Bad PT?

[ricach]

For the 6.3VAC heater winding (disconnected from circuit) I'm reading:
Blu1 to Blu2 - 2.9VAC
Blu1 to GND - 8VAC
Blu2 to GND - 1.3VAC


I'm confused. The readings don't make sense to me.

[bbartilson]

For the 6.3VAC heater winding (disconnected from circuit) I'm reading:
Blu1 to Blu2 - 2.9VAC
Blu1 to GND - 8VAC
Blu2 to GND - 1.3VAC


I'm confused. The readings don't make sense to me.

I would agree. They don't make sense to me either. Disconnect power and measure resistance from each of those wires to each of the other windings. They should ALL read as open circuit. If they don't, you likely have winding problems. Certainly an odd failure mode, but not out of the realm of possibility.

Are you absolutely sure of those readings? Like, you used clip leads or alligator clips to the wires, and not just touching the wires with test points?

Best of luck-
Bill

[ricach]

I'm using the clips. I don't have any continuity between the windings - but I also don't have any continuity in the heater winding either. Guess that's a problem alright. Didn't bother to check that since I was getting some voltage readings.

Also, doing the math I see that the PT was underrated. Schematics shows it as 6.3VAC/1.6A. But 2xEL84 plus 3x12AX7 tells me the heaters require more like 2.4Amps.