Darling heater voltage

[JVINCENT]

I built a Darling amp using TMcNally's schematic. It sound great, but I measure 13.8 volts on the heaters. Is that too high?

[TomMcNally]

Is that with the tubes in the sockets ?
I have been getting right around 12 volts on mine.

... tom

[Sal Brisindi]

I was getting about 13.8 volts on the heaters on my 2 Darling also and I was going to mention it here. I used a 1 ohm 10 watt resistor in series with coming out of the voltage doubler, I was thinking of upping the value a bit to bring the voltage down.

Sal Brisindi

[EWBrown]

A filament voltage of +/- 10% is OK, the tolerance is worked into most tubes, as a part of normal operation.

I found what with the "269" power transformer, which has a 115VAC rated primary, that the filament and B+ voltages run around 8% to 10% higher as compared to the more expensive "369" power trannie, which has a "true" 120VAC primary option (along with 220 and 240VAC connection) , that the plate and filament voltages run closer to those specified.

IIRC (without looking it up) the two 1626s and one 12SL7 filament consume around 650 mA @ 12.6VDC, so to reduce the filament voltage would take around 1.5 ohms per volt. The "easy way" is to leave the original 1 ohm resistor in place, and then insert another 1 ohm, 5W WW resistor in the other / negative side of the 12.6 VDC circuit.

HTH

/ed B in NH

[JVINCENT]

Thanks for the help. I have a 269EX and 128v ac out of the wall. With the addition of 1ohm on the ground leg, the heaters are at 13.2 v dc. I figure 3 ohms total should be about right.