Storage Diving: '72 JMP50 Resto Time

stratburst

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I've been going through my storage unit recently and discovered several amps I picked up years ago on a hoarding binge that I kind of, well forgot about. When I picked them up I intended to get them serviced but I didn't live near anyone that I trusted to go through them at the time, so they went into storage. Now that I'm in Nashville and have a tech nearby I can trust, I've been pulling them out one by one to go through them. Up for consideration today is a 1972 JMP50 lead with original OT and laydown PT. It's headed to my tech soon and I'm looking for input on what I should be asking for to restore it.

First up are the PI coupling caps, they have to go. Would this amp originally had the same Philips "chicklet" caps used elsewhere in the amp as bypass caps? I have not been able to source these caps anywhere but I do have some .022uF/400v mustard caps I could use if it makes a sonic difference.

I also note that one of the sockets have been replaced. Probably a little difficult to source a correct replacement. I can ignore that as it functionally is sound.

Although I use NOS tubes I do plan on adding some Welwyn screen resistors.

Any other changes stand out that I should address?

Cheers!

20210923-155019-2.jpg
 

Ivan H

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First up are the PI coupling caps, they have to go. Would this amp originally had the same Philips "chicklet" caps used elsewhere in the amp as bypass caps? I have not been able to source these caps anywhere but I do have some .022uF/400v mustard caps I could use if it makes a sonic difference.

You shouldn't have too much of a hard time sourcing those yellow Philips capacitors. I've not too long ago bought them in complete sets (for 70's marshall amp builds) & also as singles. They are more readily available & much less costly than mustards. If you want I can look back to where I sourced them & pm you the supplier's details. Cheers
Edit;
@playloud beat me to it (I got side tracked mid post). Wazzgroover is the seller I got them from. Cheers
 
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stratburst

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I tend to prefer shared cathode circuits and have heard these caps can be bright in a lead circuit. I do recall the amp was very bright when I bought it, one of the reasons it went into storage. Will swapping out the orange drops for mustards tame the high end a bit?
 

neikeel

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If you struggle I have the caps and correct socket.
 

mAx___

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I tend to prefer shared cathode circuits and have heard these caps can be bright in a lead circuit. I do recall the amp was very bright when I bought it, one of the reasons it went into storage. Will swapping out the orange drops for mustards tame the high end a bit?
I doubt it will have any dramatic impact unless you use a different value than stock. I'd just lift one leg of the bright cap in Vol 1.
 

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