Marshall Major 1967

[tubenit]

Trying to come up with a legible Marshall Major schematic.  The original was VERY difficult for me to read some of the values on. And I think how Marshall drew this up complicated reading the schematic.

Once I get this verified and/or corrected, then I plan to post a couple of mods reported to be good with this amp.

IF someone would look over this & offer edits or a thumbs up,  I would be appreciative.  I am attaching an editable SCH version if someone wants to use that for edits and corrections.

NOTE the atypical  phase invertor topology ................ never seen anything quite like that before?  Not sure about the values in that areas of the schematic at all?

With respect, Tubenit 

EDIT:  will repost corrected schematic thanks to Silvergun's edits

[SILVERGUN]

I need some practice with Express SCH so I took a couple minutes and made a couple adjustments based on what I think I see on the original schematic.
These are the changes to look for from your original:
- Changed input fuse value to 10 amp
- Added 2.7K resistor to cathode of V2 in series with 100K (even though I don't understand why it's there)
- Moved junction of .02 coupling cap and 1M resistor feeding grid of V2 pin 7 (moved pin # also)

[Willabe]

Doesn't the 1M go to ground and the coupling cap go to the 2.7K/110K junction on V2? Makes a concertina PI to feed the 2 driver triodes.

Nope, just looked at the schemo.


                Brad   

[tubenit]

Doesn't the 1M go to ground and the coupling cap go to the 2.7K/110K junction on V2? Makes a concertina PI to feed the 2 driver triodes

.

That sure would make sense to me!

Brad,  I am thinking your probably right, but it sure doesn't look that way on the original?????  I am puzzled by it.  Maybe just a mistake on Marshall's original?

http://el34world.com/charts/Schematics/files/marshall/Marshall_major_1967u_lead_200w.pdf

Hey, I just found this ............... Brad, you are right on!!!  Good catch!!    The 270R in the Major schematic should be 270k also!!

http://www.drtube.com/schematics/marshall/200w.gif

With respect, Tubenit

[SILVERGUN]

Here's a big snip....

[tubenit]

I think Brad is correct !!!!  This schematic makes more sense to me.

Take a look at this off the DR. Tube site.

http://www.drtube.com/schematics/marshall/200w.gif

Tubenit

[SILVERGUN]

Hey, I just found this ............... Brad, you are right on!!!  Good catch!!    The 270R in the Major schematic should be 270k also!!

WOW!
 

They repeated the mistake on this schematic as well:
http://el34world.com/charts/Schematics/files/marshall/Marshall_major_1966_200w_pa.pdf

And this one:
http://el34world.com/charts/Schematics/files/marshall/Marshall_major_1978u_bass_200w.pdf

NICE WORK BRAD!

[Willabe]

I just looked in TUT5 in the Marshall Major chapter (7) and it's drawn like the schemo that tubenit just posted.

It's a bootstrapped concertina PI driving to triodes, 1 for the push side and 1 for the pull side of the KT88's.


                  Brad   

[Willabe]

That PI made no sense to me either, I kept looking at it thinking I was missing something because of the way it was drawn, but it was drawn incorrectly.        


                      Brad     

[tubenit]

CHECK out the great Marshall Major tone ................

OK, I am thinking that cranked tone of the Major with the OWM (one wire mod) and PPIMV (post phase invertor master volume) that is in this video thread:  http://el34world.com/Forum/index.php?topic=17530.0

................. is probably something pretty similar to one of these schematics.

With respect, Tubenit

[Ritchie200]

Yes, there needs to be grid leak for the cathodyne.  There were several mistakes on the original drawing.  It has been so long, I can not remember them all...  I do remember the phase inverter issue and one in the power supply - but there were several.  Plus, there were undocumented changes over the years that are not reflected in any drawings.  I am totally swamped right now, but I will dig out my marked up schemo in a day or two and share.  One necessary upgrade is to change the screen resistors from 220 or 250 5 watt (they came with both) up to a 1K 10watt.  It will be a heck of a lot more stable.  I can recommend a great surface mount if anyone is interested.  The original 220/250's were these big doorknob resistors.

