To build or not to build
 

Hey Bill you got some really good points there. (Yes, 6146)

I figured a homebrew Amplifier project could be a costly undertaking.
I got over $500 into the HX-50 with the cost of the unit and parts to
get it running. I had about 80 hours into a Knight T-150 to get it
working correctly. Was my first rig and I called it a learning
experience to ease the pain. The reason we play with these radios is
because we like to rather than to make any money at it.

I've got a few big mosfet projects in front of the amplifier, so not in
any hurry. (I can do a full PEP setup with a half dozen fets for about
200 bucks.) I'll do some more poking around and see what I come up
with. Project may in fact become a reduced output amplifier.

Thanks everybody for comments. I will mull over and figure this all
out as other projects get finished.

73
Bob
N9NEO

To build or not to build
 

To build or not to build
 

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

To build or not to build
 

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.

To build or not to build
 

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

To build or not to build
 

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).

To build or not to build
 

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