G'day Morris.
The method you described is probably more appropriate for setting the
output pi circuit settings.
I don't think you can use that method for the input.
I would have thought that you would be better off leaving the tubes in
situ and leave the resistor out of it and then do the procedure you
described. That should allow you to tune it with all the effects of the
tubes' capacitance/inductance in circuit. Dunno if it would work but it
must surely get you closer than with the resistor.
Good luck and 73,
Alek. VK6APK
On 6/04/2015 9:34 AM, Morris Wideman via Amps wrote:
Hello
I have a old Yaesu FL2000B amp that has been giving me fits and thought I would
see if group has some thoughts that might help out here. I have had this amp
many years and used it with very little problems even though it has always
showed reflected power on the input side. Back when I used a Drake T4X to drive
it no problems with the reflected. I now have a FT1000mp and its built in ant
tuner takes care of the reflected. About 3 months ago one of the tubes shorted
grid to plate and burned up a grid resistor and trashed the electronic bias
circuit I had put in many years ago. I thought this was opportunity to work on
the reflected problem. I fixed the aforementioned problems and I have a pair of
tubes in that put out resonable power now so I beleive the tubes are good. That
leaves only the amps input ckt reflected power to deal with.In my searching I
found a article detailing a method using a resistor to simulate the tubes input
impedance and use something like a MFJ 259B fo
r tuning to match with the amp off. I tried this method and used a external
supply to activate the changeover relay. I was able to change capacitance
values to obtain a very good match on those bands that were bad not all needed
this but those that did turned out very good this way. However when firing up
the amp my new match is now worse than before. The manual for the amp
recommends disconnecting the HV leads from the transformer and tuning the input
I also tried this with the same poor results. Most of my efforts have been
spent on 10M as this is one of the worse bands with at least a 2.1 swr and I
noticed that the plate and load adjustment greatly affects the SWR reading max
out is not the lowest SWR point. I have tested the changeover relay and the
band switch to make sure they are properly making contact and swiching as they
should. I have correct idle current and decent output power.I just need to get
the reflected power down but nothing I have tried seems to work I w
as hoping someone might have a new suggestion.Thanks for your time73 Morris
wa4mit
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From sunny Binningup, Western Australia.
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