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Re: [Amps] a common topic here tspa

To: amps@contesting.com
Subject: Re: [Amps] a common topic here tspa
From: Ian White G3SEK <G3SEK@ifwtech.co.uk>
Reply-to: Ian White G3SEK <g3sek@ifwtech.co.uk>
Date: Thu, 7 Apr 2005 11:26:59 +0100
List-post: <mailto:amps@contesting.com>
R. Measures wrote:
>> No, I'm simply saying that the Eimac tube guys that I knew and worked
>> with said a lot of what passes for "truth" is a bunch of nonsense.
>> In their experience, every case of "parasitic problems" in 8877 amps
>> could be resolved by properly grounding the grid
>
>Did the 8877 design team use improper grid-grounding that resulted in 
>the "oscillation condition" they observed that caused gold to evaporate 
>from the grid of the DUT?
>
That seems to be conflating two different stories, on the basis of 
information from an individual Eimac employee which the company 
subsequently said was incorrect.

The "oscillation condition" in question was not a VHF parasitic as we 
know it, but can only arise in extremely large tubes that are big enough 
to have their own internal VHF resonances.

What causes gold evaporation is overheating - that much seems obvious. 
What caused the overheating in any particular case is entirely open to 
question.


-- 
73 from Ian G3SEK
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