Hi Dick,
As a member of the original NCL-2000 design team and an owner of 3
prototypes (one on 6M since 1964) I offer the following:
Take a very careful look at the filter caps. If the amp is original they
will be 80MF/450V , fairly long and with a black jacket. The National
Part # was C-51447-1 and should be marked on the jacket. The last line
will be the date code...6415, etc.
The PS board has 2 sides, remove the 4 mounting screws to access the
other half of the filters. It is a pain but you should also check the 50K
equalizing resistors across all 8 caps. They should be within 5% .
Another thing you can do is to measure the voltage drop across each
cap...there should be a 5% total deviation. If you turn the amp up on the
xfmr end, twist the PS board out and be careful you can do all the
trouble shooting you need without removing wires.
The NCL-2000 has 120/240VAC selection on the rear panel. If you do not
have a Variac for 240 you can wire for 240 (actually 110/220 back then)
and plug in to 120V for initial smoke test.
Before doing anything you should remove the 8122's, open the grid
compartment cover and check the condx of the 100 Ohm screen resistors.
The original NCL used 20% tolerance 1/2W carbons....you can easily see
any changes or blown resistors.
A blown resistor usually signifies a screen to plate short.
The relays are all 12VAC which becomes a problem with some exciters. Also
the plate relay is really a piece of junk ! It arced from day one. I
replace with a 12VDC relay with better insulation to the frame....many
will fit right in place....I get the DC by a 1/2 wave rectifier and a
470MF cap....no rocket science needed; just bleed the DC with roughly 1K
1W otherwise it will never release!
8122's are still in production by Burle who bought the old RCA line.
Others are Eimac 8122W's and Amperex. The Mil-Spec Eimacs are bullet
proof....I have a pair here I use when converting the NCL to 6M and they
have survived all the abuse I can give them while taming parasitics.
I have all field bulletins, etc and may be able to help you with
problems...BTW, I would need the serial # off the back panel which is
stamped in black ink.
73 Carl KM1H
Amplifier Repair and 6M Conversions Our Specialty
National Radio 1963-69 and part of the NCL-2000 design team
On Fri, 11 Sep 1998 09:48:45 -0500 Richard Carroll
<w0ex@scan.missouri.org> writes:
>
>I have just acquired a very nice old
>National NCL2000 amp (along
>with the matching NCX5 transciever &
>NCX-A supply ) that
>hasn't been turned on in about 20 years.
>I intend to bring it up
>slowly to reform and avoid shock to the
>old power supply electrolytics.
>I have a 120vac variac, but none for
>220, and I believe this should
>work out OK, but what are the "gotchas"
>involved? I feel that I should
>remove the tubes as a precaution against
>any possible damaging flashover.
>Any suggestions from those who are
>familar with this amp? Also
>any loose 8122's around and available?
>I'll want some spares if I keep it.
>
>Dick W0EX
>
>
>--
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>
>
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