Hi Helge,
Re: Your 4CX250B comments.
I've had the same set of Eimac 7203/4CX250Bs in my two meter amplifier since
1981. Run it with Ep = 2500V, Eg2 = 350V, lots of air, and 1 kW PEP output
power for, oh, about 10,000 hours so far -- same tubes, still generating 1
kW PEP output at 144 MHz. Ip = 615mA, Eff = 65%, Pdiss = 538W, which is
7.6% above continuous rating per the data sheet. With proper loading, Ig1
<10 mApk and Ig2 = about "zero," plus or a minus a few mA.
The NCL2000, as you know, has a two-position HV switch. In the low
position, Ep = about 1800V, for the faint of heart.
I think substituting a pair of 8874s for the 8122s and converting the amp to
GG would be a far better idea, but 8874s are expensive, too. Never tried
the Russian tetrodes (yet), possibly a far better sub, especially for cost.
-WB2WIK/6
"Success is the ability to go from failure to failure with no loss of
enthusiasm." -Winston Churchill
> -----Original Message-----
> From: Skram, Helge (MED) [SMTP:helge.skram@med.ge.com]
> Sent: Tuesday, September 30, 2003 6:31 AM
> To: Steve Katz; 've7avv@shaw.ca'; amps@contesting.com
> Subject: RE: [BULK] - [Amps] NCL 2000?
>
> 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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> >
> >
> >
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