Ampeg VT-22 noise

[Leo_Gnardo]

After I grounded g3, the whooshing noise is gone. But I don't know if its because I replaced the 600v cap, cleaned all pins and sockets or what. Also, the hum is greatly reduced.

I think I'm going to tackle the bias circuit next. Something seems to be amiss, in order for it to burn out tubes like it did. I will also install a bias pot, probably 50k, once I figure out what's going on.

You should measure your bias current, using shunt method, if you can, or dare... well you can use clip wires to your ammeter so you're not poking around inside while the high voltage is on.

One lead goes to the output transformer center tap, and the other to one plate connection. As long as your meter's internal resistance is low compared to the OT's winding, you'll get a reading that's within a couple percent accuracy, close enough for rock and roll. For milliamps per tube, remember to divide the reading you get by 2 because that current is shared by the pair of tubes on one side of the push pull pair. Then measure the current on the other pair. If you get a figure between 50 to 80 milliamps per PAIR (25 to 40 mA per tube), you're in the right ball park. If it's beyond that, better have a go at that bias supply.

Something else to do - not a bad idea to install fresh bias supply filter cap now it's @ 40 years old.

[AL]

I usually have a standard "fix it" plan when working in the V-Series Ampegs. It's likely overkill but it gives me a little more peace of mind if I'm going to be playing the amp out.

Check (and usually replace) the plate resistors on the power tubes. They go sometimes. I have a VT22 with a chunk blown out of the board because of one of those resistors.

Usually end up rebuilding most of, or all of, the bias supply. There's a .047/600V(??) capacitor at the beginning of the bias supply (before the diode). It always gets replaced.

Visually inspect the rest of the components for heat. Sometimes they read OK but look a little charred. Not worth it for me - I just replace them.

Cap job. Of course. There is plenty of room inside the amp for separate caps on turret strips. I usually just leave in the multi-caps, bend the tabs down and cover with silicone. The mult-cap on the far end by itself gets replaced with a 50/50 multi-cap and a single 47.

Here's a page showing the circuit re-done with individual caps.

http://www.geocities.ws/flintstudio/Re- ... g_Amp.html

Those amps will run 6L6's with no mods. You may want to check a few things if you're going to run EL34's or 6550's.

http://www.triodeel.com/7027.htm

Good luck. And hire a roadie. Those things way a ton.

AL