Tube related tantrum

[ricky22]

hey guys hope you can stop me from going insane and stop me pulling my hair out, i usually hang out on the bass section but do like to strum the 6 string from time to time.
My main amp is a Laney VC30. Up until recently all has been fine, love the sound, understand how much my sound improved with valves and that familiar combination of 3 12AX7's and 4 EL84's.
Then suddenly at a recording session all went quiet, my output all but died. On the clean channel things were very quiet unless i turned the gain right up, which made it become very overdriven but still quiet. on the overdrive channel the overdrive worked fine, but once again all was quiet.
After trouble shooting i worked out that all this meant the pre amp tubes all seemed fine. this meant it was probably the power tubes.
Well i have got some new ones, but money is very tight and i have spent all i can now spend, and have them fitted and the problem is still there, just as it was.
SO can you help me work out what is wrong. Nothing looks burnt out on the circuit board and i would have thought there would be no output at all if the output transformer had gone.
Everything seems to be glowing fine and working, hope you guys can spread some light on things

james

[winston]

Unfortunately based on your description it could be a number of things that are wrong with your amp James.

Did you check your preamp stage or final stage valves (tubes) on a valve (tube) tester?

I don't know your particular amp so generally speaking if they check out then it could be something as simple as a master volume or volume pot that has gone bad. Check your speaker connections too. It also might be a transformer that has failed not to mention some other potential issues in the circuit board itself.

[paologregorio]

Check the simplest thing first; the vibrato died on my Fender Twin and it turned out that the problem was one othe 12AX7s in the vibrato section. Once replaced the familiar whacka-whacka of the vibrato worked flawlessly.

[whojamfan]

I had something like that happen with an amp that turned out to be the grid resistors on my power tubes, which eventualy killed the tube and left me in "no sound" land. Troubleshoot the best you can, but do NOT open up the amp and start dinking with things other than replacing tubes. If you don't know what you are doing, even an unplugged amp can kill you!

If this doesn't fix your problem, find the best place locally to do the repair, or even a Laney authorized service center. You don't want some hobbyist with very little experience trying to fix your amp, as more problems than solutions can be created. Good luck, and let us know what happens

[fuzzysi]

I recently went through my guitarists Fender Deville for a similar problem and after going through all the common troubleshooting on Devilles and finding nothing, I cured it by sweating any solder joints that looked even slightly suspect and infact many that looked fine. I didnt realy *do* anything, but it fixed it.

You must bias your new tubes or you could cook them quite quickly. Theres a reasonable chance the bias will be close enough, but if a grid resitor has died or there is a problem in that part of the amp they will most likely cook.

Try to find the schematics for it, then you can see whats doing what, where and why and then check values of components etc.

The main safety issue in tube amps is properly discharging the capacitors. Its not hard, but must be done correctly. You'll find some good info here.
http://studentweb.eku.edu/justin_holton/caps.html

As ever though when poking around tube amps, if in doubt, infact, if not 100% sure of what you are doing and why, don't.

Simon

[whojamfan]

Great link and advice Simon, and welcome to the forum