From: R. Measures <r@somis.org>
Date: August 17, 2005 4:15:53 PM PDT
To: "David Lisney" <g0fvt@hotmail.com>
Subject: Re: [Amps] Parasitic Oscillation
On Aug 17, 2005, at 12:06 PM, David Lisney wrote:
> Hi, I stumbled across an enlightening article discussing the
> construction of
> a twin 4-400 amplifier, it seems the prototype had a parasitic problem
> at
> 160Mhz, it seems the fix was found referring to an Eimac engineering
> bulletin of the time. The article appeared in QST, April 1957...
> completed
> amplifier used a series tuned circuit with damping resistor from the
> tube
> grids to ground, incidentally it used NO parasitic stopper in the
> anode.
A series tuned circuit with a damping R Is a parasitic suppressor
because it reduces the amount of anode-resonance (here, 160MHz) damped
wave ringing signal fed back to the grids by the total grid-to-anode C
of c. 0.30pF (XC = 3100-ohms).
Also, there is no such animal as a parasitic stopper. The best one can
do is to try to keep them at bay -- and use glitch protection.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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