Peavey Triple X Head Heater (FILA, FILB) Voltage Question

[marcumh]

Wondering if any one knows what the the FILA and FILB voltages are on the Peavey Triple X head? I am measuring ~2.7 - 2.8 volts AC across FILA and FILB but the schematic doesn't seem to specify what the voltages "should" be. Just wanting to make sure that this measurement seems in the ball park.

Thanks,

[Enzo]

Before I look at the schematic, the first thought through my head is this: do the tube heaters light up and look more or less normal? If they do, then the heaters are working and whatever they measure is OK.

FIl A and FIL B are the two leads from the power transformer heater winding. They are wired directly to the heaters of the four power tubes and the phase inverter, all wired in parallel. The schematic doesn't mention a voltage there because it is wired direct to the tubes, so it is understood that it is a 6.3VAC winding.

Now when you report there is 2.8vAC "across" FIL A and FIL B, that should mean between those two wires. Is that what you mean? Or do you mean you get that voltage to ground from each of them? Putting a meter probe on FIL A and one on FIL B we should get 6VAC or so. AC voltage to ground there is meaningless, since there is no ground connection for that winding. However, those 6v heaters should ALSO be riding atop +24vDC. SO 24vDC to ground from either, but 6vAC between them.

Just keep in mind that what matters for a 6L6 tube is having 6VAC from pin 2 to pin 7. The voltage to ground doesn;t matter.

If you genuinely have only 2.8vAC across the heaters, then the tubes would be very dim and the amp would not work well if at all. Most likely cause of such a low voltage would be having the amp switch to 240v mode while plugged into 120VAC mains. Though as far as I know, this model is not switchable.


And just in case, the three preamp tubes are wired in 12v mode, and are in series between +18VDC and -18VDC. That is 36VDC with three 12v tube heaters in series who want 36v.