[AMPS] YC-156 Input impedance

[Phil Clements]

----- Original Message -----
From: "PAUL HEWITT" <wd7s@att.net>
To: "Phil Clements" <philk5pc@tyler.net>
Sent: Wednesday, October 03, 2001 9:04 AM
Subject: RE: [AMPS] YC-156 Input impedance


> It's too bad your engineering skills
> don't match your ability at being a
> smart-ass.  Been there-did it wrong is
> probably more accurate.
>
> PAUL HEWITT
> WD7S PRODUCTIONS
> QRO HOMEBREW COMPONENTS

The response to your post to me and the reflector was
tailored you your terse and pithy remarks. It is very sad
that you have no sense of humor, and hate to be proven
wrong.

I gave the guy good advice, and backed up by Tom Rauch's
calculations, and my actual operating conditions with a working
YC-156 here on the desk. The guy has not asked for more details,
so I assume my advice was helpful to him.

Most folks who know me will tell you that my engineering skills
DO match my ability at being a smart-ass. I have been there
(first home-brew amp in 1954) and been "doing it" ever since.
I try to give people honest advice here on the reflector, tailored
to the question asked. I try to refrain from telling how to build
a watch when asked what time it is.

(((73)))
Phil, K5PC

> Subject: Re: [AMPS] YC-156 Input  impedance
> Sent: Tuesday, October 02, 2001 2:22 PM
> > 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




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