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[AMPS] adding a second tube

To: <amps@contesting.com>
Subject: [AMPS] adding a second tube
From: measures@vc.net (Rich Measures)
Date: Sun, 10 Aug 97 11:41:21 -0800
>Esteemed Reflectees:
>
>        The comments expressed recently regarding adding a second tube to
>the existing one in the Alpha 77 series, without altering the tank, has made
>me think about the practice as it applies to other amps. I noted lots of
>folks are adding a 3rd 8874 to their older Alphas, and the current AL-800
>will apparently ...

...allegedly seems to be a bit more like it.

>...take a second 3CX800A with no other PS or tank changes to
>make it an AL-800H. Possibly someone else makes a 1-holer ready to take a
>second tube. 

To yield a tank operating Q of 12 with two tubes (operated at double the 
anode current of a single tube), a 1-holer that is "ready to take a 
second tube" would need an original tank operating Q of 24.  
>
-  For example:  When the second tube is added to a 77dx, and the tubes 
are driven to 2A of anode current, the stock tank's operating Q on 160m 
drops to about 5.9.  IMO, this is not good engineering practice.  To 
increase the operating Q to 12, C-tune and C-load need to be roughly 
doubled and L needs to be roughly halved.  Since P=I^2 *R, it might be 
worthwhile to increase the surface area of the tank inductors when the 
second tube is added--because the RF circulating current doubles. 
-  Are we to believe that recognized amplifier "experts" are exempt from 
Ohm's Law?   
Rich---

R. L. Measures, 805-386-3734, AG6K   


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