Evolution of the 100 watt superlead circuit

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Evolution of the 100 watt superlead circuit

Post by VelvetGeorge » Wed Jan 26, 2005 5:15 pm

A work in progress.

In order to trace the evolution of the superlead circuit, and to help us communicate about the different eras. I'll try to chronical it here.
I'll update the info as I have it.


'65 the JTM45/100

100 watt version of the JTM 45. Also called "Super Amp". 1202-84 Drake OT (8,16, 100V taps) 4k primary. KT66's. Radio Spares or 1204-43 (3" stack) PT.
Standard JTM 45 circuit. Shared Cathode. 270k mix resistors.
27k NF. .1uf PI caps. 56K/250pf in tone stack.
Non-voltage doubler PT. Bright cap varies by model, but 100pf seems most common.


Late '66 to early '67 Transistion to EL34's, steel chassis and gold rear panel. Earliest JMP's.

Still 2" Drake OT, the 1202-119 (8,16 and 100V taps) or 1202-132 (4,8,16). Both with 1.7k primary. Sometime in '66 the Drake 1203-80 voltage doubler PT came in to use. More research needed on PT's.
Filtering now is 100,100, 32,32, 32 (mounted on chassis), 16,16 (on board).
470k mix resistors. 56k/250pf tone stack. .1uf PI caps.

Mid to late '67 Change to Dagnall 1.5" OT's.

Most other specs the same for a transitional time peroid leading up to the 12000 series.

Very late '67 to early '68. The 12000 series plexis. Named for the serial #'s in the 12xxx range. EVH's famous amp is from this era.

Now we see the first split cathodes using a 820/.68uf combination. Normally with a 820/.68uf in V2 as well. The Tone stack changes to the 33k/500pf arrangement. 47k NF. .022uf PI caps. .0022uf cap in the bright channel V1.

Late '68 to July '69

All filter caps now mounted on top of chassis. The .68uf cap in V2 shows up intermitantly. And the 2.7k replaces the 820 in the split cathode on V1.
47k NF resistor.
Filtering is now all dual 50uf cans.

July '69 The metal panel era begins.
Last edited by VelvetGeorge on Sun Apr 17, 2005 3:07 pm, edited 4 times in total.
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Post by VelvetGeorge » Wed Jan 26, 2005 6:13 pm

Like I said, it's a work in progress. And nothing with Marshall is ever written in stone.

If you have any info to add, or see any mistakes please add them to the thread. I'll edit the post.

George
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Post by VelvetGeorge » Thu Jan 27, 2005 3:17 pm

Ya know, I've seen a few examples of shared cathode with the .68uf added in V2. And they looked stock, but maybe the .68 was added.

Can anyone confirm or deny this?

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Post by Flames1950 » Thu Jan 27, 2005 7:27 pm

We thought you were the guy to do that for US...... :wink:
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Post by Guest » Mon Jan 31, 2005 9:49 pm

Boy, you opened a "can of worms" with this post George. I think that when someone traces the transformation of the Super Lead circuit you have to ask yourself; when or at what point do the "little" subtle differences become insignificant. I have looked at hundreds of Marshall amps built between 1964 through 1969 and there are tons of "little" differences between production runs.
The 100K feedback resistor is a 1972 (or extremely late in 1971) feature and should not be OEM on a "plexi" amp.
Secondly, the 0.68uF bypass cap found on a "plexi" amp with a shared cathode arrangement is not a stock setup. I believe you might find that in the "Lead Bass" amps made for a very short time in the 70's.

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Post by VelvetGeorge » Mon Jan 31, 2005 10:23 pm

Thanks for the info, I'll edit the post.

This is a can of worms indeed. Every time I think I have a revision pinned down, I find evidence against it.

Marshall seems so inconsistant during that time period that I should put a disclaimer at the top of the post.

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Post by Guest » Tue Feb 01, 2005 9:28 am

After reviewing my post I think I was addressing the "component" changes moreso than actual circuit changes. There are indeed multiple circuit changes, but component changes outweigh it ten to one. Marshall inconsistant!.....That's an understatement!

