tube questions/problems

[Osse]

Hello! I've got an Laney Vh100R amp with 4x 6l6 in the output section.

One of them has gone bad, so i'm about to change them

But when they were alive, two of the output tubes regulary with maybe 15-20 mins interval turned GLOWING RED! I mean, not regularly, but really fucking red, as if the guts of the tube were about to melt down to a pool. while this was going on, for maybe 4-5 minuts maximum, the output of the amp was lowered and an increased noise appeared, then it was going back to normal again.

i thought I had some serious issues with the amp, and contacted swedens most respected tube amp tech, who said this was NORMAL behaivour of an amp.

I mean, why would one of the output tubes go bad if this was not the problem? Anyone else experiencing the same thing with their amp?

I don't want my new SED winged C's go up in smoke... what do ya think?

Thanks

 

[drew_drummer]

Sounds like the bias is too hot. Get your amp professionally rebiased when you replace the tubes. I have the same amp.

 

[Osse]

cool, yeah I've thought about that as the reason...

would be cool to learn to bias it myself, have you ever done it? I've searched but can't find any bias pots on the outside, would I have to open it up?(I'm well aware of the risks...)

Have you tried to change the tubes for El34's?

I've got both, el34 and 6l6 SED winged C's, I don't really know which ones to put in there. Any experiences with both?