## That was back in the 70s and early 80s that I know was last done in a high
mu config.
I mentioned the high Mu config to Reid Brandon at Eimac, 10-12 years ago,
and he told me it was very feasible,
and done quite often. Gain is down a bit from a high Mu triode..and also imd
is not as good, but the
4x5 had acceptable imd up to 7.5 kw pep out..into a 50 ohm load. What I
dont remember, is what the input Z is.
High mu config , of course is when the screen grid... and control grid are
both bonded directly to the chassis. Tube
is operated like a high Mu triode.
## One method of determining input Z, is to 1st guestimate the input Z...
and build a low Q PI input for one band, say 40m.
With drive applied, both input caps are tweaked for 1:1 swr. Then everything
is shut off. 100 ohm pot temp wired between cathode
and chassis..and tube left in socket. MFJ-259 on input.. and pot tweaked for
1:1 swr. Pot then measured with a DVM...and that
value measure is the actual input Z. At that point, knowing the real input
Z, correct valued, and optimized low Q PI tuned inputs
can quickly be designed for each band. I use the superb GM3SEK PI spread
sheet for designing both the PI tuned inputs.
and also the PI / PI-L high powered tank circuits. One caveat /
limitation when using the spreadsheet for a tuned input is....
it will handle any Z to Z transformation combo you want.. EXCEPT when the 2
x Z’s are identical ! IE: IF tube Z is 50 ohms, you can
not enter 50 to 50 ohms .... or say 70-70 ohms. The software bombs and
displays a bunch of ####s. The best you can do is to enter
50 to 49 ohms...... or 49 to 50 ohms.... then it works fine.
Jim VE7RF
From: Fuqua, William
Sent: Wednesday, October 31, 2018 4:22 PM
To: Jim Thomson ; amps@contesting.com
Subject: Re: [Amps] Super Cathode Driven Tetrodes
Do you know anyone that has had first hand experience in running 4CX5000
tubes in conventional grounded grid configuration? I have some that I would
like to try perhaps. They have 75Watt control grid dissipation and 250 Watt
screen grid dissipation.
73
Bill wa4lav
--------------------------------------------------------------------------------
From: Amps <amps-bounces@contesting.com> on behalf of Jim Thomson
<jim.thom@telus.net>
Sent: Tuesday, October 30, 2018 12:27 PM
To: amps@contesting.com
Subject: [Amps] Super Cathode Driven Tetrodes
Date: Sun, 28 Oct 2018 23:46:21 +0000
From: "Fuqua, William" <wlfuqu00@uky.edu>
To: Carl <km1h@jeremy.qozzy.com>, Jim Thomson <jim.thom@telus.net>,
"amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] Super Cathode Driven Tetrodes
<Ok,
< Now that this discussion has gone on for some time, and everyone has had a
opportunity to read various articles, here is the question.
<Can anyone give me a reason why a cathode driven tetrode with the control grid
connected directly to
<the cathode be unstable. The screen grid is connected directly to ground. Low
mu grounded grid configuration.
<73
<Bill wa4lav
## Its rock stable, based on data from the 70s, from nearby hams who used
that config. But that was a 4CX-1000
in both cases. 160 w of drive for 1200 w pep out on ssb / cw..... = power
gain of just 7.5..... = 8.75 db.
The super cathode driven config was only used on tubes that had virtually no
control grid dissipation, like 4CX-1000, and 4CX-1500B etc.
Tubes like 4CX-5000, and bigger, can have both their control grid and screen
grid bonded to chassis.. and run like a high mu triode.... just like a 4-400,
or 4-1000.
Jim VE7RF
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