[Amps] Super Cathode Driven Tetrodes

Alek Petkovic vk6apk at bigpond.com
Sat Nov 3 02:34:05 EDT 2018 

In my circuit diagram, the control grid of each tube is tied to the cathode.

On 3/11/2018 7:55 AM, gudguyham at aol.com wrote:
> How is the Dentron 1000b super cathode driven?
>
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>
> On Friday, November 2, 2018, Alek Petkovic <vk6apk at bigpond.com> wrote:
>
>     Just as an aside, I have just finished refurbishing a Dentron
>     GLA-1000B
>     and I note that it is a Super Cathode design.
>
>     The Amp Supply LA-1000 and Ameritron AL-84 both use the same 6LQ6
>     family
>     sweep tubes. The LA-1000 is also a Super Gathode and the AL-84 is
>     straight Grounded Grid.
>
>     Cheers, Alek.
>     VK6APK
>
>     On 1/11/2018 9:59 AM, Jim Thomson wrote:
>     > ##  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 at contesting.com <mailto:amps at 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 at contesting.com
>     <mailto:amps-bounces at contesting.com>>  on behalf of Jim
>     Thomson<jim.thom at telus.net <mailto:jim.thom at telus.net>>
>     > Sent: Tuesday, October 30, 2018 12:27 PM
>     > To: amps at contesting.com <mailto:amps at contesting.com>
>     > Subject: [Amps] Super Cathode Driven Tetrodes
>     >
>     > Date: Sun, 28 Oct 2018 23:46:21 +0000
>     > From: "Fuqua, William"<wlfuqu00 at uky.edu <mailto:wlfuqu00 at uky.edu>>
>     > To: Carl<km1h at jeremy.qozzy.com <mailto:km1h at jeremy.qozzy.com>>,
>     Jim Thomson<jim.thom at telus.net <mailto:jim.thom at telus.net>>,
>     > "amps at contesting.com
>     <mailto:amps at contesting.com>"<amps at contesting.com
>     <mailto:amps at 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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