RadioBanter - View Single Post

December 17th 05, 04:15 AM posted to rec.radio.amateur.homebrew

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.