Jim

[tubenit]

change the grid resistors from 220 or 250 5 watt (they came with both) up to a 1K 10watt.

I am presuming you mean the screen resistors?  Correct?

With respect, Tubenit

[SILVERGUN]

I am totally swamped right now, but I will dig out my marked up schemo in a day or two and share.

You've got me shopping for KT88s,,,,so it's the least you can do. 

[Ritchie200]

change the grid resistors from 220 or 250 5 watt (they came with both) up to a 1K 10watt.

I am presuming you mean the screen resistors?  Correct?

With respect, Tubenit

What? what?  SG did it! 

Uhh, old age alert...
Jim

[Ritchie200]

SG, No doubt you will have this thing breadboarded by 10:30am tomorrow morning!  You amaze me!

Jim

[sluckey]

Hey Sluckey,  IF you read this can you confirm that this makes sense to you also, please?

The PI and driver looks good.

There's something missing in the bias winding.

[DummyLoad]

Hey Sluckey,  IF you read this can you confirm that this makes sense to you also, please?

The PI and driver looks good.

There's something missing in the bias winding.

got my attn. too: bias winding...maybe it should be a FWB with the (+) side grounded?

missing connection between 200uF series stack & 56K series stack.

diff-amp grid-leaks should be 270k? i'd use 470K. just because. :p

missing dot on 1M grid-leak of cathodyne and 2.7K Rk and 100K split. schematic shows jump and no conn.

looks exceedingly ice pick-ish likely just before near total hearing loss... unless you play bass, why?

flyback diodes across OT 1/2 primaries would probably help considerably. why not just run pentode mode and pull screen B+ off the floating CT. should be about 325V after more smoothing around 300V...of course, with fly-back diodes as well. you still get 100W/pair plus you don't need as much drive signal.

edited the 1967 model schema - probably more to the tune of what most here would build: a 1959 front-end with the major power amp?

--pete

[tubenit]

Thanks gentlemen!  I appreciate the help.

I am not sure what you guys are saying regarding the bias control??  Can you offer a little more explanation about that & I'll correct it in my schematic and repost then? 

I am also wondering how close KT66 tubes are to KT88 tubes in tone?  Anybody know?

with respect, Tubenit

[sluckey]

This schematic shows the missing center tap for the bias winding...

[tubenit]

EXCELLENT!   Thanks for the help, as always!!   Will edit the schematics and repost later today (hopefully).

Best regards and respect, Tubenit

Someone offered me this response also (below):

One mod you should do while its open is to buss all the output tubes Cathodes down and run it into a inline fuse as the HT fuse is too slow to respond to a shorted output tube and then the OT goes south!

[tubenit]

Jim,

I'd love your best educated guess on something .............................

Q1:  IF you built the Major with only two KT88's (using the one wire mod and PPIMV), what is your best guess on the
       percentage of the essence of the original Major tone that you could preserve?  (example:  like 93% of the essence
       or  87% of the essence of the tone, etc......)

Q2:  IF you built the Major with only two KT66's and then did cathode biasing, what is your best guess on the percentage
       of the essence of the original Major tone that you could preserve?   Maybe 75%?? or what ????
       
        I am betting a nickel that it would be a fabulous sounding amp, but it may be far enough away from the original   
        KT88 Major tone to not be considered still in the ballpark of the Major tonewise?

To add some clarity, what I am asking is playing the Major at home ............... that "playing at home tone" being the standard of reference  in this discussion vs.  all 200 watts cranked to "11" with ear bleeding, pants flapping, tornadic force of a sunami wall of tone.
 

And before you go saying that less than the full force of 200 watts of cranked KT88's is heresy, ....... I do remember that you yourself have built cute little Firefly amps.
 

With respect, Tubenit
       

[sluckey]

Why not take it way on down? Maybe a pair of 6AQ5s? Call it Major Minor. 

