Re: [Amps] Need info on adding WARC bands to an old HB 4-1000A amp

[Scott Townley <nx7u@arrl.net>]

John (and whomever else is interested).
1. As noted previously, dip meters are just wonderful things.
2. I am retooling a 3-500z amp.  The HV stack is a B&W800, and down the 
road->2x1000pf 5kv centralab doorknobs->Ohmite Z-50->2x1000pf 5kv 
centralab->B+ in.  I just got done dipping the entire stack (short the top 
of the B&W800 to ground, so I'm testing the entire HV bias system) and had 
a very pronounced dip at 22.5 MHz.  I got lucky!
3. I also did the "reverse engineered" pi-section...meaning, I terminated 
the B&W800 in 3300ohms (my desired plate impedance) and hooked up my Autek 
VA-5 to the amp output.  Then I select the band and tune/load until I get 
the lowest VSWR...this is in effect tuning your output network in 
reverse.  If the plate choke is series-resonant you won't be able to get a 
match (or maybe it will come only with really odd values of Ctune and 
Cload).  So that may be another alternative.

PS this is all in place in the final amp chassis.

As always, if I'm full of <stuff> someone shout out...this isn't a shy list 
anyways :-)

At 08:13 2004-12-03, John Becker wrote:
> I'm new to this list, and I apologize if this has been asked before, but I 
> didn't find what I needed in searching the list archives.
>
> I have a HB 4-1000A amp, covering 80-10, which I built in 1969 from a 
> design in the Radio Handbook. I only have a Xerox of the article, so I'm 
> not sure which edition of the handbook it was in. The title of the article 
> is "The Utility 2 Kilowatt PEP (U-2) Linear Amplifier".
>
> I want to put this amp on the WARC bands, but I've heard that the B&W 800 
> plate choke is self-resonant somewhere close to 12M, and is likely to go 
> up in smoke if I try to tune-up on that band. Is this true? If so, what 
> solutions have been found to be effective? Thanks!
>
> 73,
>
> John, K9MM
>
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