wrote:
If everything works out this weekend I should have about 10w or so to
drive into a linear. My friend here in town thinks I should buy used
Dentron Clipperton or Heathkit. I don't think 10watts would do either
justice. If 10w would give me a KW out with a commercial unit I would
consider buying a good used unit.

Plan bravo is to build. I would have to do tubes in keeping with the
theme of that side of the shack. CW, AM, & SSB are all modes that I
would operate. I only need to operate 160m - 40m. I am experienced
transistor engineer and my early schooling was in tubes , so not beyond
my reach for this type of a project. I have plenty of other homebrew
projects to keep me busy if this one gets scratched.

I need help picking a topology and a tube set. Price and likelyhood of
getting the thing working are two top runners. From the 1965 ARRL
Handbook I see a few different tubes that might qualify. A Pair of 813
in parallel, 3-400Z, 3-1000Z. I am soliciting some opinions on the
topology. Again, all I got is about 10w am going into. I would like
to do a kw or so pep. I am not looking to buy any parts at this time,
so not looking for any 'sales calls'. I need comments like - look at
this tube with this plate voltage kinda thing. Or try driving this toob
with a such and such to get a kw out. I would like to keep the design
required to a minimum and would consider some 'reverse engineering' a
plus at this point. If I can get most of the design out of an old ARRL
handbook then that would please me.

73
Bob
N9NEO

As others have pointed out you will need a tetrode amp to get
20db of gain in one stage. The old warhorse 4cx1000a will do it,
but this is an expensive tube with an expensive socket to match!

Look for a Svetlana 4cx800 tube. The sockets for this are not
too costly and the tube itself is in the $100-$150 range. A single
4cx800 will get you close to the legal limit. You can drive this tube
as a conventional grid driven with tuned input, or use an impedance
matching transformer with a 450 ohm swamping resistor.
Yet another way is to run the tube cathode driven, but with normal
grid bias and screen voltage, both grids bypassed to ground for rf.
I'm not sure how much drive will be required in the cathode driven
mode, but if operated in AB1 it will be much less than a conventional
grounded grid circuit.

Ken Scharf wrote:
A single 4cx800 will get you close to the legal limit.

That's being over-ambitious. The manufacturer's data (Svetlana) says
that a single 4CX800A "will conservatively produce 750 watts PEP SSB,
and 750 watts Key Down CW in any of the three modes: grid-driven,
grid-driven passive input, and cathode-driven."
http://www.g8wrb.org/data/Svetlana/pdf/4CX800A.pdf

You can certainly screw more power from the tube, but intermodulation
levels will rise rapidly. When selecting a tube, a good rule of thumb is
to expect an RF output equal to the tube's anode dissipation.

If the original aim was for something "in the region of" a kilowatt, it
would be well worth considering a single 4CX800 at slightly reduced
output.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ok, thanks Ken & Ian & others. My post has spawned just the type of
comments that I had hoped for.

Ian, I've been over to Tom's tubes and I see you have boards over
there. If I do the tetrode I will probably pick up a kit to help out.
I don't like to re-invent unless there is a clear-cut advantage to
doing another way. I'm up in the air over 2 stages or the Tetrode. I
think the tetrode is probably going to win. I've posed the question to
some AM types on AM Fone to see what they say.

Ok, thanks Ken & Ian & others. My post has spawned just the type of
comments that I had hoped for.

Ian, I've been over to Tom's tubes and I see you have boards over
there. If I do the tetrode I will probably pick up a kit to help out.
I don't like to re-invent unless there is a clear-cut advantage to
doing another way.

Ah, I didn't realise you were a neighbor of Tom's. (As I hope you
understand, I was writing with the 'In Practice' hat on, and definitely
wasn't trying to sell you anything.)

I'm up in the air over 2 stages or the Tetrode. I
think the tetrode is probably going to win. I've posed the question to
some AM types on AM Fone to see what they say.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:
Ken Scharf wrote:

A single 4cx800 will get you close to the legal limit.


That's being over-ambitious. The manufacturer's data (Svetlana) says
that a single 4CX800A "will conservatively produce 750 watts PEP SSB,
and 750 watts Key Down CW in any of the three modes: grid-driven,
grid-driven passive input, and cathode-driven."
http://www.g8wrb.org/data/Svetlana/pdf/4CX800A.pdf

You can certainly screw more power from the tube, but intermodulation
levels will rise rapidly. When selecting a tube, a good rule of thumb is
to expect an RF output equal to the tube's anode dissipation.

If the original aim was for something "in the region of" a kilowatt, it
would be well worth considering a single 4CX800 at slightly reduced output.



I didn't have the data sheet in front of me, but I just assumed that
with a plate rating of 800w it would max out near 1200w out.
The 3cx800 tube will put out this much and there are single tube
amps using this bottle that will do that. Guess the 4cx800 is a
bit short on the plate voltage or max cathode current rating to
make it to 1200w.

Well you could use a pair of 4cx800's to get to 1500w out if that
is your goal. A pair of these are STILL cheaper than a single
4cx1000a or 8877 (especially with the cost of the sockets
figured in).

Hi Ken,

1500w was the target, but I see it's not so easy a target to hit on a
budget. I just did an inventory of shack and realized that I spent a
whole bunch of cash over three years just getting back into radio. A
couple of boatanchors, high performance receivers and some decent test
gear have kept the accounts payable department busy here in MA. (The
N9 call followed me east after college) Wife and I have other interests
that also run on cash, so I can tone down the amplifier performance a
bit no problem. I can be happy with a smaller amplifier and maybe some
time down the road build a bigger beast. 100w-200w of carrier on
160-40 would suit me fine right now. I can build giant multi-kilowatt
transmitters using mosfets if I want to, but the tube thing has a
certain appeal to me now. I got my first class commercial ticket over
thirty years ago but never did much with the hollow state. I'm having
a blast now with the BAs.

Thanks for the help (to all). I'll be asking lots of questions as the
design goes forward.

73
Bob
N9NEO