[Mike_J]

Does anyone know the HT and screen voltages that were used on this amp?  Do you think there is room for the Sluckey inspired Plexi/800 circuitry with dual tone stacks, active fx that can be switched out of the signal path, the one wire mod and PPIMV?  I think two KT88s would be appropriate for this build unless you need more than 490 volts for the KT88s.  Would like to know the answer to Tubenit's Q1 in reply 20 above though before a final tube count would be established.

I really liked the tone coming out of that video.  I would like to have one of those.

Thanks
Mike

[tubenit]

Why not take it way on down? Maybe a pair of 6AQ5s? Call it Major Minor.

Jim,

Hey, it was Sluckey that said that not me!     

I only thought it was a really great idea before he posted it (all the way down to the same name of Major Minor.)
Sometimes great minds think alike!

With respect, Tubenit 

[SILVERGUN]

To interject, hopefully without being too much of a distraction,,,I offer this:
- The 'unique' driver stage came into question when I was messing around with the SSS
- Some of the guys were questioning the value of that driver, and if it would be 'needed' if you were only trying to drive 2 output tubes and not 4
- My personal experimentation led me to feel that there was a valuable quality in the 'tone response' that was generated by that stage,,,and that it is worth using for that reason alone.
- IMO, I feel that the combination of that driver stage, pushing KT88s at high voltage into a UL OT is the foundation of the essence of why this amp sounds different than more commonly built marshalls

why not just run pentode mode and pull screen B+ off the floating CT. should be about 325V after more smoothing around 300V...of course, with fly-back diodes as well. you still get 100W/pair plus you don't need as much drive signal.

Will that change the 'character' of the output stage?.....what effect?

[jazbo8]

Does anyone know the HT and screen voltages that were used on this amp?  ...unless you need more than 490 volts for the KT88s. 

A lot higher, based on people that have worked on the amps, the B+ is well over 600V, and depending on the mains voltage perhaps over 700V. No modern tube could survive such abuse without making some adjustments, also part of the sound is also due to the use of an UL OPT. It's quite a different beast compared to the typical Marshall designs.


Here is an interesting article on the Majors.

[tubenit]

Here is an interesting article on the Majors.

That is an interesting article!  I'm sort of thinking now that 6AQ5's may not be the most optimal tube for 650 volts? 
 

Seriously, I am wondering about the idea of a pair of cathode biased KT66, one wire mod and PPIMV?  And not using a UL output transformer?  I wonder how close that might emulate the Major sound in that YouTube?

With respect, Tubenit

[Mike_J]

Does anyone know the HT and screen voltages that were used on this amp?  ...unless you need more than 490 volts for the KT88s. 

A lot higher, based on people that have worked on the amps, the B+ is well over 600V, and depending on the mains voltage perhaps over 700V. No modern tube could survive such abuse without making some adjustments, also part of the sound is also due to the use of an UL OPT. It's quite a different beast compared to the typical Marshall designs.


Here is an interesting article on the Majors.

jazbo8

Thank you for the reply.  I read a few things about the 1967.  Seems that Richie Blackmore of Deep Purple fame had the preamp cascaded so the 1967 was Marshall's first master volume amp.  Therefore, the Sluckey idea would definitely work.

I am not 100% sure but it sounds like they started to have the problems with the tubes and the output transformers frying when they increased the voltage on the KT88s from the 480 to 620 volt range and overdrive pedals were being added to the signal path.  Not sure if that is when they went to the ultralinear OTs or not but would like to know if anyone could enlighten.  I would like to know the difference in tone between an amp with say a Plexi OT at 480 volts versus the ultra linear OTs that were used.  Guess I need to look up the specs on four KT88s to see what ohm rating they require.

As I recall this is the amp SRV used before the SSS but had to quit using because he couldn't find matching quads of KT88s at the time.  He used it for his clean tones.  After that the SSS filled that role.

Hope this reply isn't off track.  I sure would like an amp that sounds like the one in that video.

Thanks
Mike

[SILVERGUN]

Jeff,
I know you are one to appreciate original thought, so here's one for ya...(not sure how original, and maybe the amp in the demo was done this way??)

