----- Original Message -----
From: <HOWARDLYON@aol.com>
To: <k1ern@direcway.com>
Sent: Friday, February 24, 2006 2:42 PM
Subject: Re: [Amps] Nat NCL2000
> In a message dated 02/24/06 13:28:20 Eastern Standard Time,
> k1ern@direcway.com writes:
>
>
>> 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.
> What caps did ya use?
(CDE WBR100-450 or MALLORY TC80)
>
> The caps (DigiKey P11692) rated at 0.76Aripple each (1.5A para) and ESRs at
> 1.950. The only way I could figure to replace the old monsters...... and
> still stay clear of the chassis. As is, the tops of the cans will be about
> a
> quarter inch from the bottom screening. Glad they have PVC caps under the
> wrappers.
>
>
> 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.
> See attached JPGs.
>
> The Dales are 10ohm/25W in series with each diode stack with a common connex
> to the lower txfmr lead on the schematic Surge protection for the diodes.
> About an 8 V drop and 6 or 7W diss. Thot the 25W shud gimme a bit of
> comfort. Inna glitch, they oughta hold for a second or so 'til the overload
> trips.
> I hope.
>
> The diodes are two sets of three 1000V/6A R6-body barrels, shunted with
> .01/1000V caps. Should I have used 4? Some say forgeddabout the caps. The
> weakest link, and all that good folderol. Wotz ur take on it?
(I use K2AW HV6-1 modules in place of the oem solitrons)
>
>
>
>>
>> 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.
> Nah... won't bust ur jewels. Yeah I read the tube sheets. Know what ya
> mean. Nudge nudge. Wink wink. Was even wondering about surge protecting
> the
> 240 primary leads. Lower the turn on, and dump the HV down a tad.
>
>
>
>>
>> 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.
> Yeah... answering too many mails too fast. The grid supply. I'm blushing.
> :-|
>
>
>>
>> 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.
> Ummmm..... dat don't sound kosher. KAAWAK????
(The changeover relay is loud. By using a dual footswitch you key the amp first,
before the exciter and the sound of the relay is lost on everyone but you)
>
>
>
> Check out Rich Measures website for some other interesting things you can do.
> Righto righto. Been there. Got it printed and in the notebook... the
> resistive divider supply (old-thymey) to replace the (super-modern)
> electronic
> auto bias.
>
>
>
> Mike k1ern
> Thanx Mike. Good to have you guys for input ahead of time. Imma virgin, be
> gentle with me.
>
> ;-))
>
> Unca Billy
> N3TR
>
Mike k1ern
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