Carvin VT50 problem, need help please.

[sjturbo]

My older VT 50 head is in need of some help. When I hit the strings hard I get a buzz/electronic noise,(definitely in the amp). I think this could be a cap issue (which ones?), but then again maybe a tube issue. Can anyone point me in the right direction or suggest some things to try?

[g1]

Plug your guitar into the FX return jack. Is the problem still there or not?
This should be the schematic:
http://music-electronics-forum.com/a...ge50-rev-e.zip

[sjturbo]

Thanks g1! I greatly appreciate the response. That should tell me if the problem is in the preamp or output stage. Should the output of the guitar will be sufficient to drive the output tubes or will I need to put a overdrive pedal before the return? Thanks!

[Jazz P Bass]

Thanks g1! I greatly appreciate the response. That should tell me if the problem is in the preamp or output stage. Should the output of the guitar will be sufficient to drive the output tubes or will I need to put a overdrive pedal before the return? Thanks!

The guitar at full volume will 'drive' the output section.

Maybe not to full power but for this test (preamp or power amp problem) it will suffice.

[sjturbo]

Thanks JPB! And thanks again for the input on the 5e3 mod!

[sjturbo]

Ok, finally got to plug into the FX Return jack and I still have a distorted sound with hard pick attack! So does that sound like caps or tubes? If caps which ones? Thanks again in advance. Your feedback is greatly appreciated!!

[Enzo]

That sounds like we determined it is the power amp with the problem.

Now explore. The drawing has voltages on it, so check them. For instance, are there plate voltages on all the plates? Is ther signal on both plates of the phase inverter? Are all four power tubes running? Ie is there B+ on pin 3 AND 4? Is there reasonable biavoltage on pin 5 of each? Does signal reach pin 5 of each?

[Chuck H]

Just want to add...

Does the guitar being used for the test have a preamp and if yes are we sure the battery is good?

[sjturbo]

No preamp Chuck H. Thanks Enzo,it may be a week before I can tear it down and start checking voltages. BTW some time ago I adjusted the bias up in the low to mid 80's. I can't remember if the problem was there previous to the change though.