'What if' we placed the PPIMV between the phase inverter and driver tube?

So that with distortion added in the preamp, we wouldn't be overloading the grid of those driver triodes...

This comes from some of my experimentation where I was getting an unfavorable sound by adding distortion to the preamp of the SSS

[sluckey]

Hey, it was Sluckey that said that not me!

Should be OK. I play a Strat and know the cords to Lazy!   

[Willabe]

SRV used them for his clean sound.

Also the tone stack is simi-active because it is in the -FB loop. This is part of this amps sound. But there comes a point when getting close to diming the amp that the -FB loop can't keep up and drops out.

KOC, TUT5, 7-5 , Marshall Major chapter;

"Dialing the EQ up or down introduces an "error" in the transfer function of the amp, which FB tries to correct. At some point it cannot, the loop decouples electrically, and the amp distorts. Before that point, the speaker output has been altered from looking identical to the input, to being something different but still useful."


                   Brad         

[Willabe]

'What if' we placed the PPIMV between the phase inverter and driver tube?

KOC, TUT5, 7-6 , Marshall Major chapter;

"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.


                           Brad   

[SILVERGUN]

'What if' we placed the PPIMV between the phase inverter and driver tube?

KOC, TUT5, 7-6 , Marshall Major chapter;

"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.


                           Brad   

Good point......so much for original thought 

[Ed_Chambley]

The difference in tone between KT66 and KT88 is Major.


Speaking of the clean tone only since usually distortion is created in the preamp in Marshall designs, the difference is quite similar to the difference between 6V6 and 6L6 except more pronounced.  KT66's produce a very balanced tone from bass to treble and has strong upper mid which is referred to as chime or sparkle the KT88 is the opposite.  While it does have a great upper mid the same as the KT66, but the KT88 has such a strong bottom the sparkle is not readily as noticeable.


Running both hard the KT66 would be a framing hammer hitting the chest, whereas the KT88 would be a 2 pound hammer.  The difference is readily noticeable since it has much more bass extension.


I wired the OT both ways and UL provides a much more fluid, smooth feel.  Problem is it can be rigid feeling according to the transformer.  I prefer the Dynaco replacement UL over the one Hammond sells and I have used both.  The last one I built I used a a complete set from triode here:
http://triodeelectronics.com/mk3trbuwfrch.html


Using this set with KT88 and SS rectification will put loaded plate voltages 560v, but with KT120 it drops to 520's.


I like this best so far.  The Hammond 1650R is used weighs 12 lbs and is very stiff and the 1650N will get hot if cranking the amp, but it has a better feel.


I have a jtm45 that originally ran KT66 and I switched it to kt88 because I have quite a few of the tube.  The only difference I noticed running at lower voltages is you need to brighten the amp up at lower volume.  Tweaking would take care of it as jtm45 can be dark anyway.


A LarMar PPMIV is great as it seems to simply decrease headroom.  I use Gold Lion Chinese KT88 and they hold up well and they sound really nice.  If you want to keep the power section clean and full and jangley the KT120 work fine, but if you want to get the power tubes distorting (be in another room) the KT88 are by far the best choice as the distorted tone of the KT120 is very harsh, but they will deliver the best clean signal and react very well to pedals and preamp overdrive and an even stronger bottom end.  Think killer metal.


All of these experiences are with a driver 12Ax7 and no negative feedback.

[Mike_J]

For a master volume control couldn't you just put a 1MA pot between the wiper of the treble control and the input to the PI (the .02 cap)?  Hopefully that wasn't mentioned and I just didn't understand that it was mentioned.

Thanks
Mike

[SILVERGUN]

For a master volume control couldn't you just put a 1MA pot between the wiper of the treble control and the input to the PI (the .02 cap)?  Hopefully that wasn't mentioned and I just didn't understand that it was mentioned.

It's just another way of saying what Brad posted here from TUT

"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.

[SILVERGUN]

The difference in tone between KT66 and KT88 is Major.
...
All of these experiences are with a driver 12Ax7 and no negative feedback.

