Originally posted by SLY
...(considering that the three of them are 6L6)...

Huh? :confused:

The output tubes in a push-pull circuit are arranged in pairs! I'm not very familiar with Fender amps, and I can't find my book of schematics just now, but I'm pretty sure you should have 2 of those 6L6 tubes, for about 40 Watts output.

There should be a bit of an orange glow from the heater filament, deeep inside the tube. Usually, you can only see it at the very top or bottom of the tube. The whole metal structure should [u]not[/u] be glowing!

The bias adjustment is usually a negative DC voltage applied to the screen grid G2. Some amps have a handy adjustable trimpot, but quite often the stock setup has fixed-value resistors in a voltage-divider string at the output of the bias supply.

Metal sleeves are sometimes placed over the preamp tubes to shield them from electrical noise. That's a good thing to see.