At 06:15 PM 4/26/97 EDT, you wrote:
>
>That statement only holds true...with reservations....when you are
>dumping into a purely resistive load. Reactances as are typical with some
>ham antennas can transform that voltage to very high levels....if the
>load is not absorbing power the tank voltage can approach that calculated
>in the UNLOADED Q of the circuit...not the magic Q of 12. You were close
>the other day when you mentioned the Tesla Coil effect. The actual
>voltage can vary between both extremes.
As I stated in another thread, this problem is exacerbated when a Pi-L
tank is in use. I would bet the farm that the majority of switch failures
in the SB-1000 occurred when the amp was operating on the lower bands where
the L coil kicks in. However, it is usually a combination of things that
cause failures. Lining the tank coils up parallel to each other in such
a small space was not good engineering practice. Also the two tank coils
are mounted too close to metal, especially the 80/160m coil. A pair of
torriods for this application would have removed the problem and would
have allowed for the same size box to be utilized. Also, Ameritron is now
selling padder caps for tuning and loading that are more robust and do not
drift. A bad padder can cause "Tesla City" very quickly. After suffering
a band switch failure on my SB-1000 in the first few hours of use, I
ordered and installed a kit from Rich Measures. This is not just a new
suppressor mod, but changes the way the anode connects to the plate
blocking cap,and adds a pad in the cathode circuit. This DID cure my
problem!
>Those 2W carbons just do not like VHF heat period.
That is why you see 25 watt globars on commercial amps and my 4-1000A!
(((73)))
Phil, K5PC
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