----- Original Message -----
From: "jim feldman" <mtnredhed@gmail.com>
To: <amps@contesting.com>
Sent: Wednesday, January 13, 2010 1:50 PM
Subject: [Amps] NCL-2000 mods
> I've been through the archives at some length, so I'm looking more for
> confirmation of what I'm about to do.
>
> I recently acquired a fairly "virginal" 71 series NCL-2000. A little
> dusty
> on the deck, but no rust. Looks like 1 or 2 of the relays were replaced
> over time. No obvious arcing or other damage. 8122 have been tested
> under
> load to be fairly good (1300w PEP on 80M ssb). My goal is to only run
> this
> on the designed bands (80-10) and probably mostly on the CW lower power
> setting. I'm going to drive it with a Kenwood TS-440 which should be
> able
> to operate the transmit relay and read ALC. I want to do the following:
> 1. recap the HV supply - caps on order and I'm checking the bleed
> resistors
> to make sure they're in spec. The highest value axial lead 450v cap I
> could
> find available was 100uF. I've seen higher recommended, but the only
> higher
> values were in radial or snap in. I know this is a noob question, but why
> is
> the HV supply only half wave rectified?
The 100uF Sprague Atom wont clear the chassis, its too wide. Get the 80uF
while you can as Atoms are being discontinued. Use 100K 3W MOX resistors for
equalizers to minimize heat. The amp already has a seperate bleeder.
> 2. Use Rich Measures' series zener mod to provide regulated 390v to the
> screens from the HV supply. Seems like a pretty safe mod. I know there
> are
> more advanced methods, but this seems simple, noob proof and easy to back
> out. (plus fairly cheap to build)
Yuk. Not very safe, smart, plus it can hurt the IMD. Use the G3SEK or other
SS regulator.
> 3. This part seems to be a bit more controversial. I'd like to add the
> resistors (RM's design) to lift the cathodes off ground and provide a
> little
> neg feedback. There do seem to be some issues with the type of resistor
> and
> the installation technique. Any hints here would be greatly appreciated
> as
> there appears to be a high risk for parasitic vhf generation.
More bad info from voodoo science land and yes it creates a parasitic
nightmare on 10-15M requiring a screen ring bypass from Johnson or others.
End result is no improvement.
Carl
KM1H
National Radio 1963-69
Member of NCL-2000 Design Team
>
> Thanks
> jim
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