Date: Mon, 22 May 2017 15:53:24 -0600
From: MU 4CX250B <4cx250b@miamioh.edu>
To: TexasRF@aol.com
Cc: "jmiklos@windstream.net" <jmiklos@windstream.net>,
"amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] Henry 3 KD Premier with 8877
<I'm not familiar with that particular amplifier, but low 10m
<efficiency is a common problem with 8877 amplifiers. In one of my
<homebrew amplifiers, I had low efficiency in the 40% range until,
<following a suggestion from Bob Sutherland W6PO, I relocated the tuned
<pi input circuit capacitor C2 from the input band switch directly to
<the cathode pin on the tube. Incredibly, efficiency jumped up into the
<60% range. I was dumbfounded.
<73,
<Jim w8zr
## here is the manual.
http://www.radiomanual.info/schemi/ACC_PA/Henry_Radio_3KD-Premier_8877_serv_user.pdf
Its a bit of a screw ball design. Its uses a PI-L..but with no conventional
C1 variable tune cap. Instead it uses
a bandswitched mess of fixed. 25 pf npo hec caps. The 28 uh roller coil IS
the... tune control. They also have a switch
to short out most of the roller coil. It has NO grid current overload trip out
circuit. It also uses just a single 25 uh plate choke
to cover 1.8 to 30 mhz continuously.....with a pair of 4700 pf @ 15 kv bypass
caps at the base of the plate choke.
## he could take C31..the 210 pf output cap on the 10M tuned input...and
re-locate it to the socket it self, wired between chassis
and cathode of 8877. Another method is to use parallel or even triple
RG-58... with all center conductors bonded..at each end..and ditto with
the braids at each end.... to make 25 or 16.66 ohm coax. Then use the low
25 or 16.66 ohm coax from output of tuned input assy to the
cathode. That will have the same effect as placing some C right at the
cathode. Re-locating the C31 cap would be simpler. But check and see
if the input swr is still ok.
Jim VE7RF
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