I think you have a bad tube. It may get worse. You should call whoever sold it to you and try to get a new one.
9 responses Add your response
No, they're not supposed to do that. It sounds like some voltage may be arcing across the tube pins at turn on. You might want to look at the underside of the circuit board to see if you can locate the place (burnt spot) where the arcing is taking place. If it were my amp, I'd take it to a tech for service rather than risk damaging the amp. I'd want to take care of this minor problem before it became a major problem down the road.
They shouldn't do that, and it is NOT a minor problem when an amp smokes output tubes in minutes. It went from normal bias to zero volt output, and flashed another tube in the same location. The only possibilities are: very poorly matched tubes, a bad batch of tubes (for example, you may have tubes that were rejected by someone else), incompatibility with GE tubes or an amp malfunction.
I recommend seeing if the amp performs properly with the original tubes; if so, the amp is not at fault, leaving only the tubes as culprits (if it doesn't bias properly, the flashes damaged the amp). I seem to remember that VTL likes to use higher than usual plate voltages, and maybe the GEs cannot handle it. If the RCAs work fine, maybe you should track down some more of them and dump those GEs.
Does your amp delay the B+ at turn on? Tubes, output tubes in particular, can arc if the high voltage is present before the cathode can build up a sufficient space charge of electrons. This can also occur with "weak" or old output tubes that are driven hard. There isn't enough space charge to supply the current needs and cathode stripping can occur; which can lead to arcing.
John: I am not sure if the amp delays the B+ at turn on.
On thing I forgot to mention is that I replace the tube when the amp is slightly warm. Maybe there was a mismatch in temprature between the tube at turn on but I am not sure.
On thing I notice is that the trouble tube does not have a blue glow on its glass surface like the others in the same amp.
I bought those tubes from Ebay so that may explain whay tubes are bad.
Does anyone know of a good place to buy some good RCA 807?
i don't think the VTLs delay the B+. I've smoked a number of fuses due to power surges but the only problem i had with tubes was from a near lightning hit which took out the fueses and one tube. given the fact the tubes were going in the same location i'd vote for an amp problem and not use it until you fix it so you don't follow a potential minor problem with things like trannies.
sounds to me like something is shorting out. the impact of the amp being warm could be that when hot the trouble spot has expanded to cause the short and when cold it doesn't make contact. I had a guitar amp with a bad resistor connection that mad the amp cut out until it warmed up...it finally went totally south. also replacing the tubes a couple of times could have moved the socket enought to maybe seperate the trouble spots. send it in!