Next question is related in that tank circuits in most commercial amplifiers
use a shorting switch to select the inductance values. Where as, the amp.
circuit designs in ARRL Handbook, etc. use a non shorting switch. Which is
the better (electrical) switch method - shorting or non-shorting?
73,
Mike, K4GMH
This problem really becomes evident when you depart from the 5-band tank circuit
by adding 160 meters and/or WARC band taps. I built several amps from handbook
articles; the last one being an 8877. I used a brand new Radio Switch band
switch which was non-shorting, just as shown in the diagram in the article. I
immediately burned the switch to a crisp! There is a tremendous voltage
build-up in the floating coil section. When the band switch was set to 40
meters, the floating turns for 80 and 160 meters wreaked havoc and all hell
broke loose. I now use band switches that are proven in commercial and amateur
amps and are the shorting type. I have never figured out why the ARRL or the
original builders of the projects in the articles did not have these problems
themselves. When I build an 8877 amp, I use the scheme from an Alpha 77DX and
duplicate the parts, or use similar but beefier ones.
Again, if you are only interested in 80-10 meters in 5 bands, there is probably
not a problem, as long as the band switch rating has some head room for voltage
and current.
(((73)))
Phil, K5PC
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