[AMPS] YC-156 Input impedance

[Phil Clements]

Phil Clements
410 VZ CR 4903
Ben Wheeler, TX 75754

----- Original Message -----
From: "PAUL HEWITT" <wd7s@att.net>
To: "Phil Clements" <philk5pc@tyler.net>; "KD4LYH" <kd4lyh@earthlink.net>;
<amps@contesting.com>
Sent: Tuesday, October 02, 2001 2:22 PM
Subject: RE: [AMPS] YC-156 Input impedance


> I am very curious how you arrived at
> that input impedance.  As you know EVERY
> set of operating parameters results in a
> different drive impedance and the
> original question did not supply any
> operating information.  Are you
> guessing?  Or worse yet are you reading
> from a data sheet under typical
> operation?  I'm sure that nowhere on the
> 3cx15000b7 data sheet is there any
> information, (except the constant
> current curves), for operating this tube
> at the reduced power level(I hope) the
> builder plans to use.
> Paul

Wrong, Kimo-Sabe!
The Eimac data sheet plainly states that typical performance
(measured data) to 30 mhz that the cathode input impedance
is 24 ohms. It also states that a resonant  input circuit should be
installed at the cathode, and it is to have a Q of 5 or MORE.
This assumes an anode RL of 1000 ohms.

For folks that would go to all the trouble and expense to put
one of these tubes and then operate it at reduced output, a
few bucks more will buy you a tuned input circuit with a roller
coil and two variable caps.

People might wonder why anyone would use a YC-156.
Pulls are beginning to show up at reasonable prices from
the usual MRI repair sources. They require no socket, they
bolt right to the chassis. The 6 kv supply that is powering a
4-1000A amp is just perfect for the YC-156. And last but not
least, it should last a lifetime loafing at 1500 watts.

On my YC-156,I use my usual choice of input circuit. I buy
them from Henry radio, all pre-wired and pre mounted; 160-10
meters. They are 50 ohms in and 50 ohms out. I then go through
a 2:1 transformer (an old Alpha 77SX trick) to arrive at 25 ohms
with a Q of 5+.

I told the man 25 ohms because that will get him in the ball park
starting out. We have a lot of headroom here...what's a few DB
with a 15 DB gain bottle?

Been there, done that, got the "T" shirt.

(((73)))
Phil, K5PC





--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com