[cathoderay57]

I can't agree with Post #39. A.M. Ball's Radio Valve and Transistor Data lists output valves operating in push-pull. While the data column's title for Rk states (per valve (Ohms)) there is a postscript against the actual value that says "common resistor" which in the case of 6K6 is 400 Ohms. Each valve requires the same grid bias voltage and for a common cathode resistor it will carry 2 valves' worth of current. Therefore for individual cathode biassing for the same grid bias at half the current then twice the resistance is required i.e 800 Ohms.

I agree lower value resistors can be used for the 6K6 grid1 couplers but I suspect it won't make any noticeable increase in sound output.

The output transformer could possibly have been intended for a 3 Ohm speaker and since you are using an 8 Ohm unit you are possibly losing a bit of output power as a result. Whether you can find a decent 3 Ohm speaker with the required power handling at a reasonable price is another issue of course. When you add negative feedback you'll lose a bit more but you still have the other half of the ECC83 to play with.

Cheers, Jerry