# When did Marshall Switch to PCBs?



## Olde Growler

I understand that Marshall switch from Point to Point to Printed Circuit Boards in 1973. What month in that year did they start producing PCB Marshalls?


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## Joshabr1

Somewhere around mid year. U have to understand that everything is not so cut and dry. Some models kept the turret board longer. But I think the general switch was mid year 73. I have a nov. 73 superlead that is pcb. Also the best amp I've ever heard in person. So if ur lookin for tone don't get caught up in the pcb////turret board debate. It's total bullshit.


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## Olde Growler

That is what I understand. I was looking to see if their was a specific month on the inspection tags that we start to see the transition for at least the Super Leads and Super Basses.

As far as tone, I am in agreement with Steve Vai, no Marshall is created equally. When you look under the hood of any of these early heads, you hardly ever see the same components from head to head whether it is a PTP or PCB units and one can surmise that they will sound different.

Now with that being said, the PTP heads seems to bring a premium over the PCB units. 

One other question, is there a correlation with PCB heads being labeled Mk II on the back panel?


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## AldermaticAmps

It's not really so cut and dry. Electronically speaking, there isn't much of a difference, but you do tend to get better quality components on PTP (or rather turret board) amps. This doesn't have to be the case, especially with what they can do with PCBs these days, but years ago, PCBs were a lot more primitive. 

Another aspect to this is that back then, most of the companies producing the base components made axial components, radial components that would go in a PCB were more rare, and generally speaking, of lesser quality. That's not true today. 

Depending on how a PCB board is laid out, you can have (very) small resistances that build up on a board that you wouldn't have on a PTP or turret board amp, but it's so small that no one would ever really notice. 

The main difference really is reliability. PCBs are fairly fragile, at least compared to turret boards. PTP amps can be pretty fragile too. What's great about a turret board amp is that the components are soldered in and they tend to be rock solid. Well suited to life on the road, if need be.


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## Goatroper

AldermaticAmps said:


> It's not really so cut and dry. Electronically speaking, there isn't much of a difference, but you do tend to get better quality components on PTP (or rather turret board) amps. This doesn't have to be the case, especially with what they can do with PCBs these days, but years ago, PCBs were a lot more primitive.
> 
> Another aspect to this is that back then, most of the companies producing the base components made axial components, radial components that would go in a PCB were more rare, and generally speaking, of lesser quality. That's not true today.
> 
> Depending on how a PCB board is laid out, you can have (very) small resistances that build up on a board that you wouldn't have on a PTP or turret board amp, but it's so small that no one would ever really notice.
> 
> The main difference really is reliability. PCBs are fairly fragile, at least compared to turret boards. PTP amps can be pretty fragile too. What's great about a turret board amp is that the components are soldered in and they tend to be rock solid. Well suited to life on the road, if need be.



I beg to differ on the your last paragraph. Components are soldered on the PCB board. They certainly are not glued! 
Its my opinion that the PCB board amps are more reliable and less noisy. Lead lengths are reduced so they are less likely to vibrate and crack and pick up stray inductance.
I think the PTP vs. PCB goes back to what Techs wanted.
Lets say you are a tech and say a customer asks what is a good Marshall to modify. He will tell you hands down that the PTP are better. Why? Because its so much easier to modify or fix. So after many years of techs preferring PTP over PCB, Marshall buyers are now programed to think that PTP is the way to go. I personally feel the opposite is true. JMHO.


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## SonVolt

Randall Smith has a good essay on PTP vs PCB boards. 



