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
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