Alek,
I'm glad this fixed your amp, and was a blessing in disguise to prove a point
that not all amps of one model are stable. In other words, even though an amp
may be stable, another of the same model may exhibit signs of parasitics, and
act squirelly like this one. There was a test done to prove that no such things
as parasitics existed using 1-2 amps which were stable anyhow. The test did not
use other amps of the same model which shown signs of parasitic action. This
throws that test out the window, and proves the point. I'm sure Rich Measures,
and a few others know of what I speak, and can concur. Even though other
FL-2100B's may be stable, it does not necessarily mean all are (same with any
amp of any model). It also proves that parasitic supressors do in fact work, do
their job, and that nichrome supressors work where standard supressors using
tinned wire may fail due to a lower impedance. I would say your experience
summed it up nicely! Thanks for letting all of us know th
e outcome of your project.
Best,
Will
Amateur Transformer
*********** REPLY SEPARATOR ***********
On 12/7/05 at 5:05 PM Alek Petkovic wrote:
>Thanks to all who offered their assistance regarding the arcing 2100B.
>The
>amp has been stabilised.
>
>Dave, W8NF and Rich, AG6K were instrumental in curing the problem.
>
>I checked the 33 Ohm grid resistors and they were a bit higher than spec.
>They were not the original items. I changed them for some 30 Ohm units and
>added around 1000pF to the existing 200pF grid capacitors.
>
>As well, I made up some Nichrome suppressors from a spare kit I had lying
>around. With these and the grid mods, the amp has become unconditionally
>stable when keyed up with open circuit input and output terminals.
>
>Before, I added the nichrome suppressors, I installed a couple of good
>suppressors from a previously modded 2100Z. With these installed, with the
>grid mods, the amp still produced a purple arc between the plates of the
>loading cap.
>
>I carried out tests for arcing after each step described above. It wasn't
>until all the mods were done that the amp started to behave.
>
>I hasten to point out that the amplifier seemed totally ok before any mods
>were done with a radio on the input and a load on the output. It was only
>by chance that I had the amp on the bench with nothing connected to it.
>
>Other 2100B owners might care to experiment along the same lines with
>their
>amp.
>
>73 All,
>Alek. VK6APK
>
>
>
>http://www.qrz.com/vk6apk
>
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