Hi Roger,
You wandered in several dimensions with that query.
For 2 KW out, I'd recommend going with a single tube, unless providence
brings something else, with sockets, your way. The obvious choice is an 8877.
Somewhat rarer, and typically less pricey surplus, are the old 4CX1500A, and
5CX1500A/B which are also good for 2 KW out but, are filament power hogs.
Covering 160-6 meters is a challenge. You might consider either switching to
a separate output network for 6 or... there is an old trick of inserting a
small (adjustable) coil, which will only marginally affect low band operation,
between the tube's plate and the tune capacitor. On 6M, the tube's output C
then becomes the input capacitor of output network and the low band plate
capacitor becomes the load cap with a separate small L coil from this point to
the 6M output connector. If the pi section of the low band output network is
simultaneously set to 160 Meters, it will have enough reactance (circa 5K ohms)
to be irrelevant. A separate plate choke will be necessary for 6 or... the
through the coil plate feed trick may be employed. See:
http://wc6w.50webs.com/wc6wamps/index.html?fr62.html
Finding the tube may not be the hardest part of your quest. The tank L's,
C's and bandswitch seem to be somewhat less available nowadays. And let's not
forget the matter of some largish power supply parts.
Transistors would be a whole 'nother can of worms. 2 KW reliably suggests 16
devices plus a bunch of splitters and combiners, a bank of output filtering, a
4 KW power supply, and if running into anything less than a perfect 50 ohms a
2KW rated tuner. It ends up being lots more stuff.
Now what was that about buying a commercial amp? :-) I believe that old
Henry 4K Ultras are going in the low $3K range; Not all that much when you
consider that those prices are in inflato-dollars. You'd only need to add a
few parts for 6 & 160 to meet your goal.
73 & Good evening,
Marv WC6W
http://wc6w.50webs.com/
--- On Sat, 7/26/08, Roger (K8RI) <sub1@rogerhalstead.com> wrote:
> From: Roger (K8RI) <sub1@rogerhalstead.com>
> Subject: [Amps] Building an Amp, Selecting a Tube
> To:
> Cc: "Amps" <amps@contesting.com>
> Date: Saturday, July 26, 2008, 7:20 PM
> I've looked over the present offerings for tubes
> (either one or two in
> parallel) to comfortably run the legal limit.
> There are a number of "out of production" Russian
> tubes that look
> attractive and are very inexpensive for a one off project
> complete with
> a back up tube although I'd like to keep the drive
> requirements down.
> There are also some fairly good tubes still in production
> that aren't
> all that cheap but some aren't all that bad. There are
> also the imports
> which are basically either Russian or Chinese. Although the
> history
> appears kinda poor for the Chinese tubes apparently they
> are getting
> better and some have done quite well.
>
> Of course there is also the 4 legged fuse approach and they
> are becoming
> both more rugged and less expensive, but the designs are
> not at all as
> simple as the old tube amps. Plus the protective circuitry
> can be quite
> elaborate. OTOH I do like the HL1.5-Kfx I have now. Of
> course I like
> my old, manual tune Alpha 76A as well.
>
> There is even a 4CX-1600B project available, but as the
> tubes are no
> longer manufactured and I doubt there were a great many
> sold to begin
> with, I'd want a spare tube. My potential goal is a
> legal limit,
> 6-meter amp that could run key down for hours.
>
> Near as I can tell (from what I've seen) the 4CX-1000
> is probably the
> most linear tube and it's still being manufactured and
> the price is "not
> all that bad" although I'd probably want to use a
> pair of them which
> would run about a grand just for the tubes plus their not
> so inexpensive
> sockets. Of course there are still both the 3CX and 4CX
> 800's as well
> which would cost a bit more for a pair of tubes but a whole
> lot less for
> the sockets. Both would easily run the legal limit on
> 6-meters with a
> bit of room to spare.
>
> Using current production tubes, or those solid state four
> legged fuses,
> building a well constructed amp will probably cost as much
> as going out
> and purchasing a new amp. I'm fussy so if I do build
> I expect to have
> the end result look like a commercial amp including the
> panel. IF I do
> go solid state I'll probably use current designs for
> the protective
> circuitry and plenty of good rugged transistors for a
> comfortable
> margin. Also, liquid cooled heat sinks are fairly simple.
> However as has
> been discussed, the delta T between the high power
> transistors and the
> heat sink can be a bit on the high side even with the best
> of heat
> transfer compounds. Basically I'd want one that could
> run 2KW out
> without self destructing to feel comfortable at the legal
> limit. Having
> HF through 6-meters would be very nice, but a separate amp
> for 6 is not
> out of the question. So I guess that is about as all
> inclusive as I
> can get.
>
> Any socially acceptable suggestions?
>
> 73
>
> Roger (K8RI)
>
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