Mine arrives tomorrow. Will do a pictorial about biasing it at the weekend.
I think it also went on to say that the valves wouldn't run either hot or cold if it were not biased. This implies that I can confidently swap valves without impairing the amp in any way. True? If not, how would biasing help if the valves aren't being over-stressed?
Cheers for the info Kev. Much appreciated.
In the general run of equipment that used valve op stages, radios, tv's, record players etc, the valves were all cathode biased and the other name for this is "autobias".
This meant that a replacement valve "sorted itself out" and no adjustement was necessary or provided. This system worked perfectly because...
1)The valves were operated at their design center values, not max anode wattage and certainly never (IMEXP) above it!
2)Valves had their characteristics tightly controlled and one PLC84 worked bang on anode current for any other, every time, regardless of maker/sample and for years and *&^%ing years!
1)Guitar amp are almost all cathode biased to the limit of anode dissipation (I think most techs would agree?) and some brands/samples will fall out of the loop and "red plate" whilst others will just stay the nice side of destruction. And ...
2) Valves are simply not what they were!
But for those that want to fiddle/experiment fine, for those that know what they are at. For the noob, 10% either way for anode current ain't gonna make much difference if any, to the sound and for FIXED biased amps Ia goes all over the shop with mains volts anyway!
So - definitive answer - if I were to by some replacement valves of the same type (but not necessarily same brand) for my HT20 head, when I came to replace the ones that came in it, would I need to get the amp biased?