[Amps] Inductance Variations

[Phil Clements]

> 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