How is the Dentron 1000b super cathode driven?
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On Friday, November 2, 2018, Alek Petkovic <vk6apk@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@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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