SF Champ problem...

[bluzmn]

I've been working on a SF Champ. When I got it, it only had a 12ax7 in it, so I added a 5y3 and a 6v6 and turned it on. It came on with a loud obnoxious hum for a few seconds and then blew the fuse. I replaced the cap can, hooked the amp up to the variac, and started raising the voltage 10 volts every 10 minutes. At 30 volts, I started hearing intermittent crunchy sounds. I remembered then that the 6v6 tube socket was scorched at pin 3, so I jiggled the 6v6 and then the sounds happened in synch with the jiggling. A guy at an electronics store suggested that I try cleaning the scorching with gunpowder solvent and contact cleaner. I did that, then hooked up the variac again; I got up to 100 volts then the sounds started up again, this time consistently, one after the other. I have a new tube socket now, but I'm worried that if I install it, it will get scorched if there is an underlying problem. Do any of you know what could've caused that kind of damage to the socket? I did find, rattling around in the chassis, the plastic post from the bottom of a tube that has the rib down the side that fits in the notch in the socket so that the right pins go in the right holes. Could this damage have been the result of the wrong pins going in the wrong holes?
Thanks for all your help.

[Gibsonman63]

If I had to guess, the last power tube in the amp before you got it shorted out. They do that sometimes and can leave the carbon trace on the socket when they do. I would check the plate resistor on top of the power tube socket. Sometimes they crackle if they get cooked. I usually put a 2W metal film there because they handle the heat better. Also, change out the cathode bypass capacitors because they are electrolytic and probably beyond thier life expectancy. You may want to chopstick around and see what you find as well.

[Mr.Maggoo]

I had a similar thing happen with a Marshall head. I can't remember which tube it was, but the socket was scorched and, guess what? Now the scorching is a conductor. You are right to replace the socket and the fact that the tube "key" was floating around inside tells me that someone might have installed a tube incorrectly and blew up the socket (and tube). Or a little critter got in there, and got got fried when the amp powered up and burnt up the socket - less likely, but possible.

regardless, the scorched up socket does conduct electricity to the wrong places.

[booj]

I'm thinking the 6V6 doesn't have a plate resistor, but is connected to the output transformer. I'd change the socket and try it again. Also change the bypass capacitor connected to pin 8. Check the value of the cathode resistor connected to pin 8.