Good stuff Ed, all good info....

What made you go with the 12AX7 in the driver spot?.....did you rule out the 12AU7 early and then just stick with it?

I also like what you wrote about the UL OT combined with the KT88....again, I think that's some of the magic that Jimbo is experiencing 

[tubenit]

As I am reading this, it sounds like the KT88 perhaps would be the truest tone even with two tubes?

I can not tell if the UL OT is critical from what I am reading.  Sounds like it's a factor but not critical? So, I am thinking you can "reasonably" capture the Major sound without the UL OT.  Is that correct?

It sounds like the PPIMV is the preferred master volume of the 3 mentioned?  Option #1 is the better?

I am not sure what Silvergun was actually suggesting, but I drew up what I thought he might be suggesting?  SG, feel free to correct the drawing and repost if I am not understanding you?

What about the idea of a pair of KT88 that is cathode biased with each having their own resistor and electrolytic cap?

I am trying to think of how to get reasonably that tone in the YouTube without 200 watts of power tubes. And instead have it be more like 60-80 watts?

With respect, Tubenit

[Willabe]

Option #3, not between the treble pot wiper and the .022 coupling, replace the 1M grid leak R at pin 7 with a 1MA pot.

If you go with option #1 (PPIMV) you can get the pre to slam the concertina and the paraphase driver triodes, more small bottle distortion. 

              Brad   

[Willabe]

For a master volume control couldn't you just put a 1MA pot between the wiper of the treble control and the input to the PI (the .02 cap)?  Hopefully that wasn't mentioned and I just didn't understand that it was mentioned.

It's just another way of saying what Brad posted here from TUT

"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.

No, see reply #38. MV pot between the treble wiper and the .022 coupling cap will effect the tone (thin it out) as you dial the MV down.

"Note that placing the (MV) dual pot between the concertina and the paraphase (driver triodes) stages is no different than the single-section pot at the input of the concertina (in place of the grid leak R). This is because the concertina is not a gain stage and should not be considered as such.

                    Brad     

[SILVERGUN]

I am not sure what Silvergun was actually suggesting, but I drew up what I thought he might be suggesting?  SG, feel free to correct the drawing and repost if I am not understanding you?

You got it....that was my suggestion......I was trying to have a good idea 
I like your first example - Option #1

I guess that the 12AU7 can take a big input signal due to the bias point/ high plate V,,,so you shouldn't have to worry about my concern about dropping some signal before it gets there. (Brad's terminology of 'slamming' it sounds good to me  )

I am trying to think of how to get reasonably that tone in the YouTube without 200 watts of power tubes. And instead have it be more like 60-80 watts?

I'm not sure that that specific tone is 'all that special"....it's definitely very cool, but is mostly based on preamp distortion...
So, I'm thinking that I agree with you that the UL OT shouldn't be the determining factor...(for capturing that demo tone)

IMO, you're getting pretty close with what you're envisioning.
I've got a 4.2k pri K OT here that I can try with 2 KT88s when I can get around to it....560V(ish) plates like Ed mentioned.

I also guess that cathode biasing becomes more of a heat issue at higher power due to increased dissipation, which partially would explain why it is shy'd away from.

[Willabe]

I'm not sure that that specific tone is 'all that special"....it's definitely very cool, but is mostly based on preamp distortion...
So, I'm thinking that I agree with you that the UL OT shouldn't be the determining factor...(for capturing that demo tone)

I wired the OT both ways and UL provides a much more fluid, smooth feel.  Problem is it can be rigid feeling according to the transformer.  I prefer the Dynaco replacement UL over the one Hammond sells and I have used both.

                          Brad   

[SILVERGUN]

No, see reply #38. MV pot between the treble wiper and the .022 coupling cap will effect the tone (thin it out) as you dial the MV down.

I understand 100%...
I was trying to simplify it for Mike J and show him that a similar solution was suggested by TUT in your previous post

The 1m pot would 'become' the grid leak R

[Ed_Chambley]

The difference in tone between KT66 and KT88 is Major.
...
All of these experiences are with a driver 12Ax7 and no negative feedback.

