ShortScale.org

owing to my deville being stuck elsewhere at the moment, i had to use our singer's TSL122...

An hour after being turned on for the first time in about 3 months, things suddenly started to smell of burning - two of the output tubes were glowing red and shortly after that the fuse went... guessing this is a case of blown tubes?

if i replace the fuse and the glowing red EL34's hopefully everything will work fine (seriously, who puts 100w into a 2x12...) but will it need re-biasing afterwards?

On the plus side, it meant having to use the studio's Rockerverb 50, which was lush beyond words...

Were they red-plating? i.e. very obvious red patches?

The bias could be way off or they could be bad tubes, or something else on the TSL could be suspect. Fuses blow for a reason, it could be bad tubes, the bias being messed up or another fault which caused it. It may well just blow again, but new tubes and a fuse would be the first thing to try.

they didn't seem to be doing anything out of the ordinary beforehand, apart from being a bit quieter than normal . then caught a whiff of electrical burning and two of the four power-amp tubes were glowing bright red - first time I've seen anything like this though. Figured that new tubes and fuse would be a reasonable place to start and if it's still not right then check the bias and/or get it serviced.

Sounds like a plan batman

as a rule of thumb is it best to re-bias anyway, after replacing output tubes?

Generally, and particularly in a case like this. You want to make sure everything is within the operating region after you get a fuse blow and tube failure