My advice is:
Don't convert from 8122 to 4CX250b.
I am aware that many get 1kw out of these, but the signal is not linear.
The anode voltage will be far beyond the max spec for the 4cx250b.
In the long run, reduced reliability will easily offset the price
difference.
The 2x8122 is designed to run 1kw output, see RCA/Burle dataseets, the
2x4cx250b is not.
73 de LA6MV
Helge
-----Original Message-----
From: Steve Katz [mailto:stevek@jmr.com]
Sent: 29. september 2003 16:46
To: 've7avv@shaw.ca'; amps@contesting.com
Subject: RE: [BULK] - [Amps] NCL 2000?
It's a very pretty amplifier that is, of course, also quite old, c. 1966 or
so. As such, if it has its original filter capacitors they should be
replaced, along with their equalizing resistors. The 8122 replacement cost
is scary, but many have converted to other tubes successfully. One recent
conversion we did was to create a 6m monoband amp from an NCL2000 and
because the tubes were weak, the final conversion involved replacing them,
and their sockets, with 4CX250Bs -- still puts out a kW on 50 MHz, with much
more available (and cheaper!) tubes. Small power supply mods are required
for that, but they're easy and inexpensive. The original circuit has
untuned input, swamped by a resistor bank. One drawback to most amps of
this era, including the NCL2000, is no 160m coverage. -WB2WIK/6
> I'm looking for comments (pro and con) regarding the NCL 2000 amp. I
> have an opportunity to buy one dirt cheap and aside from the cost of the
> 8122 tube, I'm wondering if there is anything else I should be aware of
> with this box?
>
> 73 de Paul, VE7AVV
> StoneyGround Station
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