[Amps] Automatic bandswitching

[Peter Chadwick]

Bill said:
>Anyone remember the National MB-150 all band (except 160 and maybe 
WARC)  network?<
I suspect it would be REAL fun trying to make one to cover all the HF ham bands below 30MHz. A problem is that you can get it to resonate at two frequencies at once, where one is a harmonic of the other. For 5 bands, it  was an 'all right I suppose' compromise, but the L-C ratio could be right only on a few bands (typically 2). But it was convenient.............
Probably the most efficient is plug in coils. I've seen photos of a pre WW2 HF tx that ran 100kW out: it had 'plug in tank circuits' for the PA. Each one was on a wagon running along a narrow gauge railway, and to change band, you pulled out the one, shunted it in a siding, pulled the switch (anglice, 'points') and a pushed another one into place. Hardly a  fast band change. I suppose if you used vapour phase cooled tubes, you could generate some steam to pull the PA tank circuits around....

73

Peter G3RZP