Super PA Thoughts...

[8bit Barry]

Hi there everyone

I would like to be able to post pics but as this is my first post it wont let me - I need three posts before I can apparently.

I have a Super PA that has sat around doing not very much over the last 15 years (bought for £200). I also have a 4x12 cab that I bought separately and kept after selling a four input 1979 Marshall 100w non master volume lead head that came with it as part of the sale. That was no for me (so ear-splitting and screechy). I realised the cab was full of pre-rola Celestions and sold the head.

Dating the two I believe the Super PA is 1969-70 and the cab is an angled #1935 from 1971... I have put some pictures in there for you to have a look at.

I have a Weber Mass Lite 100w set to LOW (max attenuation) and then controls dimed half way - its so loud that its unusable without it. It's not a gigging amp, its for enjoyment at home. I am not in a band.

I want to get the cab weave sorted out as its terrible, a cheap job of nasty black cloth done before I bought it.

Q - What weave is the correct weave?

It's got a HUGE DEEP SOUND, but I am not a collector / purist, so I want to get it under control and get more enjoyment from it. I am thinking getting a good tech to reduce the power. I have another two master-volume amps, a 2204 and a rare 2144 combo with 6db boost, but never massively liked the tone of them. They sound like 80's metal (I prefer classic rock sounds)

Q. What mods would you do to this amp? I am not sure what to do.

 

[Matthews Guitars]

If you pull two power tubes (the outer two) and set the impedance selector to the next HIGHER setting, you'll be at half power and at a safe load.

But, half power is only 3 dB quieter, so it'll still be very loud. There's not a lot that can be done to reduce the amp's output to the point where it's all THAT much quieter when cranked. And you'll lose the grinding distortion of the output transformer in magnetic saturation if you do that anyway.

You're really not going to be able to reduce the power by any reasonable mods. If the amp is just too loud for you then it may simply be the wrong amp for you.

As for grill cloth, pick the pattern you want. Various types of basketweave and checkerboard patterns from that era can still be found, and if you prefer pinstripe, there's a Marshall reissue type that I went with because it looks good and its price is reasonable, but for a full-on restoration of a vintage cabinet that had bluesbreaker/pinstripe cloth on it, you could go with the E.C. Collins reissue Bluesbreaker cloth, which is as authentic as you can get today, but at a price that will choke a goat. Something around 350 bucks for a piece big enough to re-grill one 4x12.

Sources: E. C. Collins, Mojotone, Amplified Parts, Speakerbuildersupply, a few others if you search for them.

 

[boola1]

Q. What mods would you do to this amp? I am not sure what to do.

Hi,

I have exactly the same head, 69/70 100W PA.

It doesn't have enough distortion for my tastes and I'm more partial to 50 watters anyway. It did do a good job as a power amp for my Mesa Quad preamp - I guess that's kinda what it was designed for

Personally, I wouldn't bother pulling 2 tubes, it doesn't greatly reduce volume and for me it reduces the sound quality too much.

I had earmarked my amp for sending to Dan Gower for the Jose mod but haven't heard from him for 6 months so I wonder if he's snowed under.

It's a great modding platform because it has the extra channel with it's preamp tube, volume controls and inputs - no need to drill holes. The world is your oyster.

It sounds like our tastes are different so the only advice I would give is to install a master volume, see how you like it and go from there.

If you like the sound of a 100watter cranked, I'm afraid it's quite hard to replicate that at bedroom levels. Also, you are right on the limits of that Weber attenuator - your amp is capable of putting out considerably more than 100w. Be careful.

 

[Matthews Guitars]

Marshall lists a "100 watt" amp as putting out 170 watts RMS at 10 percent distortion. So, yeah, they're really a lot more powerful than 100 watts. They're nearly double their listed wattage that at full tilt.

