#1
I installed tubes about a year and half ago on my JVM410H. I put them on the hotter side but nothing too radical. Recently
I encountered a Red plated tube after my amps volume suddenly decreased. I`m wondering if the tube is just old, the bias is too hot, or I have some kind of damage that needs to be professionally fixed. I don`t want to spend 200 dollars on new tubes if there is a bigger issue to fix. Also, If a tube red plates, is it garbage at that point or is it worth a shot trying to bring the bias cooler?
Thank You
If it fits it shits
#2
It's probably best to replace tubes when they redplate. Usually not going to be any good. Bias can and does drift over time, so if you biased a little hot it could've been within safe parameters when you set it but drifted too high later. If you feel comfortable with risking another set of tubes you could try setting it a little colder. When you have the amp opened up look for anything obviously out of place, like traces that look burned or anything along those lines that could indicate that the redplated tube took anything else with it when it died.
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#3
Just a single tube is redplating? And you are using matched sets for the output tubes? I would try a colder bias first before replacing tubes. If it is still redplating, try a new set. If that same position redplates again, then you have an issue somewhere else in the circuit.
#4
Quote by Will Lane
Just a single tube is redplating? And you are using matched sets for the output tubes? I would try a colder bias first before replacing tubes. If it is still redplating, try a new set. If that same position redplates again, then you have an issue somewhere else in the circuit.


Will,

I would not personally recommend that. The tube red-plated for a reason. No sense in putting it back in there and taking a chance on it frying something else. There is already a good chance something has fried already. Besides, it happened after a decrease in volume - which would indicate a tube going bad anyway.

So I would lean more toward what RedBaron is saying.

Today's production tubes do not have the longevity of yester-years NOS tubes. It could easily have gone South. Have you seen inside these amps? Not an easy amp to diagnose, trace or otherwise repair. I'd take it to a reputable amp tech. He can look it over and maybe help you salvage some of your other power tubes. You can also try running the amp at half power with just 2 known good power tubes - but I would consult your tech or Marshall before doing that. Also consider running the amp on the cooler side. It will make your picking tighter and tubes will last longer. Lastly, make sure you are buying from a good online tube dealer. If you need help with that - just ask.

Good luck,
#5
thanks guys. I took a closer look. all tubes seemed to have been burned over the months. I dont see any sign of burn underneath thankfully. I'll get a new matched pair bias it on the colder side and see how she does.
If it fits it shits
#6
It should not have been operating under those circumstances for some time. I would get it looked at even prior to New tubes.
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