werewolf831 said:
This cover had a little spring inside of it. It wouldn't have anything to do with reverb would it? I'd still like to know what this cover is for.
I'm just going to assume that this covered tube is not the phase inverter since it's furthest from the power tubes.
The metal cover's purpose is SCREENING that tube.This is the main issue (because the first tube is the most critical regarding external influences) but such a cover helps as well on reducing microphonics and cooling the tube in question.
If your amp has that "bayonet" shield on the first tube only,that's it....the engineers thought that there's no need to put shields on the others.Still,I'd look at the shape of each small tube's socket:including the first one,do they have the same metal collar around the base?In this case,the amp was initially provided with shields on all smaller tubes,but someone got them off and forget the shields somewhere,except the first tube!
Yes,your assumption is correct:the farthest tube from the outputs is in most cases the input tube (gain).The PI tube is the closest to the outputs,due to a logical signal path.
About the pin cleaning,please DO NOT,for any reason,use something like you said you'd use (contact cleaner) for cleaning!
The point is that this kind of stuff goes for pots,switches or whatever what's supposed to work at ambient temperature.Tube's pins are,thermally,another story....they heat together with the tube and,even if they don't reach the bulb temperature,any of those chemicals used for cleaning will caramelize there.This means a poor contact and more trouble in the future.
You can clean the pins with isopropyl alcohol (the one wich is evaporate fast and doesn't leave any traces of water),the same alcohol we used two decades ago for cleaning the magnetic heads on our beloved reel-tracks.
About bias,yes,it's safe to get the amp to a tech for that operation (it's a must if you changed the output tubes and it should take only a few minutes).
Regards,