> Point-to-Point Wiring
> Myth VS. Reality
> 
> In the course of a recent interview, I was asked how the Trem-o-Verb gets its great vintage performance--without being wired point-to-point, and "would it be even better if it were?"
> 
> Perhaps this wasn't such a surprising question since the author had recently reviewed some pricey amplifiers whose manufacturers emphasized that their amps were indeed wired point-to-point, as if that mere fact would indicate (to those "in the know" at least) a product of precious distinction.
> 
> What Is It?
> 
> In point-to-point, the resistors and capacitors are joined with wires to solder points laid out on an insulating tag board. Wires from each solder joint then run off to the tube sockets, switches, and controls. One manufacturer has even rejected the tag board and uses phenolic terminal strips screwed to the chassis instead. This method deserves recognition for being the slowest, most labor-intensive and most error-prone wiring method of all. Point-to-point is probably about the oldest construction style and it's still appropriate for making a "one-off" piece of electronics. But does it produce a better sounding amp?
> 
> My job as designer has always been to focus on the "black magic" of amplification: first, how to get it and, second, how to get it consistently. And there, my friends, is the biggest disadvantage with point-to-point, consistency is very hard to maintain.
> 
> What We Do
> 
> From the first, Mesa/Boogies have used a combination of point-to-point and printed circuit board methods in order to ensure absolute consistent placement of critical parts and conductors. It is easy to demonstrate how moving some parts or lead wires as little as 1/4" can make a huge difference in the top end "transparency" of the sound--exactly where a lot of the magic lives--or dies.
> 
> Inside a typical point-to-point amplifier are signal wires leading from the component board to the preamp tube sockets. Because many of these can be quite critical, we always locate our tubes along the center line of a printed circuit board so the lengths of traces can be extremely short and perfectly consistent.
> 
> Great care and many scrutinized revisions result in a circuit board layout that avoids any unwanted "stray couplings" that can rob tone, or may even include a few nuances of intentional interaction (black magic) which cannot be reliably duplicated in the point-to-point style.
> 
> And Why We Do It
> 
> For example, the great top end of the Dual Rectifier has an aggressive bite but avoids the harshness by the way two very important traces are laid out on the board. One trace is on the top and the other runs right beneath it on the bottom side of the board. Thus the very small--but significant-amount of capacitance coupling these two together through the board performs a subtle filtering kind of negative feedback in a critical region where the harmonics can be made to line up just right. Obviously the alignment of the traces on both sides of the board must be precise and consistent for this to work.
> 
> Here's an illustration of the different wiring techniques. Think of printing books versus writing them out longhand. Once the type is properly set each printed page will be the same--no errors. Now go one step further and imagine trying to line up the letters on both the top and bottom sides of a sheet of paper--this time by writing longhand. It's all but impossible. Yet such precise alignment is critical to achieving the performance we're after--each and every time. With a printing press or a printed circuit board it's easy.
> 
> Where do we still wire point-to-point? Anywhere it makes a better amplifier is the brief answer. Many manufacturers try to put everything on printed circuitry, but we individually mount and point-to-point wire all jacks, switches, transformers and 8-pin power tubes. The reasons are increased reliability and total ease of replacement. If those parts are PC mounted, major disassembly is required to get at them. Even worse, they can cause the whole PC to fracture if they're bashed in hard enough, then the amp is practically non-repairable.
> 
> Our commitment is to provide a professional instrument which, with minimal maintenance, can last a lifetime or more. All our circuit boards are double-sided and "plated through" meaning that each and every hole has a platinum and copper sleeve formed inside of it which is integral with the copper traces on the top and bottom. This way each component lead is soldered three times: top, bottom and inside the hole.
> 
> Most manufacturers use singlesided boards where there is only one solder connection per part on thin foil glued to the boards surface. Moreover, these boards, once installed can't be hand-soldered for repair or replacement without totally dismantling the amplifier.
> 
> Let's Talk History
> 
> I must have repaired thousands of old Fenders--and I was the guy who could usually get rid of the stray noises--but not always. I finally found out why some of these noisy amps seemed incurable. The noise was originating in the point-to-point tag board itself! The board material can absorb moisture and become slightly conductive. The factory's recommendation was to bake the boards in a drying oven then dip them in melted wax to seal out the moisture!
> 
> Here's another: Tag boards warp, and the warpage increases the space between eyelets. Years ago, a guy phoned me, freaking out that his Fender had gone down before a big gig. I listened to his description of the problem, then advised him to pull out the chassis and look for the brown-black-brown-silver resistor running lengthwise across the board. "Give it a little tug and you'll probably find it's broken loose at the solder joint," I told him. He called back relieved and ecstatic--said that he'd never fixed anything before in his life. No sweat. I must have fixed a hundred black face Fenders where point-to-point board warpage had caused this problem. Don't get me wrong, I love Fenders. Without them, it's safe to say, none of us would be here!
> 
> Conclusion
> 
> So there you have it, four specific advantages of the printed circuit board: 1.Consistency of location, 2.Ability to use the board for intentional coupling, 3. Immunity to noise-causing moisture, and 4.It does not warp.
> 
> Now what about the way in which a conductor affects the sound? Is a round copper wire better than a flat copper trace on a circuit board? Not according to Randall Research (no relation to me!) who has studied audio conductors under all conditions, including at the molecular level under an electron microscope. His opinion is that if there is any advantage either way, it would be with the circuit board trace whose profile offers far greater surface area. It is well established that audio signals (especially the higher frequencies) tend to flow on the surface of the conductor, not through its core.
> 
> All this is not to say that there aren't great sounding point-to-point amplifiers-obviously there are. But having built lots of amplifiers both ways myself, the mere fact that an amplifier has been wired this way is, as far as I can see, a guarantee only that it will cost more. If there was an intrinsic sonic benefit to using point-to-point throughout, you can bet that we would do it!


