SNIPPED
>There appear to be conflicting observations about a lot of things
>here.
>
>Let me put it to the group. If anybody is interested in having this
>subject put to a real test - not an argument, but a genuine
>experiement,
>derived through proper DOE (Design Of Experiement) procedures, would
>the
>interested parties ante up?
AMEN Arlen! Count me in.
I've an acquaintence who's very good at
>DOE, and I'd be willing to un-modify my SB-220 (which I haven't used
>in
>the ten years since my license expired, so the tubes are old) and
>donate
>it to the cause.
I have several SB-220's here as part of my business. Also a fair amount
of HP test equipment.
Write up a test procedure and I will be very happy to do what I can.
The participants who have theories to prove would
>have
>to state the theories in a methodical manner, i.e.: First, this
>happens,
>then this happens, and then that happens. The DOE experimenter would
>outfit the SB-220 with appropriate measurement apparatus to catch
>these
>brief events when they happen.
I do not think that a methodical approach will work very well...at least
with the SB-220. I have tried numerous times over the past few years to
recreate "events". The gas arc is not prone to programing IMO, once it
happens there is no telling when or if it will happen again.
A true parasitic "should not" occur if the suppressor is undamaged so it
would require some component manipulation to make the amp more readily
unstable.
I have NEVER been able to recreate a tank circuit instability when
connected to a pure dummy load in an SB-220 with perfect tune cap plates
and bandswitch. If either has been previously arced then, yes, I
sometimes can force a component arc..NOT a tube arc!
I will follow your lead Arlen, but I have a gut feeling that we will have
to modify the 220 a bit first...if we want to have enough meaningful data
before the millenium.
In the 220 adding a fixed 10pf C across the Tune cap would require
modifying the tank coil, the C is already just about full open on 10 as
it is. I doubt if the Tune cap is the culprit anyway and just adding 10pf
across the minimum pf of the cap is not the answer. Witout knowing
problem frequencies, Tune C, added C + leads, and all other factors into
the equation it sounds like a typical ham fix...it may work for some but
be a disaster for others.
Adding a series cap in that amp works better IMO since the stray L/C
causing the arcing problem appears to be due to the shorted turns of the
coil. By carefully looking for VHF energy on all bands, I have found
that adding 10pf ( just a 1KV Silver Mica or NPO 3KV ceramic with
shortest leads possible) across the 20 and 40M taps right at the switch
totally eliminated problems in several ALREADY arcing amps. In never
arced 220-221amps with the wide spaced Tune cap I have run external
supplies of 3600V and 1800W + output without arcing with the series cap
in place. I have only tried 10 and 12pf in the 220 but the results are
repeatable which I believe is a requirement.
As has been previously pointed out, there is no guarantee that the series
cap will work on every antenna combination. With a Bird dummy load there
is no problem. With the average feedline to say a tribander being 100' or
so the flat loss in the coax will flatten out the VSWR antenna response
at VHF/UHF. I have no idea what an antenna tuner will do...I dont use the
darn things! Maybe add a parallel 10pf with very short leads across the
220 output SO-239 may help...any ideas?
In any case I am very pleased to see Arlen, Ian, John and Steve taking an
active interest in this. Perhaps others with credentials will join them.
73 Carl KM1H
.
.
There seems to be a lot of emotion in
>this debate, and I've not seen anything in it that suggests that the
>experiement would take nearly as much effort as people have put into
>writing vitriol. If this is to work, cogent arguments must be put
>forth, and more than one.
>
>Arlen
>
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