Redplating el84

[StrummersOfThunder]

Question for the amp heads

Noticed last night that the lb30 has a red plating el84

When i was inspecting it earlier I did see a charred looking ??grid stop (I think) resistor tho it tested normal so I left it in (100r I think)


Assuming - bad tube
- shorting tube
- bad cap (cathode bias)

Once I can find my tube stash Ill replace that el84 and the resistor.

Anything else I should do ?

[StrummersOfThunder]

[StrummersOfThunder]

[RectifiedAmps]

That looks like a resistor to pin 3, which would make it a cathode bias resistor. Looks like it was working hard to do its job. You don’t have to replace it and since the amp seems to have individual biasing you can just pop in another valve. Just to be safe, I’d try one of the other old valves in there and then put your new valve in a different spot. Have the amp on for a bit and then check for redplating again. Ideally you’d want to measure the voltage across all of those 100r bias resistors, just to make sure there’s nothing else going on except a worn out valve. The voltages should be roughly equal.

[NippleWrestler]

With a burn mark like that I'd replace the resistor at a matter of principle. It'll take 30 seconds. I'd use a vishay 5 watt as well for peace of mind.

Good shout on swapping tubes around to see if the same tube goes wonky in another socket. Hopefully it's a just a bad tube and not something more serious.

[StrummersOfThunder]

That looks like a resistor to pin 3, which would make it a cathode bias resistor. Looks like it was working hard to do its job. You don’t have to replace it and since the amp seems to have individual biasing you can just pop in another valve. Just to be safe, I’d try one of the other old valves in there and then put your new valve in a different spot. Have the amp on for a bit and then check for redplating again. Ideally you’d want to measure the voltage across all of those 100r bias resistors, just to make sure there’s nothing else going on except a worn out valve. The voltages should be roughly equal.

A very good example of me not knowing what I’m talking about

Thanks for the advice and info

[MikeC]

That looks like a resistor to pin 3, which would make it a cathode bias resistor. Looks like it was working hard to do its job. You don’t have to replace it and since the amp seems to have individual biasing you can just pop in another valve. Just to be safe, I’d try one of the other old valves in there and then put your new valve in a different spot. Have the amp on for a bit and then check for redplating again. Ideally you’d want to measure the voltage across all of those 100r bias resistors, just to make sure there’s nothing else going on except a worn out valve. The voltages should be roughly equal.

Strummers, do let us know if it is the valve.

[jeremyb]

Nothing to add but some humour!

[RectifiedAmps]

Nothing to add but some humour!

Built-in ciggie lighter - a useful feature!

[jeremyb]

Nothing to add but some humour!

Built-in ciggie lighter - a useful feature!

Is this how vapes work?!?!??!