Thanx Mike. Decided to repost in case someone else wants to know about the
caps et al.
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?
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.
The new board is 3/16 XX bakelite. I drilled and chamfered the holes for 1
/4 inch grommets. These mount the cans and shunts. In the chassis, the
resistors are on the top of the board (at a higher elevation than) and the
caps
are facing the screening of the Chassis enclosure.
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. (Sent directly, not posted to the group.)
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?
>
> 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????
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
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