Tubes red plating

[stacey]

Just wondering if anyone else is having issues with tubes not lasting as long as they use to? I've got a jcm 2000 dsl 100 watt but before anyone goes down the bias drift road it's got a replacement board which I've tested for any issues & all ok. I did replace bias pots about 2 years ago as one was faulty. I usually replace power tubes yearly as I play a fair bit & today the set that are about 2 months old red plated. 2 tubes on one side. Electro harmonix el34s. I usually bias to 66 mv each side.

 

[Chris-in-LA]

I don’t play all my amps all the time but they never red-plate. I did recently buy an 86 2204 that had a leaking coupling cap on the PI, that caused one side to red-plate when I first ran it. But, no problem with any power tubes for years.

 

[Dogs of Doom]

what do you bias it to?

 

[Seanxk]

Red plating is not an indication of old age, it's a sign that your bias is wrong or I suspect something else, perhaps a replaced bias board didn't catch all the damaged components ?.

 

[stacey]

what do you bias it to?

66 mv each side

 

[stacey]

Red plating is not an indication of old age, it's a sign that your bias is wrong or I suspect something else, perhaps a replaced bias board didn't catch all the damaged components ?.

Its a replacement mother board /main board. It did have a faulty bias pot so I replaced both. It's been running solid problem free for 2 years so I'm at a loss as to what can be wrong

 

[Tatzmann]

Which ones V5 and V6 or V7 and V8?

Probably V5 and V6 right?

How many millivolts are measurable
at the pins right now?

 

[stacey]

Which ones V5 and V6 or V7 and V8?

Probably V5 and V6 right?

How many millivolts are measurable
at the pins right now?

V5 & v6 I've put an old set of Svetlanas in & bias to 66mv & all seems OK for the moment.

 

[South Park]

The amp is working so start of with just Turn down the bias one or two volts and see if that helps