PART 2: my in-house assumptions & conclusions:
Without being an expert, I assume from the toroidal power supply transformer specs posted above that it can supply up to a max of 7 Amp. current. This seeems to be the current drawn by the output tubes.
Correct me if I'm wrong, but as far as I understood, in push-pull operation, one tube's grid is driven until its plate current cuts off (stops) completely, then the other tube takes over and handles the power output.
If this is correct, and assuming the amp work with 2 pairs of output tube (2 per channel), I assumed that thefilament current in each channel is NOT the sum of the filament current of each of the tubes in this channel (since they actually don't work in paralel but in a sequential way).
Again, if my assumption is correct, it would mean that the TOTAl filament current requirement (drawn from the toroidal power supply transformer) would be:
- for a KT88 quad: 2 x 1,6 = 3,2 Amp
- for a KT120 quad: minimum of 2 x 1,7 = 3,4 Amp - maximum of 2 x 1,95 = 3,9 Amp.
Which in that case would mean that the current requirements are well below the 7 Amp that the toroidal transformer can supply without being overdriven.
Of course, if my assumption is not valid, it would mean that twice the current is needed: 4xKT88 require 6,4 Amp and 4xKT120 require between 6,8 and 7,8 Amp. This would be OK for KT88 when compared to the 7 Amp given by the transformer, but it would be risky (if not impossible) for the KT120.
However, this would go "against" the claim from the manufacturer stating that both the input and output transformers are over-dimensioned for 100 W (twice the power output of the amplifier).
This can lead to think that my assumption was correct, since the range of current required (from 3,2 to 3,9 Amp depending on the case) is approx. 50% of the potential current delivery (7 Amp) by the input transformer....
....
........
............ :-)
To be continued.............