On Mar 9, 11:52�pm, Jack Schmidling wrote:
wrote:
One concern I have is that the 15 watt amp will see a load of varying
impedance from the 813 grids. If you are running them Class AB, their
input Z is near infinite until
grid current flows. That reflects back to the 15W amp, which may or
may not affect it.

There is some idling grid current flowing.. about 30 ma if that helps
any. *This is a zero bias set up with screens and grids tied together.

Then you don't need the resistor I mentioned.

I suggest putting a resistor across the secondary of the driver
transformer, so the amp always sees a load. The resistor then sets the
impedance of the transformer.

Someone else suggested a resistor in series but I forgot why. *Are you
addressing the same problem?

No. I was suggesting a resistor across the transformer secondary -
from grid to grid. But since your setup is zero-bias Class B, my
concerns don't apply. The 813 grid/screen connection you are using
provides a load
for the driver.

I think the series-resistor idea meant a small (~100 ohm)
noninductive resistor in series with each grid lead, installed right
at each 813 socket, in case of instability. You obviously don't have
that problem.

One request for your website: MORE PICTURES!

Thanks but I have been doing a Photo of the Week this for 12 years and
that's about 624 to date. *If you just want to fall asleep watching
them, try the slide show.

They're GREAT!

...that 8000 is just beautiful, btw...

Very satisfying to turn a bookend into the heart of a real transmitter.

Yep, I know the feeling.

73 de Jim, N2EY