Marshall JMP 50W '67 and '71 - How original? (Pics + sound clips)

[soundboy57]

Can't decide which I like better, but I lean towards the 71...beautiful amps you have, what great tone. And like your licks, too!!
Great videos.

 

[Jucciz]

As for the date of manufacture I'd say very late '67 or early '68. I'm leaning towards very early '68 since the PT has a dedicated 120vac voltage tap, and the Dagnall C1999 choke. You could also check the potentiometers for a date code which might also help narrow down the date of mfg.
It does look like someone might have removed a bypass capacitor from the mixer resistor assembly. Personally, I'd go with a 500pF or 560pF bypass cap for the mixer resistors rather than a 5000pF volume pot cap. I think if your patient enough and constantly hunt of a Lemco or RS cap you'll find one, but in the mean time you should just pickup a silver mica 500pF or 560pF cap to use.
I think the Welwyn W22 1K/5W resistors would be a good choice. For the 100w amps of this era Marshall used Welwyn, the gray RS branded resistors, and the cement DCC resistors.

Thanks for this very informative post!

I might try a silver mica in the meantime. The amp was sold to me as a '67, but I understand it's a fine line. It's of course the tone that matters!

And an early '68 plexi ain't that bad after all...

 

[Jucciz]

Can't decide which I like better, but I lean towards the 71...beautiful amps you have, what great tone. And like your licks, too!!
Great videos.

Thanks!

As stated earlier, it's my friend Sam Vilo playing in the videos. The tone is all there: in the hands, but also in the amps. The Les Paul shown in the videos is mine too: a '59 Reissue (R9) from '96 (the good tonewood and not-your-average flame maple top years).

Btw. Sam has a huge collection of guitar gear videos in YouTube. Check them out!

 

[FutureProf88]

I'm sorry I don't have something more productive to add but wow that '67 sounds beautiful. I love the sound of the pre-superlead amps.

 

[metromutt]

Btw. Sam has a huge collection of guitar gear videos in YouTube. Check them out!

I've had a few of his vids booked marked for sometime, Sam irritates me he's too feckin good at getting great tones recorded, there's never a bad sounding amp which goes to illustrate something about looking at youtube links to buy an amp best look for the worst then buy the amp ...things can only get better!!!

 

[Appetite4distortion]

Hi, I concur on the other people verdits: hard to say which one's best, both perfect examples on how a nice plexi tone should be. Rock/hard rock vs bluesy/classic rock and I have to choose with? I'll take both, thanks!
I agree also on the very early 68 date based on the dagnall choke, and also I would add cause of perforated board.
FYI I have a late 67 50 watter which is basically 99% identical layout, with few cosmetic and components differences, if wanna compare:

https://plus.google.com/photos/104449590667330584537/albums/5921393622531957713?banner=pwa

BTW sound is totally similar as yours, vocal on the midrange with that "hollow" fluted attack, bit less juicy/aggressive than the 71.

If wanna restore further, you can find on ebay sometimes original RS/Lemco 560pf which yes, was originally installed on the mixer channels and then removed.
The channel 1 would sound a bit brighter then. You can try it, but honestly the sound is almost perfect as-is now

 

[Jucciz]

One step closer to original: found a pair of mesh power tube retainers today, hooray!

The other V5 tube socket's frontmost screw has no slot for a screwdriver whatsoever - unlike the other three. I wonder why. Gotta find a suitable tool to unscrew the nut from inside the chassis. so I can loosen the screw and install the other end of the retainer. No big deal, I hope.

I found at least a couple amps in Amp Archives with similar retainers, so I think mine are legit. At least the seller claimed they were removed from a late 60's Marshall.

http://amparchives.com/album/Marshall/50%20Watt%20Series%201966-1981/1986%20or%201987%2050W/68%2050W%20SN%20S10782/slides/3755_p49593.html
http://amparchives.com/album/Marsha...7 50W/67 JMP 50W SN S11080/slides/eb91_3.html

Now someone find me an original gold-on-white script logo, please.

 

[damienbeale]

Did the 50w amps of this era generally have tube retainers???
It's not my area so you'll have to forgive my question...

I'm intrigued as to what those EL34's are. A very distinctive plate, albeit one I don't recognize.

 

[Jucciz]

Did the 50w amps of this era generally have tube retainers???
It's not my area so you'll have to forgive my question...

I'm intrigued as to what those EL34's are. A very distinctive plate, albeit one I don't recognize.

I linked a couple of other amps with similar retainers in my previous post. There must be more of them, but they surely are rare.

The EL34's are Telefunkens, probably from the 1960's. You can find pictures of similar tubes here - most of them seem to be 60's production:
https://www.tubeworld.com/el34telefunken.htm

Great tubes, I surely can recommend them!

 

[Jucciz]

To be more precise, the Telefunken EL34's are from 1967-1971 period (two round holes in plate with winged heatsink).https://www.tubeworld.com/el34telefunken.htm

 

[Jucciz]

Updated links to pictures below. The ones in the original post don't work anymore.

'67 JMP:
https://www.dropbox.com/sh/d913ianxq6dvvyp/AABW9Lvf99gBBADUFUDRQ52wa

'71 JMP:
https://www.dropbox.com/sh/8ubr8p45furwtjz/AACJJoBrjfJ2qYOR3s5rPGHKa

Just purchased a nice strong quad of Telefunken EL34's. That makes a nice pair for each of these amps. Also, the '67 received those nice mesh power tube retainers.

 

[Joshabr1]

Beautiful amps.

 

[usednabused]

Very nice amps Jucciz!