No sound on Peavey VT Classic combo amp

[bartesatan]

Hi!

I purchased a 1978 Peavey VT Classic amp a couple of months ago, but after one and a half band rehearsals, while I was still playing, it suddenly stopped making any sound. The power tubes still light up, but there is no sound whatsoever. I did replace the main fuse on the back just to be sure..

I did read somewhere that an HT fuse could be the problem to such a case, but looking at the schematics (http://www.adrsoundsense.co.uk/techn...assic%20VT.pdf), it seems to me there is only the one main fuse on the back. I don't know too much about this, but if any of you have any tips or know where to look to fix it, it would be highly appreciated!

[Dave H]

I did read somewhere that an HT fuse could be the problem to such a case, but looking at the schematics (http://www.adrsoundsense.co.uk/techn...assic%20VT.pdf), it seems to me there is only the one main fuse on the back. I don't know too much about this, but if any of you have any tips or know where to look to fix it, it would be highly appreciated!

All the PT secondaries are fused. I'd check them all. The HT fuse is F2 on sheet 3

[bartesatan]

Thank you for the very quick reply!
If I find and replace a broken fuse, what more could I do to prevent it from blowing again? Does it depend on which of the fuses it is?

[DrGonz78]

Check every one of those secondary fuses F2-F6, obviously F6 and F1 are not the issues since you have power to the amp plus the filaments light up. Yes it matters what fuses (if any) are blown to help proceed with a repair. Most times you will replace a fuse and turn on the unit only to find that the same fuse blows again. So I recommend to figure out what fuse(s) have blown (if any) and report back that information before powering up the unit. You said that you replaced the Main fuse on the back which would be F1 primary fuse. That fuse could not have been blown if you had filaments light up on the tubes and in fact you may have ZERO blown fuses in the amp. There are many other issues besides fuses that can cause the guitar signal to drop out.

[bartesatan]

Check every one of those secondary fuses F2-F6, obviously F6 and F1 are not the issues since you have power to the amp plus the filaments light up. Yes it matters what fuses (if any) are blown to help proceed with a repair. Most times you will replace a fuse and turn on the unit only to find that the same fuse blows again. So I recommend to figure out what fuse(s) have blown (if any) and report back that information before powering up the unit. You said that you replaced the Main fuse on the back which would be F1 primary fuse. That fuse could not have been blown if you had filaments light up on the tubes and in fact you may have ZERO blown fuses in the amp. There are many other issues besides fuses that can cause the guitar signal to drop out.

Thank you for the information! I will check the fuses and post on this thread when I have done so.

[Enzo]

And don't jump to conclusions, we could have a speaker/wiring problem instead of the amp itself.

As was said above, all the secondaries are fused. THE most likely cause of a blown high voltage fuse, F2, is a failed power tube.

Whenever I get a used amp, I put fresh output tubes in it, just as I would always put fresh strings on a new guitar.

[Chuck H]

And don't jump to conclusions, we could have a speaker/wiring problem instead of the amp itself.

As was said above, all the secondaries are fused. THE most likely cause of a blown high voltage fuse, F2, is a failed power tube.

Whenever I get a used amp, I put fresh output tubes in it, just as I would always put fresh strings on a new guitar.

Truth!!! I had just re-tubed a 1959 Marshall head when I decided to sell it. In my mind it was the right thing to do since I had beaten up the old tubes pretty well. I figure I got an extra $100 because of this and I was able to present receipts. Sure the tubes cost me $120 but the point is that anyone knows you want your new relationship to start out right.

[bartesatan]

I will check the fuses and post on this thread when I have done so.

I found one fuse which was blown, as seen in the two pictures here:
https://ibb.co/0MsqTTK
https://ibb.co/RcMdSMm

It says "F 0,5/250 C" on it. What does the "C" stand for? Does this mean 0.5 amp and 250 volts? I assume the "F" is for fast. Must I get a new fast-blow fuse, or should I consider getting a slow-blow fuse?

Also, could you tell me, is this the f2 fuse?

[DrGonz78]

So yes that is the F2 fuse interrupts the B+ (high voltage) supply if there is a problem. The fuse is 500ma (1/2 amp) 250v fast acting fuse. 3/16" X 3/4" sized fuse.
https://www.amazon.com/Pack-500mA-0-...A5ZPD63TYYGFV5

Just as Enzo had said the power tubes are suspect and could be faulty thus blowing this fuse. Another thing to consider in addition to the power tubes are the 2873 diodes being faulty too. High B+ rectifier diodes (Cr1-Cr4) are also suspects and we can't rule out shorted filter caps.

Do you own or have access to a digital multimeter? You will need to make sure those diodes are not blown as well. At this point we would replace the fuse and pull the power tubes out the next time we fire up the amp. Another recommendation will be to build a light bulb limiter when powering up the amp the first time. The bulb will grow bright if there is excessive current draw and the light bulb limiter will prevent fuses from popping while servicing the amp. When power tubes are removed while powering on it will not be necessary to connect a speaker load to the amp, but if the power tubes are installed you must have a load connected.

Not to take you away from this site but on SSguitar website there is this exact amp and a thread that talks about all of this in great detail. My suggestion is to read this other thread completely and read all links about building a light bulb limiter.
https://www.ssguitar.com/index.php?topic=3589.0

[bartesatan]

Just as Enzo had said the power tubes are suspect and could be faulty thus blowing this fuse

The power tubes that are in it now are two Sylvania 6L6GC STR-387. Do you have any recommendations for new ones?

[Enzo]

Oh, those are nice tubes, too bad if one failed. Most any current production 6L6 should work fine. I always got good service from the Ruby 6L6GCMSTR. never had bad ones, they sounded fine and lasted well. But many of my customers like the 6L6WXT+ Sovteks. There are other good choices.

[Leo_Gnardo]

The power tubes that are in it now are two Sylvania 6L6GC STR-387. Do you have any recommendations for new ones?

What Enzo said ^^^. Ruby's 6L6GC-MSTR were copied from the tough old Sylvania Fender used to install in their amps. I used them quite a lot. Once JJ got their QC in order, I'm a fan of their 6L6's too for nearly a decade now.