EL84 Plate Voltage

[grandmasterflash213]

Hi ive got a SE 5w amp using a 12ax7 and an EL84. It has always had rather harsh quite unpleasant overdrive with power valve OD, im playing around with the plate voltage. Am i right in thinking lowering the plate voltage of the el84 will smooth out the overdrive?
The original reading from ground to pin 7 of el84 (this is plate voltage right?)
was around 330v.

Ive managed to get this to around 270v and the od is now a bit smoother.
I read on ampmaker on setting up the 5w SE amp (similar to mine) that it should be 245v

cheers

[Wakculloch]

I can't see that lowering HT by itself will cause smoother distortion. If however the cathode bias resistor is large, to prevent excessive anode dissipation, then you may be experiencing assymetrical clipping.
From the Mullard and GEC data sheets, they call for a HT of 250V, and a cathode bias resistor of between 140-170R.
Can you give the value of this resistor and the volt drop across it when working at 330V?

[loudthud]

The EL84 is a harsh sounding tube to begin with. There should be a resistor in series with the screen grid. Try increasing it's value to something like 2.2K 2W to 4.7K 2W.

[grandmasterflash213]

Cheers for the help, ill get my multimeter out and check all the voltages, the dissipation should be about 10W right?

thanks

[grandmasterflash213]

ok i had a look at the cathode resistor and it was far too large, there was was 270R in there. I put in a 180R (nearest i had) and it seems to have done the trick. The amp is a lot sweeter sounding when it breaks up, having a nice crunch and chime to it.

I now have:

cathode voltage 6.66 V
B+ 255 V

gives cathode current of 37 mA

dissipation approx. 9.186 W

I suppose this could still do with being a bit higher.

cheers for help!