>As I recall, he mentioned that, however, we were discussing bandswitch
>arcing -- like that shown in photographs A and B on page 33 of the Oct.
>1990 *QST* article, "Parasitics Revisited", which is why he called me.
>According to Mr. Paul Pagel, Ameritron customers whose bandswitches
>seemingly had failed quite similarly were telephoning Mr. Rauch and
>asking questions -- which I presumed were somewhat "unfriendly".
However, Rich, I have problems with the concept of VHF oscillations
causing bandswitch damage. The tank circuit rejects VHF signals. So I
fail to see how the VHF voltage could get high enough.
Rather I would guess that the damaged bandswitches are either under-rated
for high power use on HF or (and more likely) that the amplifier in
question is unstable at HF and is potentially oscillating at HF.
I haven't proved this, and I put if forth on the reflector for comment:
Has anyone measured the impedance of the plate RFC at VHF? The reason I
ask is that by the time we get to 100 MHz, the RFC has already gone
through several points of series resonance. With each resonance each
succeeding peak impedance is less and less. So, my unproven hypothesis
is that at 100 MHz the choke could actually look like a low impedance.
Certainly much lower than the impedance of the Tune C. I would expect
any VHF energy then to be shunted to ground via the choke. So blown
chokes I would expect. Blown bandswitches from VHF oscillation is
something I have a real problem with.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@webspun.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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