Also have a Super PA amp and looking for some info

[KevNukes]

Hi esteemed Marshall experts!
I’ve found my way here because I have to find a new home for my Marshall Super PA amp. We are downsizing from a 3 bed house to a 1 bed flat with very little storage, so my historic equipment has to go, sadly! Plus, I can’t really afford to get the amp serviced, so I’d rather it went to an enthusiast who can get it back into working order and enjoy it.
I bought it in the late 70s from the guitarist in a band called More. My Dad was an electrical engineer and made a couple of mods. Looking at the circuit, it doesn’t seem like it has been too intrusive. I’m not sure if the large black knob between the inputs was standard (I’ve not come across any photos that have this) but it was already there and was originally an input selector, I believe. My Dad converted it to a master volume. He also converted a pair of the inputs to be an fx loop.
Sadly, the amp hasn’t worked for some time. I have no idea what is wrong. I always assumed a valve had blown, but I can’t be sure. I did have some spare valves but have not come across them, unfortunately.
I’d be very interested to learn more about my amp and also how I could go about selling it to someone who would appreciate it. Interesting that this very day, another Super PA was posted here! I wonder how many are still around!?
Some photos here. I can take more, if necessary, just ask.




Thanks for any help you can give.
Kev

 

[TAZIN]

Nice amp!...And it has the RS potted military PT!.. @Ned B . She's had some changes but it's in good shape for an amp from around April 1966. It looks like someone did a little re-voicing for the individual channels. Some of the changes I noticed are:
The cathode cap for V1 has been replaced.

Someone added a bypass cap (can't make out the value) for the 270K summing resistors for channels 1 & 2.
The preamp coupling capacitors for channels 3 & 4 have been changed to what looks like 0.1uF instead of the usual 0.022uF.

The cathode follower 100K resistor has been replaced.

The preamp filter cap has been replaced with a dual section cap. Original would have been a 16uF/450Vdc. Also someone added an addition 10K/1w B+ voltage dropping resistor at this filter cap.

The bias circuit has been updated with a slider trim pot and at least one bias cap has been changed at one point.
An additional 32uF/450Vdc filter cap was add.

Looks like the diodes & 0.05uF/1000Vdc cap for the rectifier circuit changed at some point. They look like IR diodes but typically around this time frame they were using metal cased Mullards.

The On/Off switch has been replaced.

Not sure why the OT has R/S 207-330 written on it...To me it looks like a Drake 1202-84 which would be period correct. Looks like someone moved the Yellow 8-ohm tap wire from the Selector to the speaker jacks....

The choke looks like a replacement.

 

[AndyD]

At least one of the output valves has blown! Nice bit of history.

 

[Matthews Guitars]

What has happened to the back panel printing? It looks like the ink has decided to liquefy and migrate away from its original location.

Maybe someone tried to clean it with a solvent that wasn't ink safe?

I doubt I can afford this amp but I'd surely be interested at the right price.

 

[chocol8]

Where are you located? That is a project I would be interested in.

 

[StingRay85]

Damn, now THAT's a PT. It seems a bit rough but there's some gold below the dust and dirt!

Where are you located? It needs proper restoration and servicing. In any case worth a few K

 

[StingRay85]

The Evolution of the 100W Circuit: From JTMs to JMP Superleads

From Fil 'SoloDallas', just an introductory word for our friend Roe. Roe has been on the hunt for AC/DC's tone at least since I have been; that means, years a

solodallas.com

Yours has S/N 6753, while the Super PA amp in this link above is S/N 6784 (in a bit better shape though)

 

[neikeel]

I agree with Tazin
Broadly all there, nothing particularly missing. There are bypass caps on a couple of the preamp mixers (like the lead/bass amps)
Interesting to see the big 0.1uF couplers on channels 1 and 2.
It's had a life (battered front panel and extra hole)
Likely early 66 (the PAs ran both 1203-43 and the RS synchronously for a short while)
Well worth some time and effort.
Where are you based|?

Also interesting to see a couple of my amps on the Solodallas site attributed to Amparhcives!

 

[Whatwhatringrang]

Holy crap ! Love that power transformer .

