At 11:14 AM 4/27/97 -0400, you wrote:
>
>The SB-1000 band switch, when properly installed, will handle normal
>operating voltages. Unfortunately several things went wrong in the
>SB1000. Heath decided to NOT install an anti-corona washer. That reduced
>the voltage breakdown.
I built one of the last SB-1000 kits. It DID specify the installation
of the washer on the switch contact. It sticks in my mind so well because
I had never seen this done before, and Heath did not explain what function
it had.
>
>None of this stuff is magic or rocket science. It's all common sense and
>normal engineering, and can be verified by traditional math. I've
>measured PA's producing over ten times the normal operating voltage in
>the tank during load faults.
>
I have burned up several band switches on a 10-160m Pi-L by not having
multi-fingered rotors on the band switch to short out coil turns up line
from the band in use, as the Ameritron AL-1500 and Alpha 77D/SX et al do.
The arc has nothing to do with load faults, it is strictly due to the
"apparent "Tesla effect" in the tank. Removing the 160m coil and the
L coil, and reverting back to a Pi network cures the problem, and the
same exact band switch can be used with no glitches, even with severe
miss-tuning. As I stated in an earlier thread, in a Pi network it makes
little difference whether you short unused turns or not, but it is
mandatory in a Pi-L, especially with a 160m coil hanging out there!
Unfortunately, amp projects described in the "Radio Handbook" and the
"ARRL Handbook" lead one to believe a simple "1 arm rotor" band switch
will work in all cases. The "experts" who edit these projects let these
potentially expensive errors proliferate.
Certainly, a load fault (too lightly loaded, antenna/feed line open/shorted,
padder capacitor failure/drift, etc.) will crater almost any circuit.
(((73)))
Phil, K5PC
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