THE OFFICIAL Marshall "Lead & Bass" thread

[Guest]

Every so often I see posts on various boards asking about the Marshall "Lead And Bass" amp/circuit. Unfortunately, not many of these amps were made and the posts I've seen contain little information beyond what is found in Doyle's "History Of Marshall" book. So here might be a good place to start a thread I pray might grow more in depth on the subject.

I picked up a circa 1975/76 2187 50-watt 4-input combo (2-12" combo version of the 1987 circuit head). These combos are mounted in the cabinet like a VOX combo and REALLY suffer from the retained heat. This was causing the Marshall ST1 (iss.202) printed circuit board to lift traces and exhibit some rather strange sonic symptoms at operating temperature and volume -- the vibrations just caused several bizarre things to happen. Hard to diagnose until the board was actually removed.

Seems like my best choice is to replace this damaged board with one of George's boards and opt to change the circuit to the 2100 Lead And Bass circuit while I'm at it.

As I understand it, the 50-watt 2100 Lead & Bass combo is the same as the
1964 Lead & Bass head, so I found a schematic for the Marshall 1964 and sent it to George. He's working on that replacement board now and I'll keep up on this project and results here.

Of course, I'd really appreciate any input on my thinking here as I could be COMPLETELY WRONG about the circuit being exactly the same as the 1964 head circuit. But on the bright side, it's a Marshall circuit and all the differences seem to be so minimal that a second visit to modify the new MetroAmp circuit board should be a breeze (unlike that old pig Marshall pc board!). Anybody have an schematic from Marshall specifically for the 2100 combo model? I'd love to hear about it!

Perhaps George might speak to the circuit differences either coming from the 1986 Bass circuit and from the 1987 Lead circuit -- or BOTH. Cool!

Also -- If you see and posts on other boards concerning these "Lead & Bass" models, please direct the posted here or add a heads-up to this post.

Thanks
-- Sonar

[Sonarguitar]

Okay.....time for an update.

The ptp replacement board, wire and supplies arrived from MetroAmp in perfect shape. Board was pre-stuffed and looks GREAT.

Damaged original printed circuit board (circa 1977) was removed last night. All original components left on original board for comparison. All original wires left intact and connected to the original board.

I'm about to install the MetroAmp board and there is one consideration specifically for swaps of this era Marshall board and model I should mention.

This is one of the Marshall models without a power or voltage selector on the back panel of the chassis. The power tranny voltage selection is made with a jumper between lugs on the circuit board. WELL, I forgot to ask for the row of seven (7) lugs to be placed on the edge of the replacement board for this purpose. Not a huge deal, but it would have been nice and neat to have thought of this when ordering. (I'm mentioning this in the interest of the "perfect" project situation for the next person trying something like this).

I'll just terminate and wrap the additional power transformer voltage wires (for 130v, 220v, 240v, etc.).

Okay.....now I've put the new board in place and it's a perfect fit for the mounting holes in the old board. It looks FANTASTIC in place.

Tomorrow comes the new wiring!

[VelvetGeorge]

Actually, I'll take the blame for not suggesting the extra lugs.
It should have occured to me.

Anyway, let us know how the wiring goes, and how it sounds when you fire it up!

George

[Country Boy Shane]

Also watch out for those bitch-ass filter caps. My dad says that he's been knocked on his rear a couple of times repairing my grandma's TV!! Blue arcs anyone.

[clay_finley]

Hey, can one of you guys post the Lead & Bass schematic?

[Sonarguitar]

Hey, can one of you guys post the Lead & Bass schematic?

Well, this doesn't bode well for my 'lil project as I got the schematic I began basing my MetroAmp board on from a link from Clay's wonderful Marshall Amp Page

I'm using the Marshall 1964 Lead and Bass schematic found on the Marstran schematics page http://marstran.com/1964.gif

It is marked Lead and Bass on the 1964 schematic itself, but that's all I know. The 1964 schematic shown on the Martran schematic seemingly only differs from the 1986 Bass schematic by just one component value......in the tone stack section of the 1964 it shows a 500pf cap with the slope resistor vs. a 250pf cap in the 1986. Both the 1986 and 1964 show a 56k slope resistor.

First, I should back up and say that the reason I'm seeking to tweak my 2187 Lead combo into a 2100 Lead And Bass combo is because a close friend had a rather beat 2100 combo that was the best sounding amp I've ever heard him play. He sold it and later regretted it. I thought I'd try this project to learn more about that particular amp.

So, admittedly, I'm employing guess work here, but one other clue came up while looking at the output transformer on this 2187 combo. Okay, it's less a "clue" and more of a BIG STICKER.

