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Re: [Amps] Ceramic tube temp too low?

Subject: Re: [Amps] Ceramic tube temp too low?
From: Gerald Williamson via Amps <>
Date: Mon, 14 Mar 2016 11:13:37 -0400
List-post: <">>
Hi Steve,
Many water cooled GS35B amplifiers are in use, mostly on 70cm. Do a  Google 
search for "water cooled GS35B" and a lot of information will come  up.
The temperature concern is a non issue as the only requirement is for the  
cathode to reach a proper temperature to emit electrons. All of this happens 
 inside a vacuum much like a thermos bottle for hot/cold liquids. 
An added benefit of water cooling at the higher frequencies is a big  
reduction in frequency drift of the plate resonators, especially the strip line 
type. When the are heated due to close contact with an air cooled anode, 
they  change dimensions at the rate of around 20 parts per million per degree 
C. While  that may not sound like much, a high Q resonator can move off 
frequency enough  in a few seconds to drop the power out put 3 dB or more. It 
not enjoyable to  operate cw sending with one hand while watching power and 
adjusting the plate  tune with the other hand. Yes, I have been there and 
done that.
True coaxial resonators are much more frequency stable (and efficient) but  
that is another story/topic.
Gerald K5GW
In a message dated 3/14/2016 9:44:30 A.M. Central Daylight Time, writes:

I am  thinking of liquid cooling VHF/UHF GS-35b tubes to dodge noisy fans 
and  and tuning drift.

But what will be the situation with operating these  tubes at lower 
temperatures?  I cannot see that they have a rated  operating range, just 
a maximum seal  temperature.


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