[Amps] Building an Amp 101
jim.thom at telus.net
Sun Jan 19 21:34:39 EST 2014
Date: Sun, 19 Jan 2014 13:56:44 -0500
From: "Carl" <km1h at jeremy.mv.com>
To: "Fuqua, Bill L" <wlfuqu00 at uky.edu>
Cc: amps at 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.
## 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.
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