>
>Jon says:
>
>>Is the amplitude of a spark that is generated by hotswitching a 100W
>>signal on the input relay really large enough to drive the tube and
>>thereby generate a change in anode current on the output?
>
>Isn't this one of the 'does the sound exist in the forest if no one is there
>to hear it?' type arguments? If there's an arc at the input applied to the
>amplifier, it is coincidental in arriving at the input with the input RF
>which will drive the amplifier and change its plate current anyway.
>
>Personally, I disagree in general with Rich about parasitics and killing
>tubes, although I concede that a parasitic could boil gold on a tube with
>low grid dissipation. It's just funny that commercial manufacturers of
>amplifiers (commercial meaning for commercial market, as opposed to the
>amateur market) just don't seem to get a problem.
? One of the seemingly better articles on the treatment of vhf
parasitics was written by a commercial amplifier engineer who worked for
the General Electric Co. ("Parasites and Instability in Radio
Transmitters", by G. W. Fyler, *Proceedings of the Institute of Radio
Engineers*, September, 1935) Fyler concludes that "parasitic circuits
should be damped with resistance".
- RE: commercial amplifier problems: One manufacturer who made MRI
amplifiers for General Electric's medical division reportedly had an 8877
failure problem. The manufacturer was told by G. E. to fix the problem.
The amplifier manufacturer tried to blame Eimac. whereupon G. E. cancels
contract. As I recall, the amplifier manufacturer who tried to blame
Eimac stated that he had seen many gold-sputtered tubes.
>I also question whether
>overheating of parasitic suppressors isn't down to them getting very hot
>because of physically where they are,
? In all but conduction-cooled and water-cooled situations, vhf
suppressors typically live in fast-moving air.
> and to them being under rated for the
>amount of dissipation of the fundamental they get, especially on 10, 12 and15
metres.
>
? 'Tis a sticky wicket. Larger resistors have more intrinsic-L. In a
parasitic suppressor, more intrinsic-L in R decreases the desired
stagger-tuning effect. // The 10m dissipative burden in a suppressor-R
is greater than one might think. {see March, 1989 *QST*)
>
- later, Peter
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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