[Amps] Super Cathode Driven Tetrodes

Fri Nov 2 19:55:38 EDT 2018

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
> 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>  on behalf of Jim Thomson<jim.thom at telus.net>
> Sent: Tuesday, October 30, 2018 12:27 PM
> To: 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>
> To: Carl<km1h at jeremy.qozzy.com>, Jim Thomson<jim.thom at telus.net>,
> "amps at contesting.com"<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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