6V6 problems
Hey! Skip hope you can shed some light on this for me or at least send me in a good direction, here goes!
I have a Eastern Amp (can't find allot of info on it but that doesn't matter) Looks like a old Masco-map 105 cabinet but I digress, for this discussion it is a Class A, single ended amp using tubes 6SL7, 6V6GT, 6X5
Inside it looked like someones home brew project with the rats nest wire job and long leads left to clip other componets onto and stuff like that, however it worked and other than weird tone and vol control interaction it was fine. I was cleaning up the mess and turning the unit on and off as I fixed one thing or another or tried a diffeent value cap, but minor stuff.
Problem begins when I turn it on and pin 3 on 6V6 plate starts arching after checking, the voltage on pin3 comes up and starts to settle in to 325 approx and then ramps up over 500vdc (this is when I shut it down and it starts to arch again).
If I disconnect the grid lead pin 5 it will turn on the plate voltage is a little higher than if it was conducting say 350vdc or so but no arching.
I have gone over all pins and connections to eliminate any stray wire or mistakes, I cleaned and tighted all pins in socket, I've tried different size cathode resistors 250,330,660. Ive tried 2 different size load resistors on grid pin 5 470k and 270k. I've tried 2 different new tubes, Prior to problem it's cathode current was about 45ma.
Hope this is enough that you might point me somewhere, I'll keep working on it!! Thanks in advance for any help!
Yea! I know it's near impossible to tell much when you can't see it but I appreciate the direction. I was just hoping maybe this was something common, I did as you had mentioned and addressed the issue of possible bad plate connection and that took care of my arching however I still have other problems in the preamp so I'll drop back and punt.
But I would love to know if you have ever heard of this amp before so far I have'nt seen another like it, as I mentioned before it looks like a Masco from a distance in shape and style.
It's a Eastern Amplifier Model G.1A s/n 7618 Made in USA
Thanks again for taking your time on this!!
Well, that is a tough one without being able to see the amp, but here are some ideas:
1- Check the voltage at pin 5. It should be zero or slightly negative.
2- Examine the socket itself for any sign of arcing. Arcing can create a carbon path between pins.
3- It could be the output transformer.
4- It could be none of the above. I've been troubleshooting old amps for 25 years, but I can't be sure of the problem without seeing the amp.
Skip Simmons
Skip Simmons Amp Repair