amplifier on the fritz question

[Jason01]

My amp powers up fine and sounds fine until its been on for about an hour or so and then starts to hiss and crackle. I tapped on the tubes thinking maybe one of them was going bad but it didn't have any audible effect (one of the power tubes did seem to have a very faint blue glow in the middle). The power tubes are all pretty new, they were replaced when I had the amp shipped to me and the shipper neglected to pull the tubes before shipping (none survived). Any ideas on whats making the hiss? I had the amp checked out when it was retubed so I'm suprised to see this kind of trouble already. When I shut it off for a bit and it has time to cool down the hiss will go away.

[Thundernotes]

What make/model of amp is it?

Typically, a blue glow is fine. It's just the ionization of some residual gasses in the tube. Just make sure the metal parts aren't turning orange.

[Jason01]

VHT pittbull classic 2x12 combo

[Turdus]

sounds tube, or maybe socket, related to me. I would try some non residue contact cleaner in the sockets first. I buy my stuff at an electronics supply store. It's MG Chemical Electrosolve.

Perhaps others here can recco similar product from radio shack, etc.

[tbonesullivan]

get some electrical contact cleaner from radio shack, and some tuner control cleaner and lubricant. use a 1/4 inch plug and put the contact cleaner on it, and work it in and out of the input jack, and every other jack in the amp, putting on more cleaner each time. Then take out the tubes, and take each tube, brush the contact cleaner on the tube pins, and push it in and out of the tube sockets a few times. do this for all of the tubes, including preamp. then take the tubes out and give it an hour to dry.

If you still have issues, it's probably time to take it to a tech. they are definitely worth having a pro look at. It could be a cold solder joint, or some component becoming thermally reactive, or even just dirty spade connectors. But an amp tech with years of experience is definitely preferable.

[JGale]

You didn't let the smoke out did you!?

NEZVEZR let the smoke out of your tubed appliance.

[Jason01]

I have a can of deoxit, I'll give that a try as you suggest tbone and see how that works. I sure hope its something that simple.

[DaveH]

from radio shack, and some tuner control cleaner and lubricant.

I wouldn't use anything with oil in it, at least on tube sockets (with the possible exception of Pro-Gold).

The Deoxit is the best stuff you can get for cleaning pots, switches, and jacks....and you just happen to already have a can on hand! If it's a contaminant issue, this will take care of it.

[carfish7]

With the issue coming and going with use (warming up fully/cooling down), I'd suspect a component level issue. Exhaust all of the common maintenance potentialities first, of course, 'cuz a good tech will go over those points as well in doing any proper servicing.

Good luck!

[Thundernotes]

component-wise, I'd suspect maybe a screen-grid or plate load resistor