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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