[Amps] Clipperton-L parasitic suppressors

[Bill, W6WRT]

ORIGINAL MESSAGE:

On Sun, 14 Mar 2010 00:16:41 +0100, Dave White
<mausoptik at btinternet.com> wrote:

>
>Isn't the real cause that the tube and/or circuit has Q at VHF? So isn't the 'cure' that we try to lower the Q at VHF whilst trying to keep Q at the fundametal that we're interested in?  It may be a moot point as to whether we're treating cause or effect.  Search me, mate.  That's too deep a question at this time on a Saturday night after a few glasses.

REPLY:

For a tube to oscillate, the circuit Q has to be high enough on both
the anode and grid circuits, enough so the gain is one or more and the
phase of the fed-back power is correct or nearly so. 

In other words, the problem can be attacked in either the anode or
grid circuit, or both. I have built several amplifiers with no
parasitic suppressor at all, but where the grid circuit was designed
to have a very low impedance at VHF, and the amps were all perfectly
stable. 

Basic oscillator theory. 

73, Bill W6WRT