Metropoulos Forum

Hello all;

I had posted a previous message about higher voltages on a new build using Marstran transformers. Thanks for all those who replied.

The KT66's are in and I am getting 54mV on V4 and 57mV on V5, pin 8. That's with the bias pot fully counter clockwise.

Is that acceptable or would you put in a higher value resistor on the bias pot (68K presently) to get it down? I've got a 150K 1/2 watt and a 100K 1 watt.

Any suggestions?

OK;

My mistake. The plug was not all there way in on my speaker cabinet. So the amp was not getting the proper load.

Now the voltages are adjusted to 43mV on V4, 44mV on V5. That's better.

I'm sure this has been discussed before but what about putting EL34's in there. If so, bias level?

If you are following the typical build instructions, the 70% formula should be therein...
EDIT: I found it... For KT66s: 19 / Your B+ voltage (what is yours?)
e.g. 19 / 450 = .042
If you need to lower the bias more, change the bias feed resistor (the one feeding the diode) downward (what is in there now? 220k? Try 150k). You should not need to mess with the other resistors in the bias circuit.

You should change the screen resistors on the sockets to 1k if you wanna do EL34s...