[Herald1360]

Signal wise all the grids of each half of the output stage are in parallel, so if all the valves were identical, the grids could simply be paralleled up. Unfortunately..... there is a need at least to have some means of balancing up standing currents- hence the variation in separating grid bias from signal feed arrangements. There is also added complication with stopper (series) resistors in various grid circuits to try to stop the whole shebang from taking off.


Back in the days, I suspect it was easier to get reliable high power audio using bigger valves from the RF world than multiple pairs of smallish audio valves.


Also for large audio installations like cinemas etc you could get at least 10dB more bang for your amplifier buck by using horn loaded rather than direct radiator loudspeakers. I suspect that very rarely was more than a few hundred watts of electrical audio required for anything.