HF amp 4CX1000A help

Gerald Caouette

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Jul 25, 1995, 3:00:00 AM7/25/95

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Am looking to home build a single tube 4CX1000A 160 - 6 Meter
amplifier:
Any suggestions as to circuit details and reading material
would be apreciated
Most of the information I have found deals with triodes
or sweep tubes.
I am also intrested in building a 4-1000A 160 thru 10 meter
amp and want to compare the simalarities and advantages of
both tubes.
thanks in advance to all that respond
73
ar
sk
de ve6nap
gerald caouette.

Wes Stewart

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Jul 26, 1995, 3:00:00 AM7/26/95

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Gerald:

I can probably find other info given time, however, one article at hand is "An All Band
4CX1000A Super Cathode Diven Amplifier" in CQ MAgazine for April, 1970. This design did not
cover six meters, though. I'm not sure 160 - 6 coverage is too practical either. I'm not
saying it can't be done, I just think you're asking for heartburn.

If you want a copy of the article, please send your mail address.

Regards, Wes -- N7WS

W8JI Tom

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Jul 26, 1995, 3:00:00 AM7/26/95

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ve6...@cronus.oanet.com (Gerald Caouette) wrote:
>Am looking to home build a single tube 4CX1000A 160 - 6 Meter
>amplifier: Any suggestions as to circuit details and reading material
>would be apreciated Most of the information I have found deals with
>triodes or sweep tubes. I am also intrested in building a 4-1000A 160
>thru 10 meter amp and want to compare the simalarities and
>advantages of both tubes. thanks in advance to all that respond

Hi Gerald,

The 4CX1000A should work well on six meters, but I am afraid you will
run into network and choke problems on one end (160) or the other (6).
It is almost impossible to get a good plate choke from 160 through ten,
let alone trying to include six! Plus the stray capacitances and lead
lengths will kill performance on six unless you are very very careful.

There is as much in-correct as correct advice in amateur publications on
amplifiers. I would get a copy of Eimacs publication "The Care and
Feeding of Power Grid tubes" and read it carefully. I would also avoid
witchcraft and voo-doo circuits.

For the 4CX1000 I would recommend copying Collins 30S1 circuit.
Screen regulation, control grid regulation, and current protection is
absolutely necessary if you want a good clean long lasting amplifier.

The Collins circuit was "borrowed" and published as a "Super Cathode
Driven" amplifier, but be aware the circuit ONLY WORKS with a class
AB1 tetrode or pentode, it will NOT perform correctly with triodes of
ANY class, or tubes that draw ANY amount of control grid current such
as 4-1000A or 4-400A tubes.

Used correctly, the Collins circuit reduces chances of damaging the grid
and improves linearity. Used in incorrect applications it lowers
linearity,
stability, and gain flatness. NEVER use the "Super Cathode" circuit with
ANY triode or in any amplifier that produces control grid current!!!!!!

A second method I use involves a non-inductive (be SURE it is really
non-inductive) resistor from the grid to ground and normal screen and
bias voltages and connections. The value of the control grid resistor for
class AB1 using this grid swamping resistor is given by the bias voltage
squared over two times the driver power. The screen grid MUST be
grounded with a very low HF through VHF impedance connection or the
tube will be unstable. If you ground the screen correctly there is usually

no need for any parasitic suppression device with this tube.

The 4-1000A is a generally unstable tube because of the long internal
grid connections, but is also a much more rugged tube in terms of
control grid problems. I would use the 4-1000 in conventional grounded
grid with ALL grids tied directly to the chassis with VERY short heavy
leads. You should use a special parasitic suppressor with this tube. It is

usually be a real pain to stabilize because it trys to oscillate at low
VHF
frequencies.

I would use a parallel resonant parasitic supressor tuned to the 60 to 80
MHz range, or a series parallel circuit consisting of a series 100 ohm R
and 115 nanohenry inductance, and a 27 picofarad capacitor placed
across a 4 turn 1/2 inch diameter #10 copper coil at the anode terminal
of the 4-1000A tube.

That will give complete supression without unwanted heat or
performance degradation on 15 and ten meters.

Most conventional carbon and metal film resistors have considerable
internal inductance that renders them useless as a suppressor resistor in
most applications. Either cut a sample component open and look at it or
measure it on an impedance bridge (the MFJ-259 works great for this).
If the resistance element is wound in a spiral the thing is usless for
suppression. As far as I know only Allen Bradly still makes non-
inductive 2 watt carbons, I can source them if you have trouble. Even
the small grey metal films are too inductive for some suppression
applications.

Good luck with your project. 73 Tom W8JI

Douglas E. Marsh

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Jul 29, 1995, 3:00:00 AM7/29/95

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> Good luck and let me know you you get on. If you want (or anyone else
wants), > I could e-mail a list of 2m ish 1000A ish amp references, after I've
found at > home.
>
>
> dave kirkby G8WRB.

Dave;
I for one would be interested in you references. I would also be
interested in the feasability of Homebrewing VHF amps. I realize that the
voltages are very high and although I have been messing around with building I
have yet to work with such voltages.
I would appreciate it if someone could give me the general idea of the
scope of such a project. Are components readily available? How do I avoid
blowing up EXPENSIVE power tubes?
You know little details like that!

73 de N8TUT

Doug :-{o

-------------------------.-------------.-------------.-------------------------

Conrad Farlow

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Jul 30, 1995, 3:00:00 AM7/30/95

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For what its worth I sucessfully built the 4cx1000a 2m pa from the arrl
handbook.The use of grounded screen is a very good idea,not only from
the view point of stability but also a good base is hard to find or
very expensive.You can probably find one with a damaged screen bypass
cap and fabricate your own base.I think it will be very tricky to get a
bandspread(term???) of 160-6m.There was a design in the arrl handbook
for a 4cx1000 on 6m I seem to remember that the output coils
inductance was varied by compression and expansion.I think its a
very good idea and saves on a high voltage variable cap.The nice
thing about the 4cx1000 is the low drive requirements.I can get well
over 1.8kw with 25 watts of drive into a dummy load of course on 2m.I
dread to think what gain you could achive on 6m.This gain makes for
low tolerance of feedback paths so careful construction is necessary.
If it were me I would use the 4cx1000a on 6m and get a big triode for
the hf amp.
73 de Conrad G0RUZ
email con...@g0ruz.demon.co.ukPacket
Radio G0RUZ @ GB7WRG.#19.GBR.EU

John Dilks

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Aug 3, 1995, 3:00:00 AM8/3/95

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Gerald Caouette asks:

-> Am looking to home build a single tube 4CX1000A 160 - 6 Meter
-> amplifier:

Gerald,
Your amp is in some of the older ARRL Handbooks, as I remember. I
have a number of them. If you don't get help from others, send me some
mail and I'll spend some time looking through them and I'll photocopy
the article for you. But you might be better-off asking around your
area for some of the older copies from your friends. You need to read
more about amps if you are planning on building one. There is much to
learn! ....>>> Be Careful! <<<....

73', John Dilks, K2TQN::::: john....@academia.com