Leaking coupling cap question

[labb]

How much DC voltage on the grid can an EL84 stand before it starts to red plate

[sluckey]

That totally depends on the voltage on the cathode. 

[labb]

22 volts for 2 tubes at the cathode bias resistor

[tubeswell]

That totally depends on the voltage on the cathode. 

And partly on the voltage on the screen


 

[tubeswell]

22 volts for 2 tubes at the cathode bias resistor

Seems like overkill.

Is the red plating occurring at idle or under heavy signal conditions?


Or is it merely something you’re worried that might happen?

[sluckey]

22 volts for 2 tubes at the cathode bias resistor

What size cathode resistor? That doesn't sound good. Most likely being driven up by leaky coupling caps. Disconnect the coupling caps and see if the cathode voltage drops. I have several cathode biased EL84 amps and they all run about 10V to 12V on the cathode.

[labb]

Well, just dang it. I finally found what my problem is. I have been building amps for some 25 + years and this is only the second time that I can remember that it has happened. My board is conductive around the high voltage  points. I build with eyelets on 5/16 inch spacings. I am getting DC volts on the grids of the EL84 power tubes. Gave the board a good cleaning and I had flux that I should have cleaned before powering up. Cleaning helped but I still had some voltage around the eyelets for the leads to the tube grids.  The board is suppose to be G10 glass epoxy from Tubedepot. It is the red. The only other time I had this happen was the same board but black. I am old and building is now hard. I was thinking this was to be my last build and now I guess I will have to start over with it. Don't give up. Never give up. Thanks to all that responded. And Steve, If I could give out a reward to those that have helped me through the years yours would be the first and the biggest.

[HotBluePlates]

... My board is conductive ...  The board is suppose to be G10 glass epoxy from Tubedepot. ... The only other time I had this happen was the same board but black. ...

Was that other board also from Tubedepot?

"Conductive" is something that should never happen with a fiberglass G10 board.  It sounds like whatever is used to dye the epoxy is the conductive bit, and other users oughta be warned away from it.

[tdvt]

The board is suppose to be G10 glass epoxy from Tubedepot. It is the red. The only other time I had this happen was the same board but black.

Not good to hear, I think I have a few small pieces of some black G10 board from them.

Is this the 1/8" thick stuff that is conducting?

I ask, as you are using eyelets & I recall them selling thinner stuff at one point (different material...?)