1971 Marshall 100Watt Super Lead 1959 cap job

[TubeNV]

I just acquired this 71 Super Lead el34 powered head off Ebay & it will arrive with what was diagnosed by a tech in Cali as faulty filter caps.
What would be the best performing caps for this job & the best place to get them?
Secondly, where can I find a reliable schematic for this year head? I've copied the one off Dr-Tubes site marked as MARSHALL 1959 MARK II dated July 1970 & also marked Unicord 70-6-11 which I think dates it as June 11,1970 but, I seem to find this same schematic everywhere I search & would like to know if this is the definative, accurate & only schematic needed for any & all work, now & future, one may need to work on a 1959 model manufactued in 1971.
These 'Metal Panel' Super Leads did morph over the their production years with power tube changes and variations available & a second pair of 1/4 speaker output jacks being added but I am not aware of any big changes from 70 to 71 with the el34 variation.
This is my first post so be gentle to the newbie you knowledged brutes. Hopeing this is a useful post as the metal panels are more affordable than the plexis yet offer relative similarity in tone & response since Marshall went solid state rectifier in the 60s making them the affordable to own plexi tone so, similar situations are sure to happen. Besides, who doesnt love to talk about vintage Marshalls. Rock on & thanks in advance for all the knowledge & info.

[jmaf]

I just acquired this 71 Super Lead el34 powered head off Ebay & it will arrive with what was diagnosed by a tech in Cali as faulty filter caps.
What would be the best performing caps for this job & the best place to get them?
Secondly, where can I find a reliable schematic for this year head? I've copied the one off Dr-Tubes site marked as MARSHALL 1959 MARK II dated July 1970 & also marked Unicord 70-6-11 which I think dates it as June 11,1970 but, I seem to find this same schematic everywhere I search & would like to know if this is the definative, accurate & only schematic needed for any & all work, now & future, one may need to work on a 1959 model manufactued in 1971.
These 'Metal Panel' Super Leads did morph over the their production years with power tube changes and variations available & a second pair of 1/4 speaker output jacks being added but I am not aware of any big changes from 70 to 71 with the el34 variation.
This is my first post so be gentle to the newbie you knowledged brutes. Hopeing this is a useful post as the metal panels are more affordable than the plexis yet offer relative similarity in tone & response since Marshall went solid state rectifier in the 60s making them the affordable to own plexi tone so, similar situations are sure to happen. Besides, who doesnt love to talk about vintage Marshalls. Rock on & thanks in advance for all the knowledge & info.

Hi TubeNV, welcome to the forum. I'm not what you'd call a knowledge brute(first time I ever heard that), but I do my best to help.

First of all, congrats for your buy, but do wait for the head to arrive so you can post us some more specific info. What did the faulty caps do? Fry the entire power supply? Or are they just leaky and running warm? There's a whole range of "bad" stuff that bad caps can do, sometimes bad caps just let hum through, in which case they're telling you they'll go kaputs soon, or they have already failed, in which case you should assess the damage.

Off top of head, if customer walked in with one of those in hand, first I'd think damn cool, I'm having fun today. Second thing I'd think is "cap job". Third, potentiometer test, change if needed. Fourth: tubes. Fifth: ROCK!

So hang around while it doesn't arrive, and hopefully you can post some pics and more detailed info on the exact cap failure you had

[TubeNV]

Thanks for the welcome & advice Jmaf. Fortunately, the amp is reported as working & has the cap hum symtom. This was a 'selling for a friend' deal with a $100 shipping quote & a mention of cap work needed in the $200 range. This obviously scared most away from bidding but I did read carefully & found that the shipping was just a rough number & actual shipping cost would be charged & that $200 would be taken off the final amount for the cap job. As long as the amp arrives as described I will be very happy. It looks really good for a 71. After calling the owner & asking some questions, I felt comfortable enough with the arrangement & price to see the deal through. He said it was sitting for some time & he powered it up without being able raise the current a little at a time. Time will tell if I did ok or not.
I have attempted to add a pic of the chassis underside below. 1st attempt at it so hopefully it works. The link will only be active for a short time as its ebays cgi bin. Maybe it is all 5 pics, not sure. Let me know if it works will ya? If not we have to wait till she gets here.

Thanks for your interest. Cant wait until she's %100 and hit that first A power cord. I wonder if Wont get Fooled Again or Highway to Hell will follow? Maybe some Zep or maybe I'll have to put down the Paul & change the undies?

[Gtr_tech]

I like the F&T cans for those.
F&T - Germany Radial Can Capacitor 50µFx50µF / 500V

[Gtr_tech]

Also, be sure to replace the other electrolytic caps whilre yer "in there". The bias supply and preamp cathode bypass caps are all old and tired if they're original.

