4CX1000A in grounded grid ( 4CX1000 GG )

[Opcom]

Has anyone seen or built an amplifier using a 4CX1000 in a grounded grid circuit?
Including one where the control grid (zero dissipation) is connected to the cathode, and the screen only is what is grounded?

[WD8BIL]

Give this a read, OP!

GG Basics

[WA1GFZ]

Copy Collins 30S1 or grid drive it. This tube has no real grid dissipation so easy to hurt it.

[W2VW]

The Orr Radio Handbook which is referred to as the West Coast Handbook had a grounded screen linear final project. It's not in the 1972 one. Maybe a few years later.

[Opcom]

Yeah that's just going to make it worse, grounding the screen on top of having to supply the other voltages. A friend wants me to build him an amp around a tube he has, but I don't have the time really to add another project and if I have to add bias and screen supplies and monitoring, etc, it'll never get done.. I may try to steer him towards a cheaper non-$500 tube, triode, or easier to find a socket for anyway. Or I could give -him- the 30S-1 manual or something simpler like the NCL-2000 manual and get him to do most all the assembly.

I'm in luck at the moment tho because in the dark warehouse he thought his plate iron said 3300V/1A, but in the light of day it is a 3300V/1KVA so that takes care of that.

[WQ9E]

Patrick,

If you are trying to go with a quick build for a tetrode amp I suggest you consider the G3SEK tetrode boards.  They provide a nice and simple solution for the necessary voltages, protection, and switching.

As others have stated, a lot of tetrodes are not suited for use in GG service.

http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-1.htm

[W2VW]

Sounds like a job for the Russian military.

Yeah that's just going to make it worse, grounding the screen on top of having to supply the other voltages. A friend wants me to build him an amp around a tube he has, but I don't have the time really to add another project and if I have to add bias and screen supplies and monitoring, etc, it'll never get done.. I may try to steer him towards a cheaper non-$500 tube, triode, or easier to find a socket for anyway. Or I could give -him- the 30S-1 manual or something simpler like the NCL-2000 manual and get him to do most all the assembly.

I'm in luck at the moment tho because in the dark warehouse he thought his plate iron said 3300V/1A, but in the light of day it is a 3300V/1KVA so that takes care of that.

[KM1H]

Yeah, a GU-81M where you can watch it while tuning and still not hurt anything with a goof.

I wouldnt trust someone with a 4CX1000A unless it had an idiot proof grid and screen trip. A 4CX1500B is a wee bit better in the grid survivability.

At least the NCL-2000 8122's can handle substantial grid current without damage.

Carl

[Opcom]

Thanks for the tip on the G3SEK tetrode boards. At this point, I'll ask him to do all the mechanical stuff and I will just supervise the tricky parts and insist on the tetrode board. that will save my time and he'll learn a lot. He repaires electroplaters for a living, big ones too, like 3000-6000A. I agree after studying the tube it will be easy to blow up no matter what. I tried to suggest something esle but he wants to use what he has.

Patrick

[WQ9E]

Patrick,

There is nothing very complicated about the tetrode boards but make sure you oversee his calculation of the transformer and the various resistors for the screen supply.  They have greatly improved the instructions since I built mine back around 2001 or so and now it is more of a fill in the blank exercise.

Also keep in mind that you can easily add additional trip protection (such as high swr) using the control circuits built into the board.  I added high SWR trip to mine.

I used a time delay relay to keep the blower running for 3 minutes after I shut off the amp.  There is a built in warm-up delay timer to protect the tube.

[KG6UTS]

July 63 QST had plans for a 4-1000A gg linear on page 29. A few years ago I worked on one of those built by Cliff N6ZU. Cliff was featured in 2007 Electric Radio 218/219 in an article about his amps. The one I was working on sure looked like those in the article so I contacted N6ZU and he said the amp was one of his early ones. Anyway, I have a .pdf of the QST article if anybody wants it and it might be on the QST website too. Cliff's amp was a great piece of home brew.

