Fender Twin Reverb Black face vs Silverface power

[dpacek]

I'm looking at building a Blackface Twin Reverb based on the AB763
and noted that it's official power rating is 85W-RMS while the Silverface
specs indicate 100W-RMS. the PT and OT transformers, main B+ and out sections look identical in the schematics (AB763 v AA769) but the plate voltages look higher on the 63
(460v) vs 69(408v). Where does that extra 15watts come from on the AA769 ?
I'm still going to build the AB763 but always looking for more insight and more power
Thanks

[MWJB]

Firstly forget the schematic voltages, SF twin voltages varied by over 100vdc depending on year. An AB763 is likely to be over 500vdc in reality. Commonly a "BF" Twin Reverb PT will be around 345-0-345VAC and give 460-470vdc on the 6L6 plates. More B+ = more power. Actual voltages vary from mfr to mfr. If you wanted maximum power you might look for a 375-0-375VAC PT that will give around 510vdc on the power tube plates.

[Jazz P Bass]

I think Leo Fender used 105Vac as a benchmark.
CBS decided to use 117Vac.
Right there is an output "power" difference.
And you are not really going to tell the difference between an 85 watt head & a 100 watt head.

[MWJB]

CBS used 120VAC with a 315-0-315VAC secondary, 404vdc on the plates. 350-0-350VAC for the combination biased AC568 whih the schematic shows as having 6V at the cathodes and a plate to cathode voltage of 464vdc.

AB763 doesn't have a wall AC primary specified, but the more critical secondary voltage is 340-0-340VAC, plate voltage @ 460vdc.

...add 10-15% to account for rise in AC wall voltage over the years.

[diagrammatiks]

It's going to vary by tube quad, speaker reflected load, wall voltage, maybe the weather anyway.

for a guitar amp in those days the numbers they give are pretty much meaningless.

you might get anywhere between 80-100 clean with a quad of 6l6s. double that at peak overdrive.

also the blackface schumachers and the later silverface output transformers are different.