Good stuff Ed, all good info....

What made you go with the 12AX7 in the driver spot?.....did you rule out the 12AU7 early and then just stick with it?

I also like what you wrote about the UL OT combined with the KT88....again, I think that's some of the magic that Jimbo is experiencing 

SG, I tried a lot of driver tubes and I thought I would prefer an 12Au7 and it is fine for bass.  Speaking of power sections only.  It seems the preamp and tonestack of this particular amp (apples to oranges) prefers a 12Ax7  You know me, I had to try everything that would fit into socket.


If I were simply trying to get the best clean tone from the PA, then it is a 12At7.  The 12Ax7 is clean, clean, clean with the Treble and Bass at high noon.  Where the difference is the amp distorts nicely when you add Treble and Bass, but the lower the gain is in the driver tube the less there is.  I am to stoopid to know why.    That is why I just have to try it because I have never been able to get it to sound good on paper.


I have used a Leslie 147 amp with cathode bias running KT88, but a different amp again.  Nothing seems as clear and I got a lot of mushy sounding bottom in comparison.  I probably did not do it correctly because the tubes had a shorter life, but then again apples to oranges.  The NOS tungsol 6550 is probably a stouter tube than the Chinese Gold Lion KT88 even though the KT88 is rated for higher voltage.

[SILVERGUN]

ED,
Good answer...again, all good stuff... 

The more I get you to say the more info there will be for T to make his decisions 

[jazbo8]

I'm not sure that that specific tone is 'all that special"....it's definitely very cool, but is mostly based on preamp distortion...
So, I'm thinking that I agree with you that the UL OT shouldn't be the determining factor...(for capturing that demo tone)

I wired the OT both ways and UL provides a much more fluid, smooth feel.  Problem is it can be rigid feeling according to the transformer.  I prefer the Dynaco replacement UL over the one Hammond sells and I have used both.

                          Brad   

UL OPT changes the output tubes' characteristics, so it definitely has an influence on the sound, but I agree, in the Youtube clip, it's more about the preamp distortion, since I think that the amp was no where near full power during the recording, so the power tubes distortion was not really that big a factor.

[DummyLoad]

To interject, hopefully without being too much of a distraction,,,I offer this:
- The 'unique' driver stage came into question when I was messing around with the SSS
- Some of the guys were questioning the value of that driver, and if it would be 'needed' if you were only trying to drive 2 output tubes and not 4
- My personal experimentation led me to feel that there was a valuable quality in the 'tone response' that was generated by that stage,,,and that it is worth using for that reason alone.
- IMO, I feel that the combination of that driver stage, pushing KT88s at high voltage into a UL OT is the foundation of the essence of why this amp sounds different than more commonly built marshalls

why not just run pentode mode and pull screen B+ off the floating CT. should be about 325V after more smoothing around 300V...of course, with fly-back diodes as well. you still get 100W/pair plus you don't need as much drive signal.

Will that change the 'character' of the output stage?.....what effect?

i have no idea how much. probably some. one can only speculate without experimentation. there's only one way to really find out: modify the real thing, unless you can cobble together an exact or near exact copy.


--pete

[HotBluePlates]

Tubenit:
The 270Ω grid leaks for the differential amplifier stage (the one between the split-load inverter and the output tubes) must be a typo in the original schematic. If the "270" in the schematic is correct, then they must be 270kΩ. Otherwise, they'd severely load the split-load's output.

[Willabe]

The 270Ω grid leaks for the differential amplifier stage (the one between the split-load inverter and the output tubes) must be a typo in the original schematic. If the "270" in the schematic is correct, then they must be 270kΩ. Otherwise, they'd severely load the split-load's output.

You forgot to change the drawing.


                 Brad   

[SILVERGUN]

You forgot to change the drawing.


                 Brad   

Who gave this guy coffee today?
 

Thanks for sharing that TUT stuff today sir...very helpful!

Schemo looks great T!
I look forward to a break in my schedule when I can give this some attention.