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Post by Mr G » Tue Feb 01, 2005 10:30 am

Hi There,

First things first, great board and great products - I have been an admirer of this website for a while now, and its nice to see people taking a genuine and positive interest in this hobby - for all the right reasons. Long live the eager amp hobbyist/builder!

I just wanted to give you my 2 cents on some of marshall's production timelines (obtained from a friend in the UK working with Marshall on their new HW series amps) - regarding some of the afformentioned dates in your post. According to the man in charge of fabrication at Marshall during the late 60's (a Mr Ken Bran), they never made any steel chassis amps in 1967 - only alluminium. So forget about the move in 67 to dagnall 1.5" tranny's....this may clear up a lot of misunderstanding as to when the ~switch~ from Drake to Dagnell actually took place

Feb 1968 was the very first time steel chassis amps were made (due to the move to the new factory in that month - along with the purchasing of better presses for bending mild steel). Many components, boards, transformers etc....were made in late 67 in anticipation of the move to the new factory, but there really is no such things as a 1967 assembled/made Super Lead Plexi. They were all ali chassi amps.

Many of the parts were made before feb 68, but NOT ONE STEEL chassis was made in 1967.....which kinda shakes up the whole transformer code, component changes theories...the english were never great at traceability or accurate date part marking...(in those dayz;-)

The repercussion of this information could spread far....(hopefully in a positive sense). I am sorry for those who liked to add an extra $1000 to the value of their prized Hendrix/EVH 67 SLP...just because they THINK its a 67......Well......sadly, I can tell you that every steel chassis amp ever made was made from 1968 onwards....they had quite a few variations as i'm sure you are all aware of - and some that made no sense at all (in terms of parts/arrangemment used)

To confirm my statement(s), please feel free to contact Phil Wells, Laurent, Danny or Mitch Colby at Marshall to respond to what i have mentioned [through a friend of mine in the UK] - in light of recent conversations they all had with Mr Bran himself - who has quietly retired in kent somewhere (south east england)

I hope this didnt stuff the timeline approach too much George??? - apologies if it did....I am only trying to perpetuate some better certainty in people's understanding of when these things were made.

Cheers for now

Mr G

p.s. the whole ~falling out~ incident rumoured to be between Ken and Jim was hype/nonsense....its just that one tiring day Ken realised that he was doing 16 hour days 6 days a week and missing out on bringing up his second child after many years slaving at Marshall.....I dont blame him really...I'd do the same!

GOD SAVE THE QUEEN!

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Post by Guest » Tue Feb 01, 2005 8:58 pm

Extremely interesting info "Mr. G". The first question that pops in my head is; How could Marshall put out a 1967 catalog (presumably in may '67) which clearly shows amps with the reverse type logos which were all made on steel chassis?

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Post by Mr G » Wed Feb 02, 2005 6:03 am

No idea "Mr Guest"....what 'reverse logos' are you talking about.....please explain as i am not aware of any reverse made logos?....I could be misunderstanding you though...do you have any detailed pictures for illustration?

I regards to your statement about the catalogue timings....i havent got a clue to be honest.....can anyone reliably tell you when these were made? or when the images were added/released? I guess one could go a bit mad trying to find it out.....

The only info i can go on came originally from Ken Bran himself through marshall through my friend. I know age can do things to your minds recollection of events, but Mr Bran still seemed to have all his marbles....and was very cogniscent and clear in his thoughts.

I hear that there is a lot a sun spot activity at the moment....hmm

p.s. Well done Man U - 4-2 against Arsenal....

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Post by Flames1950 » Wed Feb 02, 2005 8:21 am

Is "reverse logo" referring to the "black flag" JTM's?
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Post by Guest » Wed Feb 02, 2005 12:46 pm

Sorry about the somewhat unclear post. Yeah, the reverse type logos is what many refer to as the "black flag" JTM logo. Just to add fuel to the fire, I quickly looked for info regarding the factory relocations throughout there early years and I didn't come up with any moves during the late 1967 era. There was a move around June 1966 to the Lyon Road address which might be what Ken was reffering to. Other than that the only other relocation around that time was the move to the First Avenue address around October 1968. I'll see what else I can dig up.

