on 3/5/00 11:14 AM, Terry Gaiser - W6RU at w6ru@lightspeed.net wrote:
> The amplifier was in STANDBY ..... NOT KEYED .... but with all voltages ON !
> I had a reason to remove the top cover (high voltage interlock removed), I
> slowly raised the cover from the front of the amplifier leaving the rear of
> the cover sitting on the amplifier ... when I got the front of the cover
> raised about 3 inches ... all of a sudden the amp made this huge big grunt
> and the circuit breaker tripped off. After I removed the top cover and
> turned the amp back on I had idling plate current in the standby mode. Long
> story short ... I had one of the two 3-500Z's with a grid to filament short
> and that tube had metal particles rolling around inside of it. Ten minutes
> earlier this amp was putting out 1300 watts on 20 meters. NOT knowing what
> had happened I replaced the bad tube and tried again. Guess what ... with
> the cover about 3 inches raised ... yes ... I lost another 3-500Z ! This was
> a damn expensive way of being introduced to the type of oscillation that Mr.
> Denial says can't happen !
Terry,
What happened is that you changed something in your circuit. Yes! The
cabinet of the amp is part of the circuit. Some sort of resonance was
created by lifting the cover and hence your oscillation. But the boundary
conditions of the problem were changed. So you can't say that Tom's claim
is wrong. Those tubes would not have experienced oscillation had you left
the cover down. But having them keyed and moving the cover caused things to
change inside and BOOM!
It was not a static state that caused your oscillations.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
Member: ARRL, AMSAT, DXCC, NRA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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