> I've got a reasonably stock NCL-2000 (Hi Carl). I'm not looking for more
> power, and in fact, given my antenna location on a small lot, I probably
> should stay out of 10 meter, at least for any extensive use.
>
> My question is, I've found a source for NOS 8122's not matched, for a bit
> over $500/pair. The current ones work, but I'm looking to the future.
Ouch! I was selling matched and tested at 1200W NOS for $550-600 until I
ran out a few months ago.
>
> My options are:
> Gamble on the NOS tubes and hope they're close enough without being
> matched?
Unfortunately the grid voltage varies from around -25 to -40V and you need a
1V delta for good match. Modifying the bias circuit for individual
adjustments works but its still limited to about a 5-6V delta. Eimac
versions seem to be grouped a lot closer than RCA.
I assume I'd need to let these cook the O2 out for a day or so
> before real use.
It doesnt do anything useful for oxide coated filaments. The tube isnt known
to be a gasser either.
Adding individual bias circuit may be an option, but
> raises the cost.
See above. One pot, resistor and bypass cap..
> or
> Save the money and put it toward a newer mid range PA in that same 1 kw
> range (that I can buy spares for today) ($1400-$1700 + spares)
For the same power plus 160M and WARC find a LK-500ZC. I havent been able to
kill mine. Id stay away from the AL-1200 due to tube cost and a rumor (so
far) that the 3CX1200 series are being discontinued.
> or
> Actively work on retubing using something like the 4cx350A's, but
> understanding that I'm not a radio engineer, and I'll have to do a lot of
> study to make that happen (which I'm not adverse to). looks like the
> 350's
> use half the voltage @ 2x the current for the heater. Plate volts look
> right. new sockets from the looks of it. (maybe $350 for tubes plus
> unknown
> for sockets and other parts).
I converted a 2000 for George Badger at Svetlana years ago using their
4CX400A. Except for filaments (run them in series) and socket its plug and
play and much more rugged than the 8122. Better production tolerance
resulting in minimal bias tolerance range also. Others have gone with a
single 3CX/3CPX800A7 as its the same socket.
>
> There's also building something up from scratch using power mosfets based
> on
> the reference circuit diagrams, and then coming up with protection
> circuits
> and filtering. Probably beyond my current skill set, but it does interest
> me.
Ive zero interest in QRO SS and have enough spare tubes for all my amps that
will still be running after I reach room temperature.
Another good amp is an Alpha 76 3 holer with good or bad tubes as the prices
are way down. Run the good tubes until they die and then go with a pair of
3CPX800A7 pulls.
.
>
> thanks for the advice
> jim
Glad to pass along my wisdom....my #3 son wont take it (-:
Carl
_______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|