[TubeNV]

Gtr_tech, Thanks for the info & link. That looks perfect & the price is reasonable. Also being you prefer to use them, I will dare to assume performance & tonality are there also. I may wait to change any other caps so long as they are working without issue to preserve as much original appearance & tone as possible. This is also to maintain resale value as most will choose to buy a head like this because it doesnt look messed with. Thats a big reason why I like the filter caps you turned me onto, they look great as well as do the job well. Be assured anything that doesnt spec will be relpaced. Now where could I find vintage looking mustard caps for the other stuff if needed without going the unreliable NOS route? If you had the choice, would you grab the amp that looks untouched & working or, one with orange drops put in by unknown? Interesting eh?
Also, the second part was about finding a reliable period correct schematic. Any leads on that? Thanks again. It is much appreciated. Barry

[riz]

I'd rather find an all original amp. I enjoy going in and working on something has hasn't really been touched. It's like an archeaological dig! Not going to get too into preaching about caps... but to say that I always change the electrolytics in mine, and any other component as needed. If it's too precious to maintain, it's too precious to play. At least under my roof.

[Gtr_tech]

Don't worry about the "mustard" caps. Those are coupling caps and they *should* be OK unless you have problems related to a cap leaking DC in the signal path. I was referring to the 10u caps in the bias supply. These are important parts in the output section and if one is leaky it can cause bias drift. If one is shorted or super leaky, the output tubes will redplate in a hurry.

The electrolytics in the front end you can leave if you want, but 40 year old lytics don't work well these days. Tone will suffer with tired caps. I'd replace them.

Its a bit like buying a 1971 Camaro that is all original, including hoses and tires. It will look nice, but won't be usable due to the rotten hoses and tires that won't hold air. This is not an amp I'd cut corners on. Do it right the first time....

[riz]

This is not an amp I'd cut corners on.

Couldn't agree more.

[TubeNV]

That's a cool way of looking at the situation. Now should I simply update the bias caps or leave em if they are currently working well. Or are they like that old hose that is working fine one minute & spewing coolant after flooring for too long? If replaceing them, what brand should I use? &, is there any noticeable effect or variation on tone when using different brand caps in the bias section?

[jmaf]

That's a cool way of looking at the situation. Now should I simply update the bias caps or leave em if they are currently working well. Or are they like that old hose that is working fine one minute & spewing coolant after flooring for too long? If replaceing them, what brand should I use? &, is there any noticeable effect or variation on tone when using different brand caps in the bias section?

Caps may show some signs they're about to fail, but normally you don't see them before they do, but you may hear some hum. The bias is too vital a circuit, I'd replace the caps with as close to originals as possible.....

[riz]

Replace them/it. Do what Marshall did: use the cheapest caps of correct rated value you can find. That may seem like a smart-ass comment but it's not.

[TubeNV]

Copy that Brother. I will do the bias section to keep things stable. Here is where my aprehension about replaceing parts & useing the 'right' replacements come from. I wont mention names because I dislike name droppng braggers & would hate to seem like one myself. I did get to hang with a successful boutique builder who was adamant if not obsessive & anal about parts & layout. I mean this guy was able to not only demonstrate tonal difference in cap brands but also variation in tone thruogh wire length, type of wire, shielding & the path of wire as well as grounding things in different areas on a chassis. It impressed me as to how important every seemingly insignificant little thing goes toward the overall tone of the amp. That is why I was hesitant about replaceing original stuff that might currently be working well & why I search & ask for the 'right' replacement brands to use that offer the appropiate tonal response. With such an iconic tone monster, I just want to nail it right the first time I solder something in as well as leave it looking as close to original as possible. It might be that the bias caps have very little affect on tone & haveing the proper & stable current in this section has the greater overall affect on keeping the amp as it was meant to sound. Do you personally find this to be true in the bias section or will any cap with the correct values offer the same tonality? The lessons learned with this guy opened my eyes but also left me questioning everything I do to an amp. A blessing & a curse that haunts my every move. Do you hear creepy laughter??

[riz]

Right on, I had a studio guy once show me all the different wire he used as patch cords, because they all sounded different to him. I have experienced it myself using jumpers while working on projects. It sounds like you have a pretty well thought-out, and somewhat educated, aesthetic toward what you are trying to accomplish, and I applaud that. Nothing like a job well-done on your own amp, that also pleases your eye. For instance, I really like Sprague Atoms as power filters and black-and-green Mallorys as bypass caps in my Fenders--because I like the way they look--but I doubt I will be buying more once my stock is used up because of cost and questionable performance (I've read, with the new ones) these days. Elaborating on my previous comment, any new cap from a reputable source, that you also find aesthetically pleasing in addition to possessing the correct values for the circuit, will be an improvement over what was in there originally. I myself have not worked on many old Marshalls, but I own one, and I have read that the bias circuit can be someone finicky or unstable, and perhaps this has lead to the myth that the original output transformers were temperamental. Well, that, and the fact that everyone ran them on "10".

[riz]

Maybe I just hang out on the internet too much, but the F&Ts do seem to be a happenin' thang in Marshallandia these days. Haven't tried 'em myself yet. One of these days my '74 Super Lead WILL be coming apart again for some major overhauls. It is currently resigned to a dark corner of my studio because of an ongoing intermittent problem. Google "ESR", in regards to capacitors...