[Amps] Parasitic Oscillation

[R.Measures]

From: R. Measures <r at somis.org>
Date: August 17, 2005 4:15:53 PM PDT
To: "David Lisney" <g0fvt at 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