[HomeBrew] 4-65A amplifier info?

[Brian Burns]

Hello Carl,

~ I guess some on here don't like posting to the group Brian.

When I reply to an answer on the mailman.qth.net lists. the reply page that
comes up in my Microsoft Outlook has the individual's email as the default,
rather than the list's email. I have taken to changing it so that everybody
sees my reply, but others don't seem to notice. 

~ As far as linear use consider that at only 130W plate dissipation for a
pair the amp will be about as robust as a pair of 811A's. IOW, pretty
useless as an AM linear since the Viking already will output 100W.

~ A SB-200 with about 320W Pd is good for about a 120-150W carrier.

~ Also realize that with the lower efficiency AND the steady carrier the
plate transformer needs more current capacity than CW and SSB. There is
where controlled carrier screen modulation can be beneficial.

~ For a somewhat (barely) meaningful increase over the Viking you would need
a 400W carrier for a 6dB increase and that puts you right at the legal limit
of 1500W PEP. For nitpickers the 375W is for a sine wave, not asymetrical
speech.

Well, here is my thinking, mostly subject to economics, and the generosity
of my friends--and always subject to revision when wiser hams like yourself
point out the errors of my ways! Hey, flattery gets you everywhere, doesn't
it? See Dale Carnegie's famous book (;->)...

The Heath amp in good working order costs money. I don't have to ask how
much, because I don't have it, whatever it is.

I'm starting with the Viking 1 as an all band exciter because it
(supposedly) can be made to cover the WARC bands, as well as all the others.
It contains all the audio circuitry, and puts out, with the 4D32 final, and
a marginal modulation transformer, perhaps a reliable 80 watts. Part of that
80 watts goes to drive the linear, and part goes on through to the antenna
(?).

Wayne Mills N7NG, my old high school buddy, answered my email last night,
and will be bringing me the plate transformer from that diathermy machine
that we stripped over 50 years ago--also a pair of 866 mercury vapor
rectifiers! Since his wife is from my town of Fort Bragg, CA, they will
bring it in their car the next time they come over to visit relatives--no
freight charges! The next size larger transformer "comes on wheels"! I have
no idea yet what the capacity of that thing is, but it is a second cousin to
a pole-pig! I just hope that Wayne doesn't strain his back lifting it!

I'll have two free 4-65's and a couple of HV tuning caps in stock, and since
I'm interested in around 350 watts out on 160, 75, and 40, how about adding
a couple more 4-65's in parallel--they seem to be reasonably priced? I
should think that inter-electrode capacity would not be a problem on these
lower bands.  

My antenna tuner, A Harvey Wells Z match is rated at 500 watts input to the
final, and in class C at 70% efficiency that would mean that it could handle
the 350 watts out of the linear. 

Grounded grid(s) amps have the reputation of being readily built by
home-brewers, and are relatively simple (no neutralization?)

So this all seems to add up to the cheapest way to get a worthwhile boost in
AM signal on the lower bands. I'm sure there are some "flaws in the
ointment" here, so what do you think?

Cheers, 

Brian

 





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