 

[Matthews Guitars]

We've had two JTM100s in the spotlight here this week. Would someone be so kind as to give me some dimensional information regarding them so I can design the front and back panels for them? Length of the chassis, length of the panel, etc. I am presuming that all the jacks are spaced 1.5 inches apart, as are the controls. Stretching a Superlead front panel and adding controls and another quad of jacks should be most of the work to be done.

 

[playloud]

Wow, what an incredible (and rare) amp! That PT is truly formidable. I hope you find a good home for it - maybe even with someone here?

Also interesting to see a couple of my amps on the Solodallas site attributed to Amparhcives!

Did they make it into the version in the Doyle book too?

 

[Whatwhatringrang]

Yeah that amp is really a piece of Marshall History! Strange that it has el34s in it. By any chance is it in the U.S.A? Probably U.K. judging from the voltage selector.

I have never heard that big RS power transformer version in person or even on the internet . If the transformers work it would be amazing to hear it when sorted out.

If you are in the U.S. I can mail you a quad of Chinese kt66 tad but I would not recommend turning it on anyhow straight away. Still needs a check up.

If who ever gets it on here I have some good quads of gecs I would let go if you don’t have a nice quad of gec for restoring this. The guys on here would know but these big rs transformer don’t throw the really high plate voltages like the slightly later 3 stack ? Choke does look changed but I not 100%. Still amazing . Send me a price lol serious. I vote Neikeel on getting this to him.

The guys around here will be great a bunch to give a new home. Restore it and really appreciate it. I think only the dual output transformer version would be more rare. One will probably pop up soon here .Season of the pa.

Wow some really cool stuff pops up here The only bad thing about these early pa are how heavy they are. I can imagine how heavy that big rs pt is. The regular guitar version always feel a
noticeably easier to move.

 

[KevNukes]

Thank you all for your feedback. It’s fascinating to find out the details and exciting to hear it is a rare example. I had a feeling!
I’m in North London (Enfield). Open to offers. I have no idea of a value, but there’s a working one on eBay for £2195, although it seems like that one is from 69. I’d love to see it go to someone who could restore it properly. I’m not after silly money, but I could certainly do with getting a fair price, if it’s worth something, because I’m super skint at the moment.
I don’t know what happened to the ‘Super PA’ sticker on the back. I had the amp in the loft, so it might have been a bit damp. I don’t think I used a cleaner on it. I was surprised to find it almost invisible, when I got the amp down. I never had the original Marshall Logo on the front, which I was always disappointed about.
Here’s a photo showing me using the Marshall in 1979! Wow, 43 years ago! I had some sort of weird setup, with the Sound City going through the Marshall. Can’t quite remember why.

 

[neikeel]

I'm tempted but I already have an amp with that PT and have a skiing holiday to pay for!

 

[Matthews Guitars]

Here's what I'd recommend: Let Neil (Neikeel) work on it and bring it back up to its full glory. Then it can be sold for a very good price indeed. Pay Neil for his services out of the money it will bring. Neil is certainly among the most qualified people on earth to restore that amp and make it right as it can be.

I personally would be interested in it but I know I can't justify paying what it will likely bring even in its current state. And then there's the issue of shipping internationally...

 

[StingRay85]

Sweet. Its difficult to value in non-working condition. It will always be at least the value of both transformers.

What band did you play in?

 

[AndyD]

I'm tempted but I already have an amp with that PT and have a skiing holiday to pay for!

Go for it!

 

[chocol8]

It will always be at least the value of both transformers.

Assuming they both work. It has a value in its current condition where the buyer accepts the risk. It has a higher value once repaired or at least tested and the seller has taken on the risk and expense. Finally there is an even higher value if it is well restored to near original condition at even higher cost to the seller.

I am an interested buyer in the first case, and maybe the second. I would love to fix that thing up and then play it so loud I can't hear my wife screaming at me to turn it down! That's amp heaven!

 

[Seanxk]

Very nice amp Kev, hope it finds a good home, I'm very interested, but I too have a Skiing holiday to pay for.
Just to clarify the '' blown valve'' ( the white one ) is not blown, at some point it has been hit and cracked allowing in air which has oxidized the internal coatings, it's dead but not blown. I still wouldn't power it up if you find a replacement though, a transformer test is needed first.

 

[neikeel]

I’m happy to work on it for free if Kev pays for parts and gets it to me.