marshall modding experts assemble...

ChrisCox1994

I've got an idea in my head of converting an old (early 70s?) 100w super PA into a dual master volumed beast of a marshall.

Volumes 1 and 2 as pre amps and volumes 3 and 4 as master volumes respectively.

My questions are:

Has this been done?

Are there any schematics for the mods floating about?

Would it be a relatively easy job for a competent tech?

Monstronaut

It will be possible but you'd be ruining a pretty collectable amp. Why not sell it and buy a Friedman or whichever modded Marshall floats your boat?

Ossyrocks

Agree with above. It’s nice amp already and pretty collectible.

You can make small reversible mods to separate channels to make one Super Lead and one Super Bass. I did this to one and used it for a few years. Great amps.

Rob

ICBM

You could do it fairly easily, yes - a simple relay switching circuit to select the different controls would work. But as already said it’s probably not advisable unless you’re starting with one that’s already fairly knackered from a value point of view. Revoicing the channels to Super Lead and Super Bass seems to be an accepted mod that doesn’t affect the value - it’s just changing a few cap and resistor values - but anything more extensive will.

ChrisCox1994

hmm, it is a pretty beat up example that had been in storage from the 80s (it was actually used as a pa back in the day) then checked over by a marshall expert player locally and seen to be working. 

Cosmetically its pretty bad but it works on all channels, one speaker output makes a popping sound but the other is fine. 

I didnt think it had amazing value - compared to a superlead 100 say - its probably not even work as much as a friedman, so why not mod this one to be more flexible and its the "real deal" vintage marshall. (i'm not really after the high gain thing anyway) 

I'll try and get some photos soon and see what you all think - at the moment its just not getting used at all, so I'd rather mod it and use it than leave it to not be played...

Modulus_Amps

Generally I am against modding 50 year old amps like this, but if you must then yes it can be done, what is a modded marshal though, you need to know what you want out of it in the end.

I can do this sort of thing, Dan Gower has a range of mods you can check out too.

Ossyrocks

Modulus_Amps said:

Generally I am against modding 50 year old amps like this, but if you must then yes it can be done, what is a modded marshal though, you need to know what you want out of it in the end.

I can do this sort of thing, Dan Gower has a range of mods you can check out too.

I sold an absolutely mint ‘79 Super Lead on this forum, and I mean mint. The buyer had me ship it to Dan Gower. I was gutted to be honest, but he’d already paid, so what could I do?

Modulus_Amps

Ossyrocks said:

Modulus_Amps said:

Generally I am against modding 50 year old amps like this, but if you must then yes it can be done, what is a modded marshal though, you need to know what you want out of it in the end.

I can do this sort of thing, Dan Gower has a range of mods you can check out too.

I sold an absolutely mint ‘79 Super Lead on this forum, and I mean mint. The buyer had me ship it to Dan Gower. I was gutted to be honest, but he’d already paid, so what could I do?

Ooff, I don't get it, you can buy really good parts for a 100w amp for £600 - £700 without a cab and any builder should be able to make it a cracking amp, or you can buy a cheap 100w amp (DSL etc) and gut and mod that

ChrisCox1994

Is it better to mod it or leave it to sit in my dads living room behind a sofa?

If someone wants to use a 4 channel 100w marshall head in 2019 pm me and we'll see if we can agree on a price 

I guess I like the idea of "resto mods" when it comes to cars - so the same thinking applied to this idea for the amp, but I see some people think its sacrilege... 

clarkefan

It's a bloody weird thing agreed.

Even doing *necessary* work on old Marshalls in the past (filter caps on motorboating 69 PA head, blown mains transformer on a 71 SL head spring to mind) I couldn't shake the feeling I was doing something wrong to history with the soldering iron.

It's your amp mate.

Ossyrocks

Please could you try to post pics? Depending on condition it could be quite valuable. Someone would love this amp, and you might be able to buy something more suitable with the cash.

ICBM

Of course it’s your amp to do what you want with, but I just don’t really see the point of hacking it. You don’t have to mod it into a channel switching amp to make it useful - even stock, it will sound wonderful with a boost pedal and an attenuator, and both of those might well cost less than having it modded. Or simply use it as a clean platform for an external preamp - they also sound fantastic for that. A simple Super Lead/Super Bass mod and/or a post-phase-inverter MV will also make it more versatile without compromising the value.

p90fool

One of the best clean sounds I ever got from a Marshall was from one of these, it was really special. It was also fantastic, rich and detailed with drive pedals. 

Seems a shame to mess with that tbh. I dare say nobody would molest them if it had been marketed as a guitar head instead of a PA head, it would be regarded as an all-time classic.

Just write "guitar" on the front with chalk, plug it in and enjoy it.  

ChrisCox1994

I think some clarification is in order...

I assumed its a pretty non invasive mod (and one thats done regularly) to do PPIMVs on old marshalls. 

My idea was just doing this twice then A/B/Y manually switching the channels, im not talking about relays and digital switching blah blah, it'd be just like having two mastervolumed 100w marshalls in one box. 

Plenty of people have old 100ws and 50ws with MVs fitted and they're by all account easily reversible, is there a reason it would be hard to implement twice in the same amp and still use two of the channels (switching with an ABY?)

ICBM

ChrisCox1994 said:

I think some clarification is in order...

I assumed its a pretty non invasive mod (and one thats done regularly) to do PPIMVs on old marshalls. 

My idea was just doing this twice then A/B/Y manually switching the channels, im not talking about relays and digital switching blah blah, it'd be just like having two mastervolumed 100w marshalls in one box. 

Plenty of people have old 100ws and 50ws with MVs fitted and they're by all account easily reversible, is there a reason it would be hard to implement twice in the same amp and still use two of the channels (switching with an ABY?)

There aren't enough preamp valves to implement two PPIMV circuits, you would need six - plus dual-gang pots to make two separate tone stacks. Even to do two standard MV circuits with a common tone stack and phase inverter would need five - two each for the preamps plus one PI. There are only four...

The only way to get what you want without hacking the chassis even more for extra valve sockets is with relay switching.

ChrisCox1994

ICBM said:

ChrisCox1994 said:

I think some clarification is in order...

I assumed its a pretty non invasive mod (and one thats done regularly) to do PPIMVs on old marshalls. 

My idea was just doing this twice then A/B/Y manually switching the channels, im not talking about relays and digital switching blah blah, it'd be just like having two mastervolumed 100w marshalls in one box. 

Plenty of people have old 100ws and 50ws with MVs fitted and they're by all account easily reversible, is there a reason it would be hard to implement twice in the same amp and still use two of the channels (switching with an ABY?)

There aren't enough preamp valves to implement two PPIMV circuits, you would need six - plus dual-gang pots to make two separate tone stacks. Even to do two standard MV circuits with a common tone stack and phase inverter would need five - two each for the preamps plus one PI. There are only four...

The only way to get what you want without hacking the chassis even more for extra valve sockets is with relay switching.

ok cool, thats what I wanted to know - thanks 

normula1

Speaking as someone who converted a '73 50 watt head into a channel switching fire-breathing rock monster back in the late 80's / early 90's because it was just an old second hand amp (and I couldn't afford anything else), if you do decide to get it modded, please avoid drilling new holes. I put mine back to stock 18 months ago and trust me rubber bungs ruin the look