Tom- Thanks very much. This is the most specific information I have
recieved on the Clipperton and related Amps. It makes me a little
aprehensive, but tells me what to look for, and what to consider for
protection.
Bill-W4BSG
At 07:42 AM 1/24/01 -0500, you wrote:
>
>Hi Bill.
>
>> are a little inconsistent. Can you clarify which amps were operated
>> which way?
>>
>> Bill-W4BSG
>
>
>You can make any Clipperton modified for ten meters oscillate
>quite easily.
>
>Set the band switch to ten meters. Mesh the loading control in and
>tune the plate control near minimum C while the PA is keyed. You
>can watch the parasitic resistors go up in smoke as the PA
>oscillates above 20 MHz and below the six meter band.
>
>Virtually all un-neutralized 572B or 811A amplifier using four tubes
>will oscillate on 20 Mhz or somewhat higher because the tubes
>have excessive feedthrough on upper HF.
>
> There are even cases where two 572B's are unstable. The Yaesu
>FL-2100 is one example. If you remove the load and driver, key the
>FL2100, and rotate the tuning and loading controls it will oscillate
>on frequencies above 14 MHz or so. That is why Svetlana 572B's,
>which require more cut-off bias than other 572B's, will oscillate in a
>FL-2100 when the PA is on standby. The tubes remain in
>conduction, the antenna relay drops, and the input and output are
>"open circuited". The PA takes off at or near the operating
>frequency, and parts get toasted.
>
>Svetlana's patch was to increase cut-off bias, but the core problem
>is really that the PA needs neutralized to compensate for the high
>feedthrough of 572B's.
>
>You'll find, when driven, the plate current dip is not near maximum
>output, and the maximum grid current is not at anode resonance
>either. Both are indicators of uncontrolled feedback at the operating
>frequency. Both clearly show up in the Clipperton and the FL2100
>Yaesu.
>
>Oscillations near the operating frequency are particularly bad,
>because system Q is high at that frequency so the tank can store
>a lot of energy. Opening the loading control up (while running into a
>load like an antenna) loads the tank, and reduces Q and feedback
>in the PA.
>
>
>73, Tom W8JI
>w8ji@contesting.com
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
>
-
Bill Aycock --- Persimmon Hill
Woodville, Alabama, US 35776
(in the N.E. corner of the State)
W4BSG -- Grid EM64vr
baycock@HiWAAY.net
w4bsg@arrl.net
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
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