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Post by Guest » Wed Feb 02, 2005 10:13 pm

After some further investigating I noticed that the catalog stated as 1967 (in the Doyle book) seems to mesh exactly to the July 1968 price sheet page for page, amp for amp. No where in the catalog does it state the year, as do any of the early catalogs, so this opens the door to possibilities. There is a "disclaimer" in the forward stating some degree of inaccuracy. I did notice that there is another 1967 catalog (from early 1967) that was not printed in the book. So, this leads me to believe that the one shown is suppose to be a "late" 1967 catalog at best. Nonetheless, amps such as the "Power Builder" were supposedly built in mid 1967 and they are on what looks like a steel chassis judging by the use of cage nuts. In addition, there's the whole Marshall "Major" or "pig"; called at the time; issue too. If memory serves me correctly, the very first "pig" amps had the aluminum chassis, but quickly was changed to steel because of the shear weight of the transformers. These amps definately were produced in 1967.


Lets just say that Marshall didn't produce any steel chassis in 1967. For some reason the production figures just don't seem to add up then. 99% of the amps built on aluminum chassis carried the "Ser." prefix for the serial numbers. Amps built on steel chassis use the more familiar "SL", "SB", "S", etc.... adding up the numbers of these later prefixed amps and keeping in mind the mid 1969 deadline just doesn't jive with me. I'm reffering to the number of amps when I said "numbers". Were talking thousands of amps produced in 14 or 15 months here. Just doesn't seem right compared to the production data a half year earlier. Kinda get what I'm driving at here? I know Marshall was enjoying explosive growth at the time but this seems too excessive to me. Anyway, food for thought.

Guest

Post by Guest » Thu Feb 03, 2005 11:35 am

Nice work Guest...you are lucky to have the free time to investigate these things. Funny how when you look at this kinda stuff you realise how unorganised/accurate much of the data was during the time eh?

I have attached a picture of what i think is a reverse logo / black flag amp. It sounds incredible to say the least. Can you confrim with me this is what you were refering to?

This amp was made in early 68....from what i can tell. However, I have found something which i believe could be a ~reasonable~ indicator (in the last few years that i have seen, played and tinkered with these things) of the year of these sacred amps....

I have never seen a 67 (or before) marshall amp with the later series brighter yellow resistors....cant remember who made them....a czech/yugoslav company (Iskra maybe???) Whereas, On every ali chassi amp i have owned/played/seen, they were all the much darker red/brown types....ALl the amps i have seen that had these later series resistors seemed to always be steel chassis, starting approximately in 1968....

Interestingly, ecery steel chassis amp i have seen always had these nwer style brighter yellowy resistors.....i hope you know what i am talkign about here?
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Post by Guest » Thu Feb 03, 2005 9:37 pm

Nice amp....And yes that is what I was reffering to when I mentioned reverse type (typeset) logo. I may have to refer to my self as "guest#2" if I never register in.. Anyway, steel chassis I see. Interesting to see a Dubilier of England filter cap on the board since Marshall never really recieved too many of them from R.S. I know which resistors your talking about (yellowish colored) and it's true you don't see very many installed on aluminum chassis amps, but there are some amps that have a few. Mostly the aluminum chassis amps used the dark red colored carbon film resistor everywhere except for like the feedback, 820ohm cathode positions along with the 100K cathode resistor for V2b, and of coarse the H.T. dropping resistors which were usually carbon film types. Anyhow, may I ask how you determined that your amp was probably made in early 1968? Do the "mustard" caps bare "D7W" or "A8W" codes? Let me guess your thinking maybe April 5th 1968, right? I do have a request that I hope you can indulge me on; Can you please tell me what the voltage rating in on the yellow colored "cube" looking (WIMA I believe) capacitor that's connected on the PRESENCE control? And while I'm in "question mode" here; what's the serial number of the amp?

I did a little more thinking earlier about the steel chassis issue and the creation of the 100w amp came to mind. If the 100 watt amp was "born" in late 1965 (Fall) and went into production in early 1966; then I can see a problem arising. The first 100w amps used the JTM45 faceplates, right....That would mean that Marshall used the JTM45 faceplate for approx. 2yrs and a couple of months if steel chassis didn't start until Feb. 1968. In turn, that also means that Marshall used the creme colored back panels for an equal time. Maybe it's me but it just doesn't add up. :roll:

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