The HV power supply isn't half wave, it's a full-wave voltage doubler.
100uF caps should be fine, the originals in mine were 80uF and have
never been replaced, still fine in 2010 (with different owner).
WB2WIK/6
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
On Behalf Of jim feldman
Sent: Wednesday, January 13, 2010 10:51 AM
To: amps@contesting.com
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?
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)
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.
Thanks
jim
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