Rich said;
>However, with an oscilloscope, when I connected the load,
>the output V briefly spiked downward around 50%. When I disconnected the
>load, the output spiked upward about 50%.
I'm not sure if that happens with a tuned choke (I don't like calling it
'resonant' because we've seen it had better not be!) but those spikes are why
you need a good big capacitor on the output to keep the dynamic regulation.
One reason that you can see the technique used in big (5kW and up) commercial
tx's with relatively small capacitors (10 to 20 uF) is that most of those run
ISB type services, frequently with multi channel type teleprinter signals on the
other sideband: this significantly reduces the percentage plate current change
and reduces the significance of the effect.
G2DAF wrote about the problem over 40 years ago, and in the design of the G2DAF
linear (?), he didn't use a smoothing choke. However, he did use 866 rectifiers
with capacitor input, and enough capacity that he was pushing the peak current
ratings of those tubes. Now whether or not that was symptomatic of Dick's
design approach, I leave you to judge.
73
Peter G3RZP
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