Marshall 100w jmp super p.a. 1969 4 inputs

fastonebaz

Ok hope this works.  Loads of pics.  1st time I've opened her up. Yes i still have the original tubes that were taken out 25 years ago (somewhere). At that time the main power in socket was converted to a modern kettle lead. Other than that as far as i know it's original.  But you guys are the experts.... what do you reckon?  

fastonebaz

Pics here

fastonebaz

Marshall JMP super p.a. 100w https://imgur.com/gallery/hXDb0

lukedlb

It looks lovely. I've heard 2 plexi PAs, different in sound but my what possibilities they both possessed. A super lead, a super bass and a fantastic clean, blended together even better, and an incredible saturation at high volume. And we are talking loud. 

jkirk170493

fastonebaz said:

jkirk170493 said:

They're great. Americans go crazy for them! We've had a couple of them in the past and never struggled to sell them. In fact we were tempted to keep one as 'our' amplifier! You've got a beauty - don't let it go cheap if you do decide to sell it!

What do you think it's value is for an excellent condition one?   I will take some pics tmrw i think. 

Your pics look great! If I'm not mistaken, it looks like the dates on the caps are C9 which means 3rd quarter of 69. It could be 69 or 70 from the serial number. What date does the label say on the chassis?

As for as what it's worth - it's worth as much as someone is wanting to pay. But, for reference, here are a few links to help you:

One sold through here in 2015 for around £1150 (which is a very good price in my eyes!) - 

http://www.thefretboard.co.uk/discussion/46142/fs-marshall-super-pa-1969-vintage-amplifier-100w-1150ono

Here's a few older ones, hence more expensive than yours:

https://reverb.com/uk/item/6241-marshall-super-p-a-1967-clean

https://reverb.com/uk/item/1354000-marshall-jtm-100-super-pa-amplifier-1967-black

https://reverb.com/item/1405032-marshall-super-pa-1966-black

Finally, I've got an early one up for sale that has the white back panel which I've stuck a high price on as I can't bear to part with it (sounds too good and looks too good in the showroom!):

https://reverb.com/item/4577105-vintage-1966-marshall-jtm-50-super-pa-mk3-iii-valve-amplifier-head-serviced

Hope this helps?

DJH83004

IMHO it is the perfect condition for a collector just about as original as they get. Slight shame about the IEC socket fitment, as you can now get TAD replacements that cover the whole cut-out and don't need the tape to make up the gap. For a gigging amp, certainly bias caps and cathode bypass caps would need changing, and maybe main filter caps at a push, and of course valve test / replacement and bias. But a lovely bit of kit, great to see original amps like this, I'm sure IC would agree. 

ICBM

DJH83004 said:

IMHO it is the perfect condition for a collector just about as original as they get. Slight shame about the IEC socket fitment, as you can now get TAD replacements that cover the whole cut-out and don't need the tape to make up the gap. For a gigging amp, certainly bias caps and cathode bypass caps would need changing, and maybe main filter caps at a push, and of course valve test / replacement and bias. But a lovely bit of kit, great to see original amps like this, I'm sure IC would agree. 

Yes, absolutely - and I agree, for a collector/home player I probably wouldn't re-cap even an amp this old unless there was a clear sign of a problem. For a gigging amp I would - but I wouldn't gig a vintage amp this pristine anyway. As far as I can see it's 100% original apart from the power socket.

The IEC socket conversion is just what it is - when it was done, the TAD replacement wasn't available, and the new socket is still safer than the original. The only thing I don't really like is that the mains voltage selector appears to have been left operational, this should have been hardwired at the same time.

The replaced power valves are Zaerex labelled RFT, AKA Siemens, which are *very* good valves - they would have been NOS even when the work was done, they're from the early-mid 80s at the latest. The Brimar preamp valves may be original, Marshall used these as well as Mullards, and later RFT preamps too. If not then they were also old when fitted.

Be sure to check that the bias is OK, since failing bias filter caps are a common problem - actually more than the main filters - and if they die it will cook those nice EL34s. The usual symptom is that the bias trimmer has to be turned to the max to get just about enough bias voltage, which that does look like it is.

fastonebaz

Thanks all.  The label inside it says it was tested and approved 11th feb 1970.  Previously I've had email confirmation frying Marshall that the serial number is from 1969 so thay seems to tie in.  I'm curious what the original tubes are I've got stashed in the shed somewhere.   But,  i honestly don't get what the fuss is about with these super pa amps though.  They only sound clean.  No drive/ gain/ break up at all as far as i can tell  from the few times I've tried it.  Is it meant to have any? 

What's involved in that mod to have 2 channels as super lead and 2 as super bass? 

ICBM

fastonebaz said:

But,  i honestly don't get what the fuss is about with these super pa amps though.  They only sound clean.  No drive/ gain/ break up at all as far as i can tell  from the few times I've tried it.  Is it meant to have any?

No. But then again nor was a Super Lead…

They are not modern Master Volume amps. To make then distort, you turn them up loud. But don't, unless you've connected both speaker cabs - and probably still don't if you value your hearing…

The reason they are so valued is because you can turn them up like that in a studio, or if you use an attenuator to control the volume - and for that wonderful clean sound, which takes pedals so well.

fastonebaz said:

What's involved in that mod to have 2 channels as super lead and 2 as super bass? 

Adding an extra cathode cap and resistor, changing the coupling cap and adding two bright caps (on channel 1), and adding one bright cap (on channel 3).

None of this will make it distort at low volume, it just changes the voicing.

lukedlb

A friend of mine has near a dozen stacks from 67 until 72, bass tremolo lead and pa. They all sound different from one another even the two pa plexi from the same year. 
Jacking the two inputs together will provide the best of both worlds with the aid of a simple pedal jack cable. Blend them well and punch the volume on a full stack will provide some excellent drive and saturation. But then you could just have an amp with a remarkably clean high volume. 
As for checking the amp out I would trust no one unless you the forum can back them up or you have reliable feedback. I am now on my 4th amp pedal guy. The last three were all recommended and seemed reliable but all 3 let me and others down. The 4th is probably the last local one we have here in Bologna and my friends and I are slowly testing him with some small repairs. So far so good and more importantly quick too. 
Ideally you're after someone who can confirm that the amp is fine and give you a diagnostic report for your cash.