My Pig Red-Plated One Time

[Platefire]

My Pignose G40V started loosing volume so I started checking patch cords and coñnections but volume stayed down. Then I looked at the power tubes and seen a red plate. So I immediately shut down.


Latter I turned the amp back on as I wanted to verify which tube it was and was going to swap locations to see if the red plating followed the tube or stayed with the socket.


I couldn't get it to red plate again even after three tries about 15 minuets each. I worked on the amp a couple of months ago and the bias voltage was spot on with the schematic.


The only other things I can think of is the power tube are getting worn/weak or either one of the .022 coupling caps prior to the 6L6's is leaking DC voltage in the grid?


My thoughts is order a new set of JJ 6L6's and watch it close for a while. Any other Ideas?

Platefire

[DummyLoad]

if just one tube red-plate, and if you swapped tubes and the red-plating stopped, i'd be suspicious of a bad socket connection at pin5. are the sockets getting loose/worn? 


--pete

[Platefire]

No, I didn't swap the tubes because I couldn't get it to red plate again after three 15 minuet tries. So I couldn't verify for sure which one it was. The power is back to normal volume/sound again also.


My past Experiance when a tube does this intermittently, it's been the tube. Also on a leaking DC coupling caps, it Red-Plates everytime you turn it on. So, so far I'm inclined to think it's a tube on the verge of failing completely.
 Platefire

[shooter]

+1
the lack-luster volume and intermittent red-plate would lead me to new tubes also, but I would inspect the sockets, i've found a couple '60s amps were inside the cups get a "varnished" layer built up

[Platefire]

Yeah, that's a good idea. Think I will pull the tubes a clean the tube pins and socket with contact cleaner. Thanks, Platefire


BTW- That's what Dummyload was getting at.
Think that's worth a shot

[Platefire]

Those tubes in there are Svetlana's given to me used years ago by a friend. I replaced the stock Chinese tubes that came in it with these. I've always been impressed with their sound
 Kind of hoping they won't be bad. Platefire

[Platefire]

I cleaned the tube socket pin grippers and tube pins. The sockets are gripping the tube pins tightly. I've had it running continually for over an hour now with no red plating so far. The volume is loud and tone is undistorted except when you switch on a dirt box.


My Infrared thermometer is reading 190 degrees right above base on glass and 160 degrees at top of glass. Those readings are pretty consistence for both tubes.


Not sure what happened  night before last but can't seem to get it to repeat the same thing. I want to be able to use it with confidence. So I'm going to check it pretty close for a while. Thanks for your recomendations! Platefire

[DummyLoad]

check solder joints. if it's a PCB, pray it's not a cracked trace. check for bad/cracked solder joints to pads.


--pete

[Platefire]

Just got in a new set of JJ 6L6GC's I'm closely watching burn in. If it now Red-Plates, I will know that the problem is internal and go after it.
Platefire

[Platefire]

Guess what? The new JJ's have been doing fine. So it was those old tubes. Platefire