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## Strateuphoria

AldermaticAmps said:


> Depending on how a PCB board is laid out, you can have (very) small resistances that build up on a board that you wouldn't have on a PTP or turret board amp



^ I 'feel' a difference when playing.


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## AldermaticAmps

Goatroper said:


> I beg to differ on the your last paragraph. Components are soldered on the PCB board. They certainly are not glued!
> Its my opinion that the PCB board amps are more reliable and less noisy. Lead lengths are reduced so they are less likely to vibrate and crack and pick up stray inductance.
> I think the PTP vs. PCB goes back to what Techs wanted.
> Lets say you are a tech and say a customer asks what is a good Marshall to modify. He will tell you hands down that the PTP are better. Why? Because its so much easier to modify or fix. So after many years of techs preferring PTP over PCB, Marshall buyers are now programed to think that PTP is the way to go. I personally feel the opposite is true. JMHO.



Dear lord, I never said that components were glued into a PCB board! Well, sometimes a hot glue gun is used to stabilize bigger components, but that's besides the point. 

The point with stability, is that a turret board is made of thick sturdy fiberglass. PCB's are (partly) made of the same material, except they're thin. I have seen many a broken PCB board in my day. I've never seen anyone break a turret board. Most turret board connections are shorter than they are on PCBs, since components will tend to share the same soldier point. 

I would always prefer a turret board amp, the only problem is that this becomes impossible when you get into monster amps with multiple channels.


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## Goatroper

AldermaticAmps said:


> Dear lord, I never said that components were glued into a PCB board! Well, sometimes a hot glue gun is used to stabilize bigger components, but that's besides the point.
> 
> The point with stability, is that a turret board is made of thick sturdy fiberglass. PCB's are (partly) made of the same material, except they're thin. I have seen many a broken PCB board in my day. I've never seen anyone break a turret board. Most turret board connections are shorter than they are on PCBs, since components will tend to share the same soldier point.
> 
> I would always prefer a turret board amp, the only problem is that this becomes impossible when you get into monster amps with multiple channels.



I was being sarcastic about glue. The components are soldered in place.
When you say most turret board connections are shorter, you cant possibly be talking about the components themselves, especially on a Marshall.


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## AldermaticAmps

Some connections have to be longer, but others aren't. Often in a turretboard amp, two components will share the same lug. This is as short as a connection as you can get. With a PCB, you'd run a trace instead. For instance, often the plate resistors on the first tube shared the same pin. This makes for a shorter connection.

