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Re: [Amps] Parasitic Oscillation

To: Will Matney <craxd1@ezwv.com>
Subject: Re: [Amps] Parasitic Oscillation
From: R.Measures <r@somis.org>
Date: Wed, 3 Nov 2004 21:23:15 -0800
List-post: <mailto:amps@contesting.com>

On Nov 3, 2004, at 5:40 PM, Will Matney wrote:


Hal,

Marv made a very good point earlier when he mentioned about Bill Orr being associated with Eimac and said "there is no such thing as an amplifier that does not have parasitics! He made it clear that at some frequency, under some mix of power, drive, settings etc., any amp can be made to oscillate."

I think I would more tend to believe someone with Eimac who actually makes and tests the tubes than anyone else. From personal experience I have seen it happen due to long lead lengths in some crudely designed amps. Actually the crude part came from the builder being too tight to build it the correct way.

A person would think the SB-220 bad but do you remember that 10 or 12 tube 3-500Z box on eBay for sale with all the problems seen? I would think it would have been a nightmare.

Tom Rauch's webpage with the SB-220 amp shows testing one with the parasitic suppressors *still connected*. Keep in mind that this is the only amp that was tested and he states he doesn't have time to test more. Now I would think one would want to do the test with NO suppressors installed to see what happens.

Will -- I did no a suppressors experiment with my SB-220 on 40m. The amplifier was not stable.
- In my experiences, "not enough time" usually has nothing to do with the availability thereof..


By testing with them installed, only shows that one amp was working correctly with its parasitic suppressors in circuit! Plus, not every SB-220 is the same,

The major difference in SB-220s is the particular tubes that happen to be plugged in.


not every wire the same length or in the same place. Really, all commercial amps aren't either. Plus those tubes in that amp didn't look no where new to me so the gain may have been lower than fresh tubes

However, this is not always the case. The hottest, squirreliest pair of 3-500Zs I ever tested had a couple of hundred hours on them.


...
Richard L. Measures, AG6K, 805.386.3734. www.somis.org

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