----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Sunday, January 19, 2014 9:34 PM
Subject: [Amps] Building an Amp 101
Date: Sun, 19 Jan 2014 13:56:44 -0500
From: "Carl" <km1h@jeremy.mv.com>
To: "Fuqua, Bill L" <wlfuqu00@uky.edu>
Cc: amps@contesting.com
Subject: Re: [Amps] Building an Amp 101
The Henry 8K Ultra uses solenoid contactors to select fixed caps in lieu
of
a bandswitch. The inductor is a rotary and a small vacuum cap is used for
fine tuning, both motor driven with 10 turn pots or presets.
Carl
KM1H
## The 8 k ultra uses NO conventional tuning cap. On 15-10m it uses the
33 pf of tube
C for the tune C. On 20m, a 25 pf NPO 15 kv HT-57 is switched in.
And more C
on the lower bands. The actual tune control IS the roller inductor. A
500 pf vac cap is used as the
load cap..and is heavily padded on the lower bands. Henry used modified
solenoids to simultaneously
chassis ground the cold ends of both the tune and load padding caps.
They also used TWO rollers,
ganged together, that turn at different rates. Between the myriad of
endless modified solenoids and also the
boxful of HT-57 NPO caps used.... henry went to a lot of trouble to
eliminate the conventional vac tune cap.
IMO, the 8 k is an example of how NOT to do it. The RF deck is a
pita..with so many failure prone points
in it. The last real amp henry built was the 4 k ultra, with a vac tune
cap...and a vac load cap.
## For a HB amp..keep it simple. A single triode tube in GG is all you
need. Don’t mess with multiple tube
grid driven designs..and their associated regulated screen supplies. A
chinese 8877 will do the job....and loads
of 8877 proven designs over the years. If you want more power, use a
3CX-3000A7. I would not mess with
a PI-L design either. It buys you nothing but a pita. A simple PI is
more than adequate. Stay away from using
torroids in the tank circuit too..more pita. Cu tubing is dirt cheap at
home depot. Build it like a tank..and it will last forever.
Jim VE7RF
I guess I wasnt clear enough as I did not mean to imply the vacuum variable
was a TUNE cap. I capitalize between Tune and tune and Load and load to
signify what Im referring to.
I just sent another repaired 8K on its way and I havent had an output
section RF deck failure yet.
Carl
KM1H
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