I just got an interesting email from a Champ builder. His amp was up and running normally when he changed tubes and accidentally installed another 6V6 into the rectifier socket. The amazing thing is the amp functioned but max volume was very much lower than normal. I'm amazed that the 6V6 worked as a rectifier but his functioning Champ proves that it can happen. With a 6V6 in the rectifier socket you would have half the 5v heater voltage connected to a 6V6 heater filament (pin 2). The other 5v heater wire would be connected to the 6V6 cathode (I don't understand how the heaters worked at all). The screen grid would be connected to one of the high voltage AC wires (the other wire would be connected to 6V6 pin 6 no connection). The 6V6 cathode would be connected to the B+ wire (which is normal). So you'd have low filament heat and the screen pulling electrons from the cathode. I'm shocked the screen grid didn't melt from the relatively high current pulled through it but the amp ran like that for a few minutes until he noticed the low max volume.