[Amps] Building an Amp 101

[Carl]

----- Original Message ----- 
From: "Jim Thomson" <jim.thom at telus.net>
To: <amps at 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 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.
>
> 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