• Guys, we've spent considerable money converting the Les Paul Forum to this new XenForo platform, and we have ongoing monthly operating expenses. THE "DONATIONS" TAB IS NOW WORKING, AND WE WOULD APPRECIATE ANY DONATIONS YOU CAN MAKE TO KEEP THE LES PAUL FORUM GOING! Thank you!

71' Marshall Metal Panel finished / Pic's

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
Had to repair the bias pot. Rewire the bias to the hot side of the standby. Removed the wire from the 220k to the rectifier and installed from the 220K bias to the Hot side of the standby. Install a NOS .68 Mustard on V2 cathode. Installed screen & bias resistor's on the power sockets. Blew / shorted one of the .22's off the PT secondary to the filter cans. The big silver cans on the board. Some amps have them removed or not in the circuit. Cannot find .22 electrolytic's but Metro had all the parts and I used Xicon .22uF / 630Vdc caps......Nice, dollar apiece and way better than a electrolytic can. Also bought F&T filter caps but left them out till needed. The Daly's check and sound fine so far. Amp very quiet. Turn on with both volumes up and no noise or static, popping etc. That way I have them and do not have to wait to play this thang!!!! I bought it all original and the bias pot went....ordered and fixed that. Played it for half an hour and when shutting down it just fizzeled out....quit working:bug Found the Shorted .22 Can. Removed and fired up and did a voltage check and all was well:lol Ordered again the parts....just fixed and rebiased the Mullard Xf2's. Took Pic's..........:applaude The 71' is on top and the 72' on the bottom. Marshall cab has 2x12 Celestion Heritage 20 watters and 07' R9 from Vic

P1010018a.jpg


P1010004a.jpg


P1010003a.jpg


P1010011a.jpg


P1010013a.jpg


P1010021a.jpg


P1010027a.jpg
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
It is all original from 11/71' Must be when they started the large head cabs. I bought it from a reputable dealer in the UK. Everything in it was stock. That's why I had to change a few things. Everything looks the same, The box and chassis has all the same wear and oxidation. I'am no expert but they used what ever they had on hand to put out production......The tag and everything is all there. The amp is in Excellent condition inside and out. must been in someone's room for years. Still had the original Brimer's in it. One shorted in shipping, so I put in a set of Xf2 Mullards. And I tested the 12ax7's and all tested at minimum or below, so I installed Mullards and a Telefunken smooth plate. Tested on my newly calibrated TV-7. My 72 is from 3/72'. When was the large head box issued for 50's??????
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
A '71 50 watt in a large head cabinet?

I just got thru discussing this with the dealer and he says that's when they started to come out. Mine might be one of the first, all original. His shop has been in business for decades. His tech has been doing tubes for 45yrs! Which can be a good or bad thing:hmm They biased the amp using a scope.....way to cold for me! That's old school. You can bias a amp three different times with a scope and probably get 3 different readings. I discussed this with Greg Germino the other day and we are in the camp that el 34's do not need this 70% bias. El 34's get alot more signal therefore needing less current. 60 to 65% should be fine. My 71 has 442 Vdc on the plates with 30mA and 35mA on the Mullard Xf2's. There 5mA apart. Which I like now, more overtones and harmonic's. I use to have perfectly matched tubes and PI. The beauty of old amps is the out of spec. Sometime's you get the one that is the Screamer and Tone! Now I use a very high Gm tube in the Phase Inverter. I want the tubes to be driven at there best. It does not have to be perfect anymore, matched triode. Having my own Calibrated Tv-7 also helps. Especially buying NOS. That way I know if I am getting what I'am supposed to be getting.......:hmm 6L6GC's I bias warm around 70%.
 

Emerald

New member
Joined
Dec 5, 2007
Messages
1,123
Yes the MK II JMP 50 watt metal panels were in big boxes, just ask Yngwie..:lol :lol , '71 may well be the first year or so..
yngwie308
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
Well I had a chance tonight to let her warm up and put her thru the paces. When I first retube and bias an amp when I get to playing past half throttle I look at the power tubes to make sure there is no red plating. I leave the back off of the heads...cooler. Well one of the Mullard's started to red plate. Well back to the bench. I installed a NOS different set of Mullard Xf2's w/double getter's at 60% bias at 442 on the plates. Mullard's in V1, V2 & RCA very high Gm on both triodes in V3. 07' R9 "Y" corded direct shot..........this thang roars at 6 & 6 on both volumes thru the 2 celestion Heritage 20 watters. Very nice speakers and I do not worry about blowing them. The 20 watters add alittle damping on the db rating and sound great. Very glassy sounding on 2 & 3 playing chord's. Also has good note definition. This one has the laydown tranny and is a Keeper. My 72' has the upright at 363Vdc on the plates. Very sweet amp. for those who want the Marshall tone without Killing try one with the upright or later laydown with the low voltage....very great and sweet sounding metal panel's:salude
 

jcs

New member
Joined
Oct 31, 2001
Messages
2,106
Did you install a new bias pot?

If so, where did you source one (from Metro)?

