Marshall Major

[tubenit]

A great sounding video posted (at the start of the thread) by Ritchie200 inspired some excellent discussion on this amp.
http://el34world.com/Forum/index.php?topic=17548.50

It should be noted that the original Marshall schematics of the Major had numerous errors!

I think a two tube KT88 version with OWM (one wire mod) and PPIMV would sound good.

Pete posted a version that he likes:

a) up the values of the coupling and bypass caps on the ice-pick channel.
b) adding cathode fuses for each KT-88.
c) neg bias PS go/no-go mains lockout.

On another forum, someone posted this about the Major: 

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!

It was thought by Ritchie200 (Jim) that the Major sounded best using the 12AU7 in the post concertina pre power tube position.
It was also noted that the UL output trannie is important for the tone.  Hammond and Heyboer are mentioned as good.  Ed Chambley prefers Dynaco replacement OT's for this design & contributed a lot of info along with Jim about this amp .

CHECK for ERRORS!   COMPARE all the schematics.  Post any concerns or question on the Tweaks forum.

NOTE:  the original amp has 250R screen resistors.  Jim (Ritchie200) actually owns a Marshall and recommends using 1k/10w screen resistors,  so that is where the 1k/10w value came from.

With respect, Tubenit

[tubenit]

This two tube version would be my preference.  CHECK for errors!

This idea has a switchable  OWM (one wire mod) and the PPIMV.

Should be noted that the 1k/10w screen values are recommended by Jim who owns a Major.

Pete (Dummyload) recommends the following PT & OT choices.  The Major Minor is the two KT88 version vs. four tubes.

Tubenit

[sluckey]

It was also noted that the UL output trannie is important for the tone.

Your schematic does not show a UL OT?

Also, the schematic I posted shows 39Ω resistors on each output tube cathode. I wonder if Jim would look at his and confirm?

[Ed_Chambley]

Maybe like this?

[tubenit]

OK, here is my proposal ........................    DRAFT IDEA.  I have NOT built this.

OWM & PPIMV & cathode biased with 375 v on the plates.  Based on my own Tweed BluezMeister B+ rail, I think I have made a reasonable guess on the dropping resistors for this idea.  Should get pretty close to the right Major preamp plate volts?

I am understanding this to be 30 watts based on page 3 of this data sheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/086/k/KT88.pdf

Edcor has a 275-0-275 PT with 325ma that would work just fine and is reasonably priced:
https://www.edcorusa.com/xpwr004

Edcor has a 30 watt OT that appears to be UL (?) that might be a good fit?:
https://www.edcorusa.com/cxpp30-ms-5k

With the 250uf (individual) cathode caps, I think it would emulate a reasonable fixed biased tone?

IF this works out to produce 30 watts of KT88 tone, then it may (at some level) honor the Major KT88 tone at a much more useable and realistic volume level.

With respect, Tubenit

NOTE:  NOT SURE about how the solid state rectification is drawn in this schematic!  Look at Pete's drawing. IF You have any questions , post on the forum.

[TIMBO]

NOTE:  Compare this to the Marshall Major

Hi guys, Being So far away from the rest of the WORLD back in the late 60s and early 70s meant the local (i'll include NZ) amp builders had to rely on local product to power their amps and this lead to some low powered out of the box designs to appease the masses.
And from the basic designed there was some major influences.
The HOLDEN WASP is a product of New Zealand and these guys hit the market big time with this amp and the bands loved them. They may have been the first of the MONSTERS, can't say I have seen any of these under 50w.
There claim to fame was Angus used them when ACDC first started.
We were hungry for big brand gear but not the cost so someone had to do something.
Ibanez flooded our shores with copies of great guitars and it now seems that our local amp builders were jumping on the band wagon.

This amp had a mod that removed the second channel inputs and rewired V1b in series to form a circuit similar to a OWM. I don't know when this was done.
From reports this amp is very sterile and clean to the max which I believe to be 100w.
After piecing the circuit together to what I thought would have been how it was originally, things started to look familiar. The preamp to the TS driver had two 470k mixing resistors and one had a bypass cap that to me looked very marshall.
Further, the TS driver and TS again very marshall. Then the PI and CATHODE DRIVER.......... WT#####
The component valves were different but not enough to make a difference.

Tubenit asked me to post a schematic.

We had to do it.   

