5E3 biasing with Power Scaling

SunDevil

Gents,
 
I have a 5E3 which is power scaled and running a 5V4 rectifier

I have been reading that it might be an idea to go to a higher cathode bias resistor with the rectifier to cool the bias - current value is 270R and the suggestion is to go as high as 390R

With the power scaling engaged, I only get 7.5v pin 8 to ground and a voltage Pin 3-8 of 127v - That gives me a heady 2W dissipation and a plate current of 13mA

If the PS out of the circuit, I get 24v pin 8 to ground and a plate voltage of 356v - 15W and 42mA, which looks a touch high

Now, if I go off the amp at full whack, a 390R cathode bias resistor brings that down to 10W and 29mA
330R would give 12W 35mA
300R would give 14W and 38mA

However, with the scaling is (and how I'm, playing it) that would drop the plate current to 9mA with 390R and 11mA with 330R

So - what to do?

martinw

Bias the amp with the Power Scaling at 100% i.e. fully up.
Forget any other measurements as they're not relevant.

martinw

So choose what you want to Bias the amp to with the amp at 100% PS. I'd go for a 330r based on your figures.

SunDevil

Thanks Martin!