I always prefer turret board amps. They often sound better, at least to my ear, and they're easy to work on. You have a lot of leeway in what kind of components will go into a turret board amp, with PCB amps, with radial components, the board was made for one particular kind of component, and it makes modifications a nightmare. It would be like trying to take a job as an interior decorator, without being allowed to come into the house.


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## tone seaker

PCB amps have to have the whole board removed to get to the solder underneath to change out resistors or caps. And there is not much extra length in the wires going to the board making it very difficult. Point to point you just unsolder the ends of the cap or resistor.

hard




super easy


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## Olde Growler

Well, we certainly stepped in the weeds in this one? It was our intention to establish a transition day and month for historical reasons. I did not intend to start a PTP/PCB tone or tech debate? But as we all know, threads can take a left turn or two. Their are great sounding amps and dogs on both sides of the change. 

We're looking for inspection tag dates of '73 amps both PTP and PCB to put together a baseline of the transition. If you have a '73 amp, please feel free to post pics of tags, style boards and serial number date codes. If you have a '74 amp that is PTP, even better. 

Thanks for your help. OG


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## Jucciz

To the original question: late 1973, I would say. I did some research based on my personal experience as well as what can be found in amparchives.com.

I have a '73 50-watt JMP Tremolo, serial number T/A 5967E. I've understood that every serial number was used only once each year regardless of the prefix - meaning that there won't be a S/A 5967E, because there is a T/A 5967E. The inspection date in my Marshall is September 11, 1973, so at least some amps inspected in early September 1973 were still hand-wired.

Pictures here:
https://www.dropbox.com/sh/45yjxzf8w6d9izy/W1571p6KvC

On to amparchives.com and we'll see that There's a 100-watt Super Lead with the serial number SL/A 6121E, and it has a printed circuit board (PCB). The inspection date is September 17, 1973 - just six days after my T/A 5967E. The difference is 154 amps.

Amp Archives/Marshall/100 Watt Series 1965-1981/1959 Super Lead 100W/73 1959 Super Lead 100W SN SLA6121E

One could imagine that somewhere around that time the change took place. Correct me if I'm wrong.


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## NativH

Olde Growler said:


> That is what I understand. I was looking to see if their was a specific month on the inspection tags that we start to see the transition for at least the Super Leads and Super Basses.


 Only a single data point, but my '73 PTP SL (1227E) date is 10-1-73 (January 10, 1973). Yeah, I know the 7 in '73 looks like a "1" but it isn't. Believe me.


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## janarn

Super PA's did not change to PCB,
so you will find Super PA's from '74 (and maybe also '75) with PTP.


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## tone seaker

NativH said:


> Only a single data point, but my '73 PTP SL (1227E) date is 10-1-73 (January 10, 1973). Yeah, I know the 7 in '73 looks like a "1" but it isn't. Believe me.



are those tags like speaker and pot codes where the numbers are backwards? I would not think so making yours Nov. 1, 1973


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## NativH

tone seaker said:


> are those tags like speaker and pot codes where the numbers are backwards? I would not think so making yours Nov. 1, 1973


I don't think so but I'm open to suggestions. With a serial number of 1227, it should be very early in the series for that year. Of course Marshall could have started it early in the year with an early serial number, set it aside, and completed it late in '73 putting a November completion sticker on it. But then again, I never heard of a '73 SL being PTP as late as November. But we are talking about Marshall back in the good old days here.


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## Jucciz

tone seaker said:


> are those tags like speaker and pot codes where the numbers are backwards? I would not think so making yours Nov. 1, 1973



In England they used the date format DD-MM-YY (just like here in Finland), so 10-1-73 surely is January 10, 1973.

Here's my Marshall JMP 50-watter from 1972:
https://dl.dropboxusercontent.com/sh/g7gllxhmx12zjnt/AACVBG-CNXMW0-s6KWehjzSka/DSC_2971.jpg

The date code is 13/3/72. I'm pretty sure there wasn't a 13th month in any year.


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## Appetite4distortion

Here in Europe we say the same about USA date format MM-DD-YY .."oh man, see, they write'em backwards.."

