> 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.
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