Any 3CXPX1500A7 or Y-xxx medical pull at close to full output. Reasonably
priced so you can buy a spare or two.
At your criteria I cant see any other tube that comes close that will still
be around 10 years down the road (my prediction) and is affordable, reliable
and an easy build.
Id rather build a no compromise MF-HF amp that covers (or makes expansion
provision) all current and potential new bands (600 and 60M) and leave 6 to
a monobander or 6 & 2.
Carl
KM1H
----- Original Message -----
From: "Roger (K8RI)" <sub1@rogerhalstead.com>
Cc: "Amps" <amps@contesting.com>
Sent: Saturday, July 26, 2008 10:20 PM
Subject: [Amps] Building an Amp, Selecting a Tube
> 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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