Yes, everything Marshall did was coming from UK, and UK is using Gregorian DD-MM-YY, "little endian format" (from smaller to bigger), common to the vast majority of the world's countries.


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## tone seaker

Appetite4distortion said:


> Here in Europe we say the same about USA date format MM-DD-YY .."oh man, see, they write'em backwards.."
> 
> Yes, everything Marshall did was coming from UK, and UK is using Gregorian DD-MM-YY, "little endian format" (from smaller to bigger), common to the vast majority of the world's countries.



Like metric


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## sct13

Just for fun....which sound better "Rosemary" or "Sheila" I have both....

Srsly mid 73' depends when the components ran out and when the new design change parts got there on the floor. In manufacturing speed and consistency is a major factor in any situation. I am one of those do it yourselfers I can fix anything....except some crazy, complex, muti layered, solder happy, impossibly small component board (that WILL become brittle with age and heat) so I vote PTP all the way. True about longer leads acting like antene, but what the hell, wouldn't be a Marshall if you couldn't get some RF noise. Harley's leak oil....


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## Olde Growler

Anymore '73's Super Leads or Super Basses pics? Please post. 

Thanks!


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## gldtp99

I recently picked up an inop 1973 Super Lead with a 6/6/73 date code on the inspection tag----- It is a turret board amp and the board looks to be all original---- Mustards in place and the factory dye on the solder joints.
The PT has one endbell removed along with the mounting bolts----- thankfully the endbell, mounting bolts, and mount reinforcements were in an old plastic bag supplied with the amp.
No pics yet but I'll get some when I get time to start this project---- It might be a little while............................. gldtp99


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## Olde Growler

Great! Looking forward to the pics.


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## gldtp99

Olde Growler said:


> Great! Looking forward to the pics.















My 1973 Superlead tag and gut shots---- now for the rest of the story (PT looks to be hurting):









I'll get time to start on this project one of these days---a Superlead rescue project and no, this one won't be modded like the rebuild/mod job that I did on a local player's 1979 Superlead earlier this year (vid below)----- I posted about this "came to me butchered and inop/modded" 1979 Superlead in another thread..................... gldtp99

https://www.youtube.com/watch?v=zog4b7jkq74


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## sct13

Just curious, Whats the serial number on this, that handwritten date may not be an accurate build date. the metal face places this 1969 and after, but some of those components are older. Like that Hunts cap....I'm no expert, just curious what the date code is.


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## gldtp99

sct13 said:


> Just curious, Whats the serial number on this, that handwritten date may not be an accurate build date. the metal face places this 1969 and after, but some of those components are older. Like that Hunts cap....I'm no expert, just curious what the date code is.



This amp has an "E" date code----- 1973

The filter caps were made by Plessey and have a 73.04 date code which makes sense with the 6/6/73 date on the inspection tag.

If you're talking about that rainbow colored cap on the Presence pot (is that the Hunts ?) I have no idea what that is about, I figure it's probably a replacement done long ago----- or is it possible that it is stock ?


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## sct13

Well, its a 73' then....I was referring to the big red one on the end, My 68' has two like that. they say "Hunts" on mine. The rainbow, or "Tropical fish" ? I forget who did those. I have allways seen Mullards or phillips on the presence pot. 

Have you checked the pot codes? 

I would love to get my hands on something that cool. Project time!


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## SonVolt

So a JCM 800 2204 has a PCB?


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## AlvisX

SonVolt said:


> So a JCM 800 2204 has a PCB?



Correct


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## Olde Growler

Thanks gldtp99! This helps with my question. The amp is dated 6/6/73. Same day as D-Day. Looks like the PT has been through a war? I would love to find one to restore just like it. GLWTR. 

