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[Amps] Thunderbolt Linear amp

To: <amps@contesting.com>
Subject: [Amps] Thunderbolt Linear amp
From: 2@vc.net (2)
Date: Fri, 10 Jan 2003 08:33:03 -0800
>       Has any of you tried some easy improvements to the old Johnson 
> Thunderbolt?
>I just got a parts unit that I plan on restoring but I may not make it 
>original. One thing that
>strikes me is the low plate voltage and the small diameter wire on the 
>roller inductor.

The anode supply needs to be converted to resonant choke filtering.  
Swinging-choke filters cause wild Swings in output V in CW and SSB modes 
-- but for AM linear and RTTY, the anode V will be stable.
--  Smallish diameter wire  (#12?) in the roller coil can be better 
tolerated if cooling air is directed at the coil and a 1/4" d. Cu tubing 
10m coil is added..

>  I suspect the output component ratings voltage and current may be a 
>limiting factor.

My guess is that the tune-C will not arc.

>       A full wave bridge rectifier would be an easy way to increase plate 
> voltage,
>if bypass and plate tuning capacitors allow. However many of these old 
>transformers do not like
>having their center tap  floating at high potentials.

Good point.  So bake the wife some toll-house cookies and then dry the 
transformer out in the oven for a while.  When dry, pot the transformer 
yourself with polyester fiberglass-laminating resin.  see:
http://WWW.VCNET.COM/measures/D.amplifiers.3.html

--  However, if you increase the anode supply V, tube gain will also 
increase but feedback-C will remain the same.  Thus, a lower VHF-Q 
parasitic suppressor might not be a bad idea -- although it will result 
in c. 2% less power at 29MHz.  

cheers, Bill

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
end


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