[Amps] Nat NCL2000

[m.ford]

----- Original Message ----- 
From: <HOWARDLYON at aol.com>
To: <amps at contesting.com>
Sent: Wednesday, February 22, 2006 11:34 AM
Subject: [Amps] Nat NCL2000


> Hi guys
> 
> Trying to renovate an old NCL2000.  Hadda shotgun the doubler  board.  The 
> caps were teenagers with pimples and whiteheads  everywhere.  The dividers were 
> all outta spec... 75k to 120k!~!~!  New  board is 12 pairs of 68uF/450V/105* 
> radials (about 11uF/5+kV) shunted by 12  100k/5W; new bypassed diode stacks; 
> Dale 25W heat-sinked limiter resistors; on a  3/16 XX phenolic board with 
> grommeted mounts and silvered test pin  connections.

I have rebuilt a number of these boards. I can't quite picture the configuration you describe.
Do you have  a photo?  Also you might want to reconsider using the Dale for a glitch
resistor. It will become a fragmentation grenade if given enough Joules to eat. Or at
least a double ended cannon.

> 
> Replaced the caps in the grid supplies.  Replaced and bypassed  alla the 
> diodes.  Replaced the smoked HV control relay.  Made the  wiring change to the two 
> 75k bleeders.

Add another one of the 75K to the stack. It will fit if you use shorter spacers. Keep the
same reason for the wiring change in mind. You may get a slight rise in the unloaded B+
but the heat reduction is significant. The 8122 is near its anode potential limit in the ncl
anyway so if you loose a tube from this it is ok to blame me. It is not ok however to
blame me if you use cheap little filter caps that can't handle the ripple.

> 
> The screen supply txstrs test OK, but the resistance measurements through  
> the network are all well beyond 10% out.  Anybody ever notice this?   Any ideas?

I think you mean the bias supply regulator? In any case, I would be surprised if any
of the original components were within original tolerances.
> 
> What is the ALC output?  My IC746 accepts 0 to -4V.  The circuit  looks like 
> it puts out much more than -4.  Attenuator time?

Remove the alc output jack and install another pot for the bias circuit. Wire it to allow
seperate bias adjustment of each tube. Key the beast with a dual foot switch so nobody
complains about the "kaawaak" sound from the relay.

Check out Rich Measures website for some other interesting things you can do.

Mike k1ern

 
> Thanx fellas.
> 
> Unca Billy
> N3TR
> 
>