OG


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## AlvisX

Small phone cam pic of a late 73 I rescued from a guy in AR a few years ago 





I got it home ,plugged it in ...fizzzzzzz,wheezzzzze,spikey ...every horrible sound you can imagine .....He advertised it with "new tubes" ....apparently they had no "new" bias . They were runnin about 5w apiece at idle 
Had quite a few burned traces & sloppy (not bad) cap job
I got my hands in it ...changed it to a shared cathode ,did a little brite cap tweak,biased it to rock, Lar-Mar Post Phase Master! 
Now sounds like the almighty. I cant get enough of this amp. It's the white head in my avatar


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## fender101punk

Picking up a mint '73 50w Lead Canadian export model this Friday. All original including all of the tubes. Haven't seen a gut shot but I'll take one and post it on Friday. Serial number 6267E and dated 25-9-73. Rosemary signed


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## sct13

Would be Very interested, I have a late 68/ early 69 of the same.


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## usednabused

there should be a ROSEMARY thread or page! with all the details on her and the amps she signed!


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## Olde Growler

Joan does not do bad work either!


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## fender101punk

Heres a gut shot of my September 25th 1973 50w


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## 3Pickup

I have a 1974 Super lead 100 ( white tag inside dated 73 ) Just did a side by side comparison with my 200? SLP 1959 I guess hand wired and the 74 was just a tad brighter sounding and alittle more raspy sounding, both on 10 thru a 100 watt cab, not a thing wrong with a non hand wired head, sounds fantastic.


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## stratjmp

I have a December 1973 superlead...pcb. I like this amp but it does not sound as good as my 1972 jmp 50. I also have a 72 superlead which sounds night and day diff to the 73. The 73 i have to jump the channels to get a thick sound and the 72 is darn near too dark in the bright channel but sounds awesome at ear bleed levels when the treble comes alive.


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## Olde Growler

Are all the tubes the same type?


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## stratjmp

Theyre older groove tubes but i have swapped jj's in it before to see if that was an issue...its just the nature of the amp prob. My 72 superlead has a sb serial and has lead taped over bass on the back panel from the factory but it may still have the bass circuit in it whick may make it darker. I have heard of them doing that.


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## Joshabr1

For the people who argue that they can tell a difference between a pcb and a turret board amp with the same exact components, tubes, transformers,filtering I call bullshit. The amps are so different one from another that the whole premise is not really a aurguement to me. I have both types with very similar components and I also have good ears and their is not a damn dimes worth of difference other than they are all a little different anyway. The drawback to the pcb and the only one to me is if u like to tinker a little they are way more difficult to get into. Other than that I think the late 73 early 74s are the best value in the whole market. I have a jan 74 that I turned in to a bass preamp with lead specs elsewhere and I would put it against any turret board amp I have ever owned. We should spend more time playing and sharpening our skills and less time worrying about these things. Me included


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## shermanpup

Olde Growler said:


> I understand that Marshall switch from Point to Point to Printed Circuit Boards in 1973. What month in that year did they start producing PCB Marshalls?


I have a 1972 Marshall according to the serial # check, and it has a PCB ,so either the serial # people are wrong , or the info in this post is. This amp has a early Metaltronix mod . I don't like the mids rotary switch , but other than that, this amp kicks ass . It is the same amp as the Paul Gilbert model that Kemper sampled. Sorry for posting on an old thread, but I wanted to put it out there


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## neikeel

Exojam said:


> It just cannot be in my opinion.





shermanpup said:


> I have a 1972 Marshall according to the serial # check, and it has a PCB ,so either the serial # people are wrong , or the info in this post is. This amp has a early Metaltronix mod . I don't like the mids rotary switch , but other than that, this amp kicks ass . It is the same amp as the Paul Gilbert model that Kemper sampled. Sorry for posting on an old thread, but I wanted to put it out there



Very interesting as I've never seen a pcb before '73 (the first ones were an odd pale colour (some yellowish and some a pale green) following on from the cream turret boards.
Can you post pics of your serial, inspection tag and the board as it is an important reference point for those of us that thought we knew better.


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## ampmadscientist

shermanpup said:


> I have a 1972 Marshall according to the serial # check, and it has a PCB ,so either the serial # people are wrong , or the info in this post is. This amp has a early Metaltronix mod . I don't like the mids rotary switch , but other than that, this amp kicks ass . It is the same amp as the Paul Gilbert model that Kemper sampled. Sorry for posting on an old thread, but I wanted to put it out there



How's the weather in South Bend?


