NAD: 1976 Marshall JMP 2203 with Superlead cosmetics

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demonufo
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Re: NAD: 1976 Marshall JMP 2203 with Superlead cosmetics

Post by demonufo » Sat Feb 23, 2013 2:33 pm

Absolutely no point changing a cathode resistor for a carbon composite IMO. I wouldn't bother with CC's on these circuits anyway, but I doubt you'd notice much difference between types on the cathode.

Those green caps are really fragile. I only managed to save two out of five that I removed from my old board. Closest replacement for these would probably be Vishay MKT368, but they're a bright orange, like orange drops, albeit smaller and closer to the required lead spacing, I think... :? The trouble with fitting Sozo's here is you will need to redrill the circuit board in order to fit them in. If you do go down this route, use a small hand drill, and drill from UNDERNEATH the board, from the copper side through to the top. Failure to do that WILL cause the copper traces to lift off the board.

You should be able to fit a Sozo .68 in place of that .47, as originally that would have had a mustard in that slot.
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Re: NAD: 1976 Marshall JMP 2203 with Superlead cosmetics

Post by JPB » Sat Feb 23, 2013 4:47 pm

I think I may have muddied the waters posting two different amps. That V1b .47 Lego cathode cap is in the JCM 800 and the green .022 cap is in the JMP as shown below in the brown wire's path. As you can see on this JMP, there actually is a .68 mustard there.
Image
So, If I'm understanding what you're saying correctly, it sounds like I should expect to have a hard time finding a drop in replacement for that small green .022 coupler?
But as far as the cathode on the JCM800 the .68 Sozo mustard should drop in, in place of that .47 lego just fine as far as lead spacing?
My apologies for any confusion. :oops:

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Re: NAD: 1976 Marshall JMP 2203 with Superlead cosmetics

Post by demonufo » Sun Feb 24, 2013 5:42 am

Ahh yeah, getting confused there. :oops: :lol: The correct replacement for the .68 on the later amp may well be a MKT 1822 but you'd have to check the lead spacing with the original holes to make sure. Colour will vary from the originals though. http://uk.rs-online.com/web/p/polyester ... s/1666061/" onclick="window.open(this.href);return false;
The Sozo won't fit on that board either.

And yeah, finding those green .022's or even the later white ones will prove near impossible. You may have luck in sourcing NOS ITT or RS branded caps used in that era (76-77) though. A creamy brown coloured PCB mount cap.
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Re: NAD: 1976 Marshall JMP 2203 with Superlead cosmetics

Post by Loopytoots » Mon Apr 16, 2018 8:17 am

Changing the feedback from the 4Ω tap to the 8Ω tap feeds back a larger voltage so it increases the negative feedback, not reduces it. That’s why the amp is smoother and more controlled. Also, the yellow brick cathode bypass cap being 470nF instead of 680nF reduces the bass a touch more, but probably won’t be noticeable. Only raising the cap value would increase the low end and flub.

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