Looks like this:

The sticker there gives tube information and shows the 50-watt models as follows:
1986 - 2100 *Bass head / Lead & Bass combo
1987 - 2187 *Lead head / Lead combo
2204 - 2104 *MV Lead head / MV Lead combo

So, if these correspond as "head - combo", then it seems to make sense business-wise that Marshall might have simply put a 1986 Bass chassis into a 2-12" combo form and marketed it............but there's a problem for them.......

What would they CALL it?

I mean, who wants a 2-12" 50-watt open-back bass combo?

So, I could see the marketing approach of calling it a LEAD AND BASS. That just might sell!

And perhaps they did change the tone stack to a 500pf cap (instead of the 1986 Bass model's 250pf cap) with a 56k slope resistor for the 2100 combo version. I suspect that might be about all the difference between the 1986 & 2100 chassis.

As usual, I could be COMPLETELY WRONG, but any other info, views, ideas, and corrections are certainly welcome.

[VelvetGeorge]

Hey Sonarguitar, have you fired it up yet?

I'm anxious to hear your results.

George

[Sonarguitar]

Hey Sonarguitar, have you fired it up yet?

I'm anxious to hear your results.

George

I got it wired up and back in the cab. For some reason the neon light in the rocker power switch chose now to burn out. Replacement on order.

*NOTE: Parts is Parts (Sprung) has this switch with 4 connections on the back instead of the original 5, BUT MojoTone has SIX (6) connector models. Approx. $10 at both sources.

The re-wiring gave me a chance to check EVERYTHING. Went quite well. This project has given me a great feeling of dependability about this amplifier now knowing almost every connection has been checked and re-checked.

OKAY......I fired it up with the tubes that came with it (questionable EH 6CA7s). New tubes are also on the way from Lord Valve.

Through the pair of Celestion 65s in the cab it sounds GREAT! Quite note responsive and dimensional. That's the biggest change......DIMENSION!

I thought it might be too dark to start (as it basically is a bass amp design) but this hasn't been the case. It's very '60s & '70s rawk and just what I sought. I'm not looking for gain because I have VHT amps for that.....also.....I'm OLD! Looking for a classic rock sound in a reasonable package.

So, the voicing is great for single coils....might need a bit of sweetening for regular Humbucker use, but that ain't me. The best part is that slight voicing modifications and experiments are now easily done......also no concerns of effecting the "collector value", but I still feel I'm getting the best of classic Marshall tones within reason and budget.

Later, I might look into Mercury Magnetics or Obsolete output transformers, but even with that upgrade I'd have a PTP Marshall carefully wired in a classic Marshall circuit coming in at a total cost of approximately $1,000 total. I couldn't lose a penny on this project if I tried!

BOTTOM LINE: Cost was right, quality is first-class and all told, the project appears a roaring success! An absolute keeper!

[Guest]

Hey, can one of you guys post the Lead & Bass schematic?

Well, this doesn't bode well for my 'lil project as I got the schematic I began basing my MetroAmp board on from a link from Clay's wonderful Marshall Amp Page

I'm using the Marshall 1964 Lead and Bass schematic found on the Marstran schematics page http://marstran.com/1964.gif

Thanks for the schematic! I think Brian had added some new ones up there and I hadn't seen that one (but was looking for it).

The 500pf cap looks like it adds a bit of mids.

[Country Boy Shane]

DO NOT MENTION PARTS IS PARTS I AM SO PISSED AT THEM! The very first time I ordered from them i specifically mentioned a gold pickup cover for the neck and one for the bridge. I finally get the part over to my guitar tech who was doing some maintenance and he says that the bridge cover was actually a neck!! WTF!!!! They sent me two neck pickup covers... what trash. They said it wouldn't happen again and it was their mistake, but here is the real doozie. My volume pot in my Les Paul started to crap out and wouldn't hush its crackling up. So i ordered a LONG SHAFT 300Kohm pot from them and waited 2 weeks for it. It finally comes in the mail and i'm excited as ever to replace it. I open the package and it's a short shaft!!!!! Talk about frustration. That's two screw-ups in a row from those asses. I'm not ordering from them again......

[clay_finley]

Hey George, I re-registered as clay_finley and it marked my reply as guest. This is a test.

Hey, it worked! I must have re-registered and then forgot to login before posting above.

Doh!

[Country Boy Shane]

posting woes.

[dewey342]

Hi everyone, I see this thread hasn't been used in quite a while but does anyone
have any pictures of an early 2100 combo?
Maybe even a 2187 combo while your at it. What I'm interested in is the grill cloth.


Thanks!
Dewayne

[lifer]

always wanted one of these---------

[dewey342]

Yea, I have a 1987 chassis I built and am having a combo cabinet built
for it. I have seen what I think to be a 2100 with large checkered grill
cloth but I'm not for sure that it's a 2100. Also I know the 2187's I have
seen used this cloth also.
I'm wondering if any of the earlier models ever used a basket weave or cane
style cloth.