russian 6p14p red plating

[RussianBear]

Just recieved a pair of 6p14p's from tubetramp yesterday and one of them red plated after a few minutes in my GDS 18watt trem. They were replacing JJ's which have been working fine in this amp. I've searched and it sounds like this has happended to others with these 6p14p's. I'm not home right now to look at the cathode resistor value in my amp but is this where I need to concentrate to solve this problem? (i built my amp from Graydon's kit so I'm not sure what value he usually uses). What numbers should I check for as far as voltage that might indicate a problem?

(i'm a little rusty on my amp tweaking skills....spend most of time playing vs. working on my amps so I'm pretty technically challenged compared to most here.....so thanks in advance for any light you could shed on this for me!)

Kyle

[PepeJara]

What value is your screen resistor?

[Brewmaster]

IIRC correctly GDS kits have a 125 OHm Cathode resistor. I would bump that up to a 150 ohm and odds are that will stop the red plating. Your power tubes will be happier and last longer with the 150 OHm.
Some have bumped the cathode resistor up to 180 to get the voltages where they wanted them.

Post your voltages then watch the avalanche of responses you get to get them under control if that is the issue and not a bad tube.

[StarGeezers]

Wiki says : "when used at its plate rating of 300 volts maximum, " you might check that too ..

[Brewmaster]

I and others have run these with 340v on the plates for close to a year with no issues. Sometimes you just get a bad tube.

[StarGeezers]

Brew, Thanks , that's good to know ... !!! guess being bumped around for thousands of miles and our PO doesn't help a bit ...

[jaysg]

Just recieved a pair of 6p14p's from tubetramp yesterday and one of them red plated after a few minutes in my GDS 18watt trem.

Tell him.