[Amps] HV PS chokes to give away

[Larry Carman]

Hi Everyone,

I have a couple of HV power supply chokes that were removed from
the Henry 2500 watt RF gens running the 3cx3000a7 tube.
I believe the power supply delivered  about 4000 volts at 1 amp.
They are free to anyone who wants to pick them up. I'm located in
The Colony, Tx. The chokes are 6 1/2 by 5 1/2 by 8 inches and
probably weigh about 30 lbs. They are in good condition.
You can contact me at 972-625-2123. Leave message if no answer.

Regards all,
Larry N5BIP

----- Original Message ----- 
From: "R.Measures" <r at somis.org>
To: "Stan C." <kf6ikc at sbcglobal.net>
Cc: <amps at contesting.com>
Sent: Tuesday, August 10, 2004 12:11 AM
Subject: Re: [Amps] 4CX5000A question



On Aug 9, 2004, at 2:04 PM, Stan C. wrote:

> Hello.
>  I am thinking of building a amp using the 4CX5000A tube. I have a few
> question that I can not seem to come up with the answer to. So I am
> hoping that some of the knowable folks here on the list can help me.
> Keep mind I am not a engineer,so please give me your answers in layman
> terms.
>
> 1) How do you determine the value and rating of the screen bleeder
> resistor.

Stan --  This subject could be of benefit to other builders of tetrode,
AB1 amplifiers, so I posted it to the entire group.
-  30mA of screen-shunt bleeder-I seems to be enough to protect an 8170
or 8171 from (runaway) reverse screen-I condition during tune-up. ///
note -- reverse screen is entertaining for those who enjoy fireworks.
>
> 2) How do you regulate the screen supply.

One way is:
http://www.somis.org/D-a-08.GIF
However, the raw DC must be >10V higher than the desired screen-V.

> I was going to just use a transformer that rectifier to the right
> voltage and call it good. Please let me know if this will work.

This approach will work, but the filter-Cshould be the resonant-choke
type and the filter-C should be larger than normal to reduce screen-V
fluctuation during voice modulation.

> Is the concern in the voltage going to high or sagging???

Both.  Screen-V needs to stay put for best linearity during voice
modulation, however, with a sloppy (high ESR) screen supply, and using
a 2-tone test with 1kHz or so tone spacing, the IMD test will look
better than reality because screen-I stays pretty much constant , so
the screen-V will not vary during the test.
>
> 3) And last....what is the correct bias voltage for this tube?

Correct bias is whatever it takes to produce virtually zero (<100µA) of
grid-I)  during maximum driving signal conditions.  However, ideally,
one should be able to adjust the drive, the screen-V and the grid-bias
V to achieve this since a ZSAC of 0.5A is needed to produce good
linearity.  Actual numbers are c. -340Vwith E-screen = 1400V.
/// note -- the rated screen potential of 1250V-max can be safely
ignored with this tube since the 8170/4cx5000A has the same innards as
a 4cx10,000D, whose screen is rated at 1500V.
>
> Thank you for your time. Please email me direct at kf6ikc at sbcglobal.net
>

-  cheerz, Stan

>  Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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