[R-390] Re: R-390 Digest, Vol 25, Issue 10

[Barry]

> Barry,
> Did you experiment with different tubes yet?
> There is only the one adjustment of the cap and not the coil>
> Rich

Yes, I tried different tubes with little or no difference.

I tried something a bit different tonight.  I connected the signal generator
to the control grid of V701.  At a 2.6V peak-to-peak signal, the PTO output
shows a nice strong 8V peak-to-peak signal.  The same signal at the cathode
produced virtually no change on the output.

Is it correct to assume that R701 should be developing an AC voltage across
it of a similar amplitude as the 2.6V signal from the generator (maybe 1.5V
to 2V) in order to get 4V to 6V on the output?  Those are just ballpark
figures, but I'm wondering if the grid voltages I'm getting are insufficient
to drive the output closer to the correct output level?

I tried measuring the signal on the grid, but the 'scope takes the wind out
of the grid circuit's sails and it stops oscillating when I attempt to view
the signal on the 'scope.  I'm seeing -1.7VDC on the grid just as it should
be so I'm wondering what AC voltages should be riding on this.

Thanks,

Barry - N4BUQ