Re: Why Does The Output Tube On My Vibro Champ Not Stay Lit?
I'm thinking wrong here. It's not the voltage, it's the current through that resistor. Still applies though in terms of using a higher wattage resistor. A lower voltage rated cap should still be fine. I think they are typically 25 volt caps in the schematics. Of course, the only negative to going with a higher voltage rated cap is size. But you shouldn't really have to go to a high voltage rated cap.
I'm running the hell out of the 6V6 in a SE amp. It's not a champ, but similar, based off an old Valco. There are two cathode bias resistors, switchable. One runs the tube at about 12 watts plate dissipation, the other runs it hot, hot, hot. Over 20 watts plate dissipation. It's not like a clean and dirty set up. It's more like a "normal" and nasty set-up. I didn't build the amp but I've tweaked it. I upgraded the OT and added a choke. It hummed like a SOB and I've got it so quiet with re-working some grounds and wiring, plus adding the choke, that it really shocked me (how relatively quiet it runs). At any rate, the 6V6 plate voltage is over 400 volts at 12 watt dissipation and around 370 volts at 20 watts dissipation. I haven't burnt through a 6V6 yet but they probably wont last very long. It's an interesting amp, it uses a 6SL7 as the driver/preamp tube rather than a 12ax7. Also has a rotary switch that switches the plate resistor and cathode resistor+bypass cap values on the 6SL7 which effectively changes that tubes bias. A couple positions of the switch are close to original spec values. A couple others essentially starve the plate, which makes for some nasty, but interesting tones. There was no bypass cap across the cathode bias resistor on the 6V6. I added one on a switch to switch it in or out. I have a small supply of NOS 6v6's for that amp. I think that there is one current production 6V6 that would probably survive the circuit but I don't think I'd trust current production tubes in general. At any rate, the tube is running outside of it's comfort zone. By a mile, some would argue. Although, I've seen plenty of reports from people with old Champs that claim that the 6V6 is running at 18 (or more) watts plate dissipation with relatively high plate voltages (probably because of more voltage at the wall these days). Overall point being that the 6V6 is a pretty tough tube. At least the old ones were. I get no red-plating. The trannies never get beyond just warm.
At any rate, it sounds like you are on your way to getting it back up and running. I wish I was more of a techie so I could be of greater help but I'm happy to be able to help even if it's just a little bit. Keep updating. I'm curious as to how it will all work out.
