-----Original Message-----
From: Jon Ogden [SMTP:jono@webspun.com]
Sent: Monday, April 20, 1998 12:16 PM
To: km1h @ juno.com; amps@contesting.com
Subject: Re: [AMPS] parasitics
>If it passes those tests AND as long as the suppressors are OK, I can in
>NO WAY accept that a parasitic will occur during use. Arcs on standby are
>gas or barnacles in the tubes....note that those arcs rarely if ever are
>associated with capacitor or switch failure but can blow grid chokes and
>tubes.
I've read Rich's information on his webpage and I think I can repeat his
theory:
He says that whenever you have a change in anode current in a tube that a
small, damped VHF signal will result. He says you can observe this with
an O-scope or a spectrum analyzer. If there is enough Q in the VHF tank
circuit in the PA, then an osicallatory condition could occur.
While I agree that the whole tank circuit in a tube IS VHF resonant, I am
not sure of how a transient current condition in the tube can produce a
VHF ringing. I would like to know if anyone has seen this on a piece of
test equipment. If true, it does add a lot of credence to Rich's
theories.
ALL tubes contain parasitics.
[Dick Ehrhorn:] Jon, I think it'd be much more accurate to say that
(virtually?) all circuits contain parasitic reactances and therefore
parasitic resonances, which lead to the potential for parasitic
oscillations when used with many or most types of tubes.
There is a BIG difference between a
parasitic and a parasitic oscillation. It's easy to get them confused.
A parasite in a tube is the lead inductance and stray capacitances, etc.
that exist in the real world. Even a leaded capacitor has parasitics
(lead inductance).
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@webspun.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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