I need to do a few things top my 71 smallbox 50 like change the bias pot.
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
I got all my parts from Metro. The 25K bias pot fits perfect. You should be able to see it in the Pic's. Black Verticle pot fits right in....just barely had to move the ends with a pair of needle nose to fit inside the solder holes. Call them up and tell them what you need. Great Service and Price's. Fast Shipping. Call early the mail goes out early there. Priority mail.
 

markguitar

Les Paul Forum Member
Joined
Nov 27, 2001
Messages
2,363
Of course 50 watters came in big boxes, I just thought '72 was the first year. My '71 JMP50 is a small box and it's dated Aug 14, 71.
Here are some pics of her:

http://members.cox.net/dgrover/1971_marshall.htm

Dave, You are correct!! A '71 should still be in a small box without a doubt. I've even had '72's in small boxes. I would guess that this chassis is not in it's original box. But it's impossible to tell. You can only go with what seems to be the norm which would be for a '71 with a laydown mains transformer to be in a samll box.
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
Dave, You are correct!! A '71 should still be in a small box without a doubt. I've even had '72's in small boxes. I would guess that this chassis is not in it's original box. But it's impossible to tell. You can only go with what seems to be the norm which would be for a '71 with a laydown mains transformer to be in a samll box.

Well the amp came from a reputable dealer in the UK. The chassis and box look all original with the same wear. the date is 11/71. Can you say for sure that I was lied to???? That there is no way a 71 marshall 50 watt in Nov of 71 came in a large box??? The chassis and box look too original to be a different box. My 72 from March is in a large box. The dealer said it is probably one of the first to come out. That they started to come out in late 71' I would like to know:hmm I've also seen laydown tranny's in later 70's models, later than 72. Is there a place a can run the serial number and find out???? I just looked in the History of Marshall and it says "around" 72' they standardized to the large box with no vents. Well 11/71 is around 72. And I would believe that if they had one to sell and no small box a large would do. I also emailed Marshall with the serial # but that could take............S/A 50XXC. I will call a few Vintage dealers to get input.
 
Last edited:

markguitar

Les Paul Forum Member
Joined
Nov 27, 2001
Messages
2,363
Well the amp came from a reputable dealer in the UK. The chassis and box look all original with the same wear. the date is 11/71. Can you say for sure that I was lied to???? That there is no way a 71 marshall 50 watt in Nov of 71 came in a large box??? The chassis and box look too original to be a different box. My 72 from March is in a large box. The dealer said it is probably one of the first to come out. That they started to come out in late 71' I would like to know:hmm I've also seen laydown tranny's in later 70's models, later than 72. Is there a place a can run the serial number and find out???? I just looked in the History of Marshall and it says "around" 72' they standardized to the large box with no vents. Well 11/71 is around 72. And I would believe that if they had one to sell and no small box a large would do. I also emailed Marshall with the serial # but that could take............S/A 50XXC. I will call a few Vintage dealers to get input.

Like I said, it's impossible to know for sure and there's no way to prove it either way. So it's probably not worth all of the extra work and research. There are no sure rules or positive dateline you can follow with Marshall. Only what people who have had a lot of Marshall stuff would consider the norm. If you got the head for a decent price and like it, doesn't much matter. I'm sure there were still some small box heads that were shipped even after the box box 50's started. Certainly wouldn't be uncommon to find unused small box cabs hanging around the wood shop after the change over.
 

BIG Dave

Active member
Joined
Aug 18, 2001
Messages
2,420
And I would believe that if they had one to sell and no small box a large would do.

That's always seems to be the case with Marshall. Do whatever is needed to get the amp out the door. I assume it's possible that Marshall started thinking about standardizing the box size around that time and put a few out in late '71. Then perhaps there was a transitional period where 50 watters were coming in both small and large boxes up until early '72. Best to ask Ken Underwood (profile name: G3SDW) at the Plexi Palace BB. He was with Marshall from the start and worked alongside Ken Bran and Dudley Craven. If anyone would remember, he would!
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
I emailed Marshall and will call a few vintage dealers. The UK dealer has said that this is original and does not sound like someone to say things that are not so. He has alot a Bitchen!!! english gear so why would he say something that is not true....Bad for Business. I own a 64' Blackface Princeton. It has 4 white knobs, Brownface circuit and blackface power supply. Does this mean that it is not original........NO! It is one of the first Blackface Princeton's made. What is called a "Transitional" model. I could tell by looking at it, buying from a reputable person and work on and build my own amps. I opened it up and looked at all the solder joints and schematics to figure it out. GZ-34 rectifiier! for a Brownface! This little bugger Screams...Also had an Oxford 10K5 in it instead of the later 10J5. Does this mean that it is not original????? In transistion periods with Marshall and Fender they put in what ever they had at the time!! And even not in transition periods they put in what ever they had. This amp looks to original, chassis and cab have the same exact wear and oxidation. If it was changed it was a very long time ago. This amp has the tone to die for....gotta love the debate!
 

ptrickamp222

New member
Joined
Aug 22, 2007
Messages
879
Well I just emailed some very Marshall folks and had a number of reply's that the large box came out in 71' As early as Aug or Sept!!! So I will take it that it is original.......I have more than a half a dozen saying that they came out in 71' and one person saying that it isn't so........It looks original, wear, oxidation, etc. It's hard to believe that on Dec. 31, 1971 they stopped using the small box and on Jan. 1, 1972 they started to use the large box for 50's. Jim Marshall and Leo Fender used what ever they had at the time to get it out.That's my story and I'am sticking to it.............:salude By the way the one person that said it is not so I still check out your site all the time! Thanks to all for your input:applaude
 
Top