 

[neikeel]

The correct and most robust cloth for the cab is this stuff:
https://www.ebay.co.uk/itm/Marshall-SALT-AND-PEPPER-Speaker-Grill-Cloth-Basketweave-/112660311326
The best mod for these (DON'T DRILL ANY HOLES) is to adopt channels 1 and 2 as a 2203. The volume pot for channel 1 becomes the pre-pi master volume (1 Meg audio pot between the treble pot wiper and the PI input).
Next you take a 500pF mica cap and place it in parallel with channel 1 mixer (470k resistor) and ground the other 470k. Then you cascade V2 b into V2a after splitting the cathode to a 0.68uF/2k7 and an 8k2 combination. Use a 470k treble peaker between the stages but my tip is to use a 2200pF (or 1800pF) bypass cap in parallel with this.
Channel 2 volume pot will become the 'gain' pot. Move your NFB resistor (that will be 27k) from the 16ohm tap on the selector to the 8ohm tap.

Next, to minmise bleed between channels I suggest desoldering the green grid wire from channels 3 and 4 and putting a switch in line so that you can connect channels 3 and 4 if you want a flat EQ input for some reason. You can use a SPDT switch in one of the now unused channel 2 jack holes. Save all the parts and wires, including jacks.

That is the simplest best way to get a PA amp to rock at sensible volumes. There are loads of others that work but need more work and explanation.

 

[troyvod]

i had a 1969 Super Pa, ended up selling it as it didn't get as much use as it should have. Great pedal platform, but a little too clean for my taste. i had a hotplate, which tamed it enough at 12 - 16 db cut

 

[8bit Barry]

If you pull two power tubes (the outer two) and set the impedance selector to the next HIGHER setting, you'll be at half power and at a safe load.

But, half power is only 3 dB quieter, so it'll still be very loud. There's not a lot that can be done to reduce the amp's output to the point where it's all THAT much quieter when cranked. And you'll lose the grinding distortion of the output transformer in magnetic saturation if you do that anyway.

You're really not going to be able to reduce the power by any reasonable mods. If the amp is just too loud for you then it may simply be the wrong amp for you.

As for grill cloth, pick the pattern you want. Various types of basketweave and checkerboard patterns from that era can still be found, and if you prefer pinstripe, there's a Marshall reissue type that I went with because it looks good and its price is reasonable, but for a full-on restoration of a vintage cabinet that had bluesbreaker/pinstripe cloth on it, you could go with the E.C. Collins reissue Bluesbreaker cloth, which is as authentic as you can get today, but at a price that will choke a goat. Something around 350 bucks for a piece big enough to re-grill one 4x12.

Sources: E. C. Collins, Mojotone, Amplified Parts, Speakerbuildersupply, a few others if you search for them.

Thank you for your detailed response. I really appreciate it. I had it in my head that pulling the tubes would make a significant difference, but there are others who reflect your thoughts too.

Thanks for the info on the grill cloth too - I should of mentioned I am in the UK, but the sources will no doubt ship to across the pond. It depends on whether it is economical but there are bound to be suppliers here too. I'm on a mission now.

 

[8bit Barry]

Hi,

I have exactly the same head, 69/70 100W PA.

It doesn't have enough distortion for my tastes and I'm more partial to 50 watters anyway. It did do a good job as a power amp for my Mesa Quad preamp - I guess that's kinda what it was designed for

Personally, I wouldn't bother pulling 2 tubes, it doesn't greatly reduce volume and for me it reduces the sound quality too much.

I had earmarked my amp for sending to Dan Gower for the Jose mod but haven't heard from him for 6 months so I wonder if he's snowed under.

It's a great modding platform because it has the extra channel with it's preamp tube, volume controls and inputs - no need to drill holes. The world is your oyster.

It sounds like our tastes are different so the only advice I would give is to install a master volume, see how you like it and go from there.

If you like the sound of a 100watter cranked, I'm afraid it's quite hard to replicate that at bedroom levels. Also, you are right on the limits