EDIT:  I tried to redraw Timbo's schematic to a more concise version of current state with current mods.  It's the Timbo Holden Wasp & mods  Tubenit

[DummyLoad]

EDIT:

Pete has done 3 versions of this amp.  1)  original schematic   2)  100w version with fixed bias  &  3)  50w version with cathode biased.

THANKS to Pete for drawing these up and sharing them!!!



--pete


EDIT: fixed node A to V3 & will delete all other files posted in marshall major thread..

[jazbo8]

Missed it earlier, V3's supply should be connect to "B", not "A".

[DummyLoad]

major minor III (buck private) rev1.2


--pete

[amitay3333]

EDIT:

Pete has done 3 versions of this amp.  1)  original schematic   2)  100w version with fixed bias  &  3)  50w version with cathode biased.

THANKS to Pete for drawing these up and sharing them!!!



--pete


EDIT: fixed node A to V3 & will delete all other files posted in marshall major thread..

Hii, can someone send update PDF schematics (especially the 100W)?
has someone tried to build it?

[tubenit]

100w version

[amitay3333]

100w version

This schematic has 4 power tubes (meaning 200W), and pls explained me why ce1 being 47uf instead of 250uf and the power line- c6 and c7 supposed to be before 100k 2w to ground and then goes to V2 and V3?

[amitay3333]

100w version

This schematic has 4 power tubes (meaning 200W), and pls explained me why ce1 being 47uf instead of 250uf and the power line- c6 and c7 supposed to be before 100k 2w to ground and then goes to V2 and V3?

Anyone?

[Willabe]

Do a search for DummyLoad. Thread's he started. Look for Marshall Major started by DummyLoad.   

[amitay3333]

Do a search for DummyLoad. Thread's he started. Look for Marshall Major started by DummyLoad.

Can't find a thread he started, but I found a schem he posted(attached "Major Minor") and I'm still confused with C1 and the power line and C5 being the bright cap without the original 500pf cap?... have someone build it? I wanna add OWM & PPIMV and I saw another schematic(attached) can someone verified it?

[Willabe]

...and I'm still confused with C1 and the power line and C5 being the bright cap without the original 500pf cap?...

On the schematic tubenit posted?

And what are you you confused about? We don't know what your talking about, no explanation.

I wanna add OWM & PPIMV and I saw another schematic(attached) can someone verified it?

What is a OWM?

Use words, at least the 1st time, not letters, so we know what your talking about.

[amitay3333]

Why On the "Minor Major" schematic C1(connected to channel 1 cathode) being 47uf instead of 250uf?
Also, the original has two 500pf cap- one bridge between volume 1 and volume 2, and the other is the "bright cap"(some models come without it) connected between log 2 & 3 on volume 1, this schematic has the "bright cap" and not the other is it not going to affect the original tone?
Next thing is the power line- why between V2 plate resistors there is 25K resistor and 50uf cap? the order of components in the original schematic(attached) is difference.
There is additional 390k grid resistor connected to V2 pin 7 why?

OWM is "One Wire Mod", PPIMV is "Post Phase Inverter Master Volume"

[amitay3333]

Why On the "Minor Major" schematic C1(connected to channel 1 cathode) being 47uf instead of 250uf?
Also, the original has two 500pf cap- one bridge between volume 1 and volume 2, and the other is the "bright cap"(some models come without it) connected between log 2 & 3 on volume 1, this schematic has the "bright cap" and not the other is it not going to affect the original tone?
Next thing is the power line- why between V2 plate resistors there is 25K resistor and 50uf cap? the order of components in the original schematic(attached) is difference.
There is additional 390k grid resistor connected to V2 pin 7 why?

OWM is "One Wire Mod", PPIMV is "Post Phase Inverter Master Volume"

Any thoughts? I feel kind of stuck

[amitay3333]

What the plate voltage for the major version with two kt88 fixed bias? meaning what rating power transformer should I use?

[DummyLoad]

What the plate voltage for the major version with two kt88 fixed bias? meaning what rating power transformer should I use?

With a Hammond 378CX power transformer, about 540VDC. Use the Hammond 1650RA for the output transformer.


--Pete

[amitay3333]

What the plate voltage for the major version with two kt88 fixed bias? meaning what rating power transformer should I use?

With a Hammond 378CX power transformer, about 540VDC. Use the Hammond 1650RA for the output transformer.


--Pete

How much lower can I go without any mode for the two KT88 fix bias? can I go 75W for instance?  does 360V transformer can do the job?(not CT)