but those middle two 6550's are down.

should I just buy and emergency pair of 6550's? I've got 10 shows left on tour

Thanks,

Daniel
 
#2
The venue's power may have caused your amp to blow. There is a screen resistor for each power tube on the power tube board. These resistors act like a fuse in the event of a problem. It is possible that these need to be changed, in addition to the tubes.

You should have your amp looked at by a tech.
 
#3
Also -

I could be wrong, but I don't think you can just replace a 'pair' of power tubes in an SVT. There are two triads (3) and I think even if it's just one tube that goes bad on you, it's recommended to replace that triad with another matched set of 3.
 
#4
jason the fox said:
Also -

I could be wrong, but I don't think you can just replace a 'pair' of power tubes in an SVT. There are two triads (3) and I think even if it's just one tube that goes bad on you, it's recommended to replace that triad with another matched set of 3.
Click to expand...

The two middle tubes would be one of each triad.

Emergency on the road you might get by with just two tubes, but if the old ones have "gone dark" that is a worry as well as the resistors mentioned above. Best advice get a backup amp until a tech can check it over.
 
#6
Thanks everyone, I won't have time to have a tech look at it, but can purchase a new set of tubes in Austin tomorrow... My only worry is if there is an issue with the screen resistor that caused each of the middle tubes to go dark, I could blow another couple tubes. Is there a way to visually inspect the tube sockets to see if there's an issue?

I have a back up head of course... Just not an SVT VR... So it's not cool

Thanks Again!
 
#7
You'd have to pull the power amp out to see if your resistors are blown. I don't know a whole lot about amps, but if you did blow a resistor, I would have to think that your new tubes just wouldn't work and wouldn't get damaged. It's possible it might have blown but it's not something that happens every time you have a power tube failure. I'm sure someone qualified will be on this thread soon to tell you how best to proceed.
 
Last edited:
#8
The resistors don't "blow the tubes" they act as a safety fuse when a tube blows to help prevent major damage and allow operation to continue without the tube(s). You keep saying they went dark, that is troubling.

If those two tubes blew their resistors, the new tubes should "light up" but will not operate and will not bias. If new tubes do not light up, STOP trying to use the amp until a tech can get in there.
 
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#10
dw1003 said:
Thanks everyone, I won't have time to have a tech look at it, but can purchase a new set of tubes in Austin tomorrow... My only worry is if there is an issue with the screen resistor that caused each of the middle tubes to go dark, I could blow another couple tubes. Is there a way to visually inspect the tube sockets to see if there's an issue?

I have a back up head of course... Just not an SVT VR... So it's not cool

Thanks Again!
Click to expand...

if you have time you could call chuck at guitar rez in austin, (512)478-0095
he might not be in or he might not have time but i suspect he might find some time to give it a quick look. he's a good tech.
 
#12
I do agree that the best move is to take the amp to a tech but with 10 shows left on your tour that's not an option. At this point if I were you I would replace the power tubes. If the same 2 blow out again then you have no choice but to use the backup. At the end of the tour take the amp to your guys and have him replace the 2 tubes to match your new set so you won't loose out on that much money.
 

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