On Jun 9, 2006, at 7:37 AM, Gudguyham@aol.com wrote:
> I have noticed that some amplifier manufactuers discuss "exciter
> overshoot"
> in their operating manuals. Apparently some exciters at the moment of
> initial RF keydown will for a split fraction of a second put out
> full power
> regardless of the RF setting on the exciter, and even a split
> second burst of power
> beyond 100 watts.
I've measured as much as 170w initial surge from an adjusted to 100w
radio.
> It is a known fact that a bandswitch or a tuning capacitor
> arc can occur if too much drive is applied with too light loading
> to the
> amplifier.
However, tubes are emission limited, so there's a practical iimit.
For example 3-500s are linear up to c. 1.2a-pk and they can be driven
to c. 1.6a-pk, but that's about the end of the road since at that
point they are pretty much saturated.
> I know that Alpha amps respond very quickly to sudden spikes in
> overdrive. One ham I know had a major problem with his Alpha amp
> using an Icom
> exciter. Could some bandswitch and tuning capacitor arcs be
> attributed to
> exciter overshoot?
Surely, but since the amount of overshoot is emission-limited by the
electron tube's cathode, the Tune-C would have to be pretty marginal
to start with in order to arc.
> I know from personal experince that some of the arcs I have
> seen occured when the initial drive from the exciter was applied. THE
> QUESTION IS..............
>
> Has anyone measured exciter overshoot? It would have to be done
> with a
> scope I am sure since a meter would never react that fast to see it.
correct
>
> Lou W1QJ
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>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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