>Someone whose name I have lost track of asked:
>
>> >Wonder if anyone can provide some advise regarding band switch arcing on
>> >a FL2100-Z amplifier?
>> >
>> >Twice now the band switch has arced the contacts closed for the 160 and
>> >80 metre positions. Don't know how it happend the first time but the
>> >second time the circumstances were after repairing the switch and tuning
>> >up into a dummy load with very little drive and lots of caution.
>
>Rich opined:
>> At one time, Yaesu factory service said that the problem was due to a
>> VHF parasitic oscillation. For a while, Yaesu had a
>> factory-modification to "fix" the problem. However, it didn't really
>> work and they dropped the mod..
>> IMO, the intermittent bndswitch arcing is VHF parasitic-related. In
>> other FL-2100s, reducing the VHF voltage gain of the 572Bs by installing
>> lower VHF-Rp suppressors appears to have fixed the arcing problem. See
>> 'Parasitics Revisited' in the 9/90 and 10/90 issues of QST magazine for
>> more info.
>
>Rich may well be right, but I will hazard a guess that the arcing has
>nothing at all to do with parasitics, but rather with the timing of the
>antenna change-over relay. .........snip......
There is an easy way to find out. Measure the R of the VHF parasitic
suppressor resistor, Rs, by unsoldering one end from the parallel
inductor. If the resistance of Rs has increased by a substantial amount,
I would suspect a VHF parasitic oscillation. If the resistance is not
far from the tolerance spec, a parasitic was probably NOT the culprit.
note---It is better to tune up an amplifier with full drive since the
tank is designed to operate with full anode current. When drive is
reduced, the anode current is too low and the resultant E/I ratio is
wrong for the tank's design, which results in a mistune. .
Rich---
R. L. Measures, 805-386-3734, AG6K
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