tube changes color

[94Tremoverb]

It's definitely safe in 50W mode - with a (very) few exceptions due to plate voltage rise it's always safe to run a fixed-bias amp with less power tubes than it normally uses - but I'm not sure about 5W since it's cathode-biased.

If one tube is getting much hotter than the other in 50W mode and it's the socket not the tube, something is wrong - either the hot socket has lost its correct bias so it's running far too hot, reasons for this can be a bad grid resistor or coupling cap, and would explain unusually strong blue glow; or the cold socket is not passing current, usually because the screen resistor has failed, which would explain no usual blue glow.

 

[fluff191]

All of my 6L6's look just like that in my Recto. Totally normal.

 

[Waspination]

Interesting. I just saw one of my power tubes look like this in my Express 5:50 the other day. What is weird is that if I switch the left/right tubes, the purple color stays with the socket, not the tube. So is some weird current going on here?

I tried this with mine, and the glowing one was in the same tube. SO its just my tube then which relieves me.

 

[THTH]

This happened to a GE 6550A I had in my JMP. The other tube was fine. These tubes were also really worn from gigging and rehearsals, a 50W Marshall dimed almost 2 years, 4 days a week. Great tubes while they lasted. Sparks and smoke when it went.

 

[fluff191]

Here's the result of my first time trying to Bias my my Recto on my own!!