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Re: [Amps] parasitic oscillation techniques

To: <amps@contesting.com>
Subject: Re: [Amps] parasitic oscillation techniques
From: "k7fm" <k7fm@teleport.com>
Reply-to: k7fm <k7fm@teleport.com>
Date: Mon, 24 Aug 2009 20:48:15 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Rich Measures name has come up, as well as purported comments from Eimac 
about his advice.  The date of Rich's first article on parasitics was April 
1986, in Ham Radio.  Notably, it said nothing about nichrome.

The title was "Grounded-Grid Amplifier Parasitics (Simple cure extends 
amplifier life).

In the article, Measures mentions that his first writing on the subject was 
in "ham notes" in October of 1982.  In those notes, he claimed that he 
copied the Collins grid suppressor circuit and the amplifier did not 
oscillate.  In the 1986 article, he claimed he was smarter and found that 
using 3 paralleled R-C supressors on the grid of each tube, using 3 x 47-75 
pf caps and 3 x 75-100 ohm resistors on the grid of each 3-500 tube 
eliminated parasitics.  He also recommended a series connected R-C 
combination in the cathode, comprised of  a .01 cap and 3 x 10 ohm 
resistors.

He wrote that when he applied these remedies to a 4-1000 amp that was 
unstable at 4,000 volts, the amplifier showed no sign of instability even 
when run on 9,000 volts.

At the conclusion, he gave a detailed explanation of why these remedies 
solved the parasitic problem.

I can only assume that he discarded these remedies when he came up with his 
later remedies, and usually remedies are discarded when they do not work as 
well as promoted.  It is possible that Eimac made their "alleged" statement 
about Rich Measures after these first remedies were applied, and maybe they 
were not talking about his later remedies.

73,  Colin  K7FM


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