Current rating of PT

[jon]

I scavenged a set of iron from a Fisher X101-D recently the amp had a slew of 12AX7's and a quad of 7591 (stereo). What do you think the PT is aterd for. I have attached a schem of the power section.

[tubeswell]

I scavenged a set of iron from a Fisher X101-D recently the amp had a slew of 12AX7's and a quad of 7591 (stereo). What do you think the PT is aterd for. I have attached a schem of the power section.

For the heater winding, I'd say (going by 4 x .8A for the 7591s, and the 2 x 12AX7s @ .3A each, and say .5A at the most for the lamp) at least got to be 4.3A, and maybe even 5.5A if the PT also supplied the other (implied 4 x) 12AX7s (based on the 'missing 'V' numbers on the heater supply schematic). In either case its probably a bit more taking into account likelihood of manufacturers conservativeness.

Similarly the HT winding is probably rated at 300-400mA (given 4 x 7591).

Just sayin'

[VacuumVoodoo]

The other 4 AX tubes are heated by combined cathode currents of the 7591 tubes.

[tubeswell]

The other 4 AX tubes are heated by combined cathode currents of the 7591 tubes.

Yes I see now. So he'd be safe to assume the heater winding is probably at least 4.3A (maybe a bit more for a safety margin).

And my guess about the HT winding is probably a bit too high. 4 x 12AX7 heaters in series is 50.4V @.15A. Some of the tube current must be going through the cathode resistor. So possibly 340mA rating on the HT?

[jon]

Geese the pt isn't that big who would have thought!