>
>I do not wish to impede the quest for knowledge, nor the exercise of clear
>thinking - or even unclear thinking, but it seems we have had a never-ending
>debate about parasitic suppression.
>
? rubbish. Nothing was heard until October, 1988 *QST* Magazine.
>So, I wish to include my 2 cents worth. I have a number of home built and
>commercial amps. i have no parasitic problems with any of them. I have
>never destroyed a tube with parasitics - nor by any other means. The only
>SB-220 I had to repair was for a friend who turned the bandswitch while
>tuning because he was not looking and thought it was the plate tune control.
>
Which contact burned? Were you present when the contact burned? ///
The above story seems unlikely because tank potential is maximal only
when the tank is nearly resonant. As soon as the band switch is in the
wrong position, the tank is grossly out of resonance. Furthermore, the
drive delivered to the tube plummets. When I turn the bandswitch in my
220, virtually nothing happens. The output drops. Additionally, the
bandswitch in a 220 is continuously shorting, so how could arcing take
place during switching?
>When I build a cathode driven amp, and before using, I drive it at the
>cathode - with a constant output signal generator and no tuned circuit - and
>monitor the plate rf voltage with a 500 mhz voltage probe for various
>conditions of the output tank circuit - loaded and unloaded. If there are
>no hot spots (other than the frequency where the tank circuit is tuned), a
>parasitic oscillation cannot be sustained. If there is a hot spot, it can
>be addressed by correcting the problem or by constructing a parasitic
>suppressor. If you know what the problem is, you do not need a do
>everything parasitic suppressor.
? How do you construct a VHF suppressor for one frequency?
>.....
cheers, Colin
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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