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## Ned B

The earliest PCBs I have seen were on a SL and Artiste combo both dated May '73, An interesting amp I saw on Ebay some years ago was a MKII SL USA model with 12/73 inspection date, 6550s, copper choke, but PTP circuitry. A friend of mine has a CMI 2X12 PTP combo from '74. I don't believe there were ever any PCB Tremolo or PA boards, but those models were pretty discontinued by late '73/early '74.


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## Jeff West

Hi Ned- Hope your amps haven't been freezing solid in Chicago!

Thought I'd kick in on this thread that for 23 years I've had SA 6849E 50W 1987. The inspection tag is dated "17/10/73" and stamped "50W LEAD M992 USA". It's of course an export model, with polarity switch and hard wired for 117VAC.

It reportedly had been in storage for a long time when I got it and was quite pristine. Was thought to "not work" since it wouldn't make a sound, but turned out to have a bad connection at the output jack- has worked great ever since, once that was re-soldered, original Daly filters and all. So well worth $235.00 at the pawn shop on Airline Hwy!

This one is early PCB. It has most of the "Mark II" circuit changes, inc in this case stock 82K bias feed Rs (!), big square RS .68 presence off of 4ohm tap, but does not say "Mark II" on the back or anywhere. Interestingly, it came with I believe all original tubes, and these included big bottle RCA branded 6CA7/EL34s. I'm pretty certain it was stock with EL34s, IIRC has the 220K in the bias circuit not 150K, and defintiely will not bias most any pair of 6550s. From what I've seen, the "MK II" circuit changes mostly were done starting late '73, but were first done independent of switch to 6550s, unlike what is sometimes assumed. For example, I know of original owners of '73-'74 1987s in Japan that are like this, but never came stock with 6550s there at that time (so I'm told).

The earliest 1987 I've seen that is labelled "MK II" on the back was very early Jan 1974, and I think it did have 6550s. Anyone have an earlier sighting?


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## Ned B

Hi Jeff are you still in Memphis? I remember a late '73 SL with 6550s I saw that had a MK II decal added which I assumed had to be the beginning of that phase. It seemed that MKII coincided with the switch to 6550s for the US exports.


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## Jeff West

Hey Ned- No, my wife and I were heavily recruited to relocate to Houston, and I've been here since 2011. It's worked out well. We still get back to New Orleans a lot.

I realize I was assuming that you were still in Chicago!

Yes, that seems right about the MKII labelling, but some of the small circuit changes may have been started or at least implemented independently of 6550s, I guess. Was that one _very_ late '73?

Are you still using the metal base EL34s in anything?!


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## Ned B

12/73 for sure. I saw that one in person but didn't see inside to know that it was PCB but I would assume so. The other one on ebay also 12/73 and MKII though printed, not a decal, was PTP, an interesting combination of features.

I still have those very early EL34s (1957?) unused in the box. Do people even talk about that era of EL34?


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## Jeff West

Interesting, so I guess you really could find many different combinations throughout the period May to December ‘73.

What I would be interested in would be what the specifics of the original circuit were in that 12/73 pro MkII, the presence, bias feed Rs, etc?

The Eindhoven metal base EL34s are cool and sound good in Marshalls IMO, I still have some, but would be an increasingly challenging interest to start pursuing these days . . .

PS: the above was meant to say "in that 12/73 PCB MkII"


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## Ned B

I believe the NFB resistor changed to a 100K in '73 as well as the presence with less negative feedback. The 2nd .68 was gone in '72. B+ was getting pretty low by that point. I think I have a photo of a very strange one-off '73 circuit I can upload here.


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## Jeff West

Cool. My Oct '73 fits your above description, except for B+. Xf2s idling at about 32-34ma in it usually show about 438-442V on the plates with reasonable wall voltage. I know some 1987s were a lot lower than that.


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