[AMPS] input Q upgrade

[Charlie Ocker]

nospam4me@juno.com wrote:
> 
> Hi Charlie,
> 
> Glad to see you going with the g-grid circuit. You'll find the 4-400
> amplifier
> slightly harder to drive vs the similar 3-400/3-500Z.

It took me awhile to "see the light", but I think that I'm now on
track!  Tnx!

> I have most of the input circuits for the common tubes, the trouble is
> the
> paperwork was done before solid state final exciters. The lower Q of the
> older designs plays havoc with some exciters. I've seen a real
> interesting
> oscillator made from an early SS exciter final where one wasn't wanted.
> 
> I'm in process of rebuilding my personal SB-220 with all the current
> fix's,
> during last nights late night tune up into a termination, I measured the
> factory SB-220 swr using my TS-940.  The best obtained was about 1.6 to
> 1 sweeping the entire 80/40/20 meter bands. Although my 940 seems to
> drive it fine, "your results may vary."

I don't have any problems driving my SB-220 with my TS-930.  I'm hoping
that will stay the same with the gg 4-400's.

> I hoped to avoid rebuilding the input for a higher Q, but it looks like
> it
> should be a "must include" for a new project.
> 
> Rich mentions the SB-220 input factory Q about 1.6 and suggests more.
> I agree with that opinion.  His web site probably has the information
> you need.  I can scan the 4-400 inputs I have (better than nothing) here
> for the sonic server, but it'll have to wait until next week.  I'm in the
> middle of another server upgrade process.

I've been to Rich's excellent web site many times, and have read through
everything a couple of times, more on some parts than others.

I would appreciate any info that you have.  So far, as best as I can
tell, the input Z for a pair of 4-400's gg is about 70 ohms R, but I
don't know what the C from cathode to ground is.

I found some shareware on the ARRL web page, actually, it was the Oak
repository, that was written about 10 years ago by W5FD.  It calculates
Pi-L and Pi network values for the tank, and also will calculate the
input Pi net values.  I've played around with it, and it outputs
"reasonable" values that are in the ballpark with what I've seen in
published designs.

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