Bias voltage/ma problem

[Littlewyan]

17mA Idle Screen Current is quite high for EL34s. Normally its about 8/10mA at the most I'd say. Don't rush your readings, I'm going to bed now Will be back on here again tomorrow though.

[loupy31]

396 pin 3
387 pin 4

[Littlewyan]

See that looks a lot better. What was the bias voltage and plate current?

[loupy31]

Bias was -24 and current was 20mA with the trim pot all the way up

BTW I measured the resistance from B+ to the ot at the tubes, B+ = 397v, the resistance was 45.5 and 44.8

[Littlewyan]

The 6V6s are just right biased as they are, idle screen current is good and plate current.

Now going by the OT Winding resistance the EL34s were biased at 155mA!

Your B+ was 397V, Plate voltage was 390V, Winding Resistance 45Ohms - 7V / 45Ohms = 155mA

I'm guessing the EL34 readings were taken when the bias was at -24V?

[loupy31]

Yes -24v, that is correct same as when I measured the 6v6's

[Littlewyan]

Ok put the 150K resistor back in the bias circuit, set the bias to -33V, put the EL34s back in and measure the B+, plate voltage, screen voltage and B+2 voltage again please.