[Patrick]

How critical is the primary impedence of the output xfmr? I'm talking specifically about 6V6 push-pull. If the wattage is similar, and the secondary impedence is correct, how much impact will variances in the primary have. The reason I'm asking is, I have a universal push-pull xfmr with variable primary from 1200-25000 Hz, but the schematic shows a 700Ω primary.

[loepke72]

700 ohms sounds more like the DC resistance. The impedance is probably more like 7000-8000 ohms plate-to-plate. It's not overly critical, just don't get too far away from this value.

[Patrick]

700 ohms sounds more like the DC resistance. The impedance is probably more like 7000-8000 ohms plate-to-plate. It's not overly critical, just don't get too far away from this value.

I think I've forgotten everything I use to know. How would I determine the input impedence? Plate voltage is supposed to be 273V, 15W output, 700Ω DC resistance?

[loepke72]

Impedance ratio is the square of the turns ratio, but that might be hard to measure if the transformer is bad. IIRC the load impedance given in the tube manuals for push pull 6V6s is 8000 ohms. Much more than that and power output falls off, much lower and distortion rises and power output falls off as well.

[Patrick]

So generally speaking, 7k-8k would be appropriate with a 6V6 configuration since we're only dealing with occasional AM listening?

[loepke72]

I think it would work just fine.

[Patrick]

Thank you.

[codefox1]

Tubes are not that picky about matches - within limits-. Neither are speakers or ears for that matter.

[Stan the Man]

Will this help??

[Patrick]

Good reference. I'll keep that. Thanks,Stan.