EdZ KG6UTS
KG6UTS@AMSAT.ORG

[Opcom]

The 4-1000 is a whole other animal and although it is much larger for the same power, i'd take one of those any time over a 4CX1000.

[KM1H]

4CX1000A = 1680W out tops and that is maxed out at 3000V. At the same voltage a 4-1000A is around 1300W PEP and its just starting to wake up. Run it with 4-6KV and up to 3-4KW is easy.

Tube life is a lot longer with the glass jug also and was a favorite in BCB TX's up to 5KW out on AM with a pair.

Carl

[WA1GFZ]

Anybody remember the 3-1000Z finals at W1AW built by W6SAI?
That was a thing of beauty seeing them in the racks ready to kick butt.
I remember them lined up on a shelf in the basement when they were replaced by the Harris rigs. This was before my cousin was running the station. He suspects they evaporated. I told him that was their biggest mistake taking them out of service. They could have easily swapped over to newer tubes like 8877s or 3CX3000s

[W2PFY]

Maybe they were sold on Ebay? The reason I suggest this is because I seen the mono bander 20 meter 450TH amplifier on ebay with documentation.It was described in the Fourteenth addition, page 584.

I got outbid and never seen another piece of his equipment on line.

[W2VW]

Times have changed a lot when sourcing QRO stuff.

Goodbye screwing with 4-1000 parasitic supressor schemes. Good riddance.

The 4-1000 is a whole other animal and although it is much larger for the same power, i'd take one of those any time over a 4CX1000.

[KM1H]

If you understand amp design its a minor issue that is easily solved. Learn on the first one and after that its easy.

[W2VW]

If you understand amp design its a minor issue that is easily solved. Learn on the first one and after that its easy.

I have the concept down 

Problem is never building the same thing twice being cheap.

I'll take an external anode any day. Nothing is as cute as a few 4-1000s blushing but I'm over the visual effects at this stage.

[WA1GFZ]

W1AW 3-1000A rigs evaporated long before epay

[KM1H]

Im in my second childhood and have returned to my roots, old glass bottles, just like sucking on a nipple

What I really want is a couple of 750T or larger ones

I also have plenty of that ceramic stuff around here for the DX and VHF to microwave side of the basement.
Lots of blower noise and no photogenics.

[Bill, KD0HG]

I once built a leenear using a pair of 4CX1500Bs. (Sorry I ever sold it).

In any case, it was grounded cathode but with an untuned, resistive input. A 100-watt 50 ohm load directly driving the 4CX1500 grids via a capacitor.  5 KW out with 100 watts of drive.

[Opcom]

I like glass triodes and glass tubes in general because you can glance at the tube and get an idea what is going on with it regardless of what the tube is being used for.

The 3-1000 is always shown running a rather low plate voltage when used as a ham RF linear amplifier. Maybe it's wrong but it seems in poor taste to always present, in the ARRL books, amplifiers that can just -barely- make the maximum amount of power.

Check out the push pull class B audio data @ 5KV for it.

[WQ9E]

I think the ARRL (and Eimac) were probably really emphasizing the zero bias capability of the 3-1000Z and it will need to have operating bias at higher plate voltage to stay within rated dissipation.

I imagine the 3-1000Z would be a very expensive tube to find now, the 3CX1200 isn't as pretty but a lot more practical.

[WA1HZK]

I had one here for a while. Tina just took it apart. It was running with both grids grounded and also as a G2DAF? I think that was his call design. Ran good no issues.
It may come back as plate modulated some day. The problem with those tubes is that they used to be cheap and are now getting hard to find. If I had a 3-1000 amp with no tube I would drop a 4-1000 in and it would probably run just fine. But if you toast it, kinda hard to replace.
Keith
WA1HZK

[KM1H]

Have you checked 3CX1200 prices lately Roger, any of the 3 versions?

Carl