On Nov 3, 2004, at 11:02 PM, Jan Erik Holm wrote:
Will,
This is interesting. I have had flashovers in the tank circuit
in my 4-1000A amp being more then 1 inch long.
Wow, Jim, that's got to be >26,000V.
What you write below could explain it.
73 Jim SM2EKM
-----------------
Will Matney wrote:
Rich,
>The major difference in SB-220s is the particular tubes that happen
to be plugged in.
I would think so too!
> >not every wire the same length or in the same place. Really, all
commercial amps aren't >>either. Plus those tubes in that amp didn't
look no where new to me so the gain may have >>been lower than fresh
tubes
>However, this is not always the case. The hottest, squirreliest
pair of 3-500Zs I ever tested >had a couple of hundred hours on them.
Hmm, one would assume that the more hours on a set of tubes, the gain
would drop due to the emissions being lower than a new tube. I can't
recall if the test listed the output power on the SB-220 or not
without re-reading it. What his conclusions were based solely on was
the fact that the VHF frequencies were several dB's less than the
operating frequency with the suppressors in the anode leads. To me,
like you had done, I would want to see the test less any suppressors.
As Marv said about Bill Orrs comments, any certain time with the
correct conditions, a VHF oscillation might happen.
Now, I have some experience with plasma arc cutting machines, the
large ones mind you. The way the arc is started is the use of a very
high frequency. They use something similar to a spark gap to generate
a very high frequency arc. This arc then causes the main conductor at
the tip to arc to the material. This happens after the oxygen is
flushed away from the tip and material by a forced jet of CO2, or CO2
with helium (shielding & cutting gas). Once this larger arc (cutting
arc) is established, the high freq generator drops out. Tig welders
work by a similar process. One must keep in mind that at VHF
frequencies, arcing is way greater than at High Frequencies. Ignitron
tubes used in Flash Welders use a high freq put on the control stud
which arcs down to a mercury pool. This then allows the arc to start
between the anode and cathode (cathode being the mercury pool). It
would look to me that a small VHF generated arc from a possible
oscillation would cause a larger arc from the power stored in the
tank circuit. This could very well burn the contacts out on a
bandswitch. That's just a theory, not fact. Any thoughts on this
would be welcome from all.
> ...Richard L. Measures, AG6K, 805.386.3734. www.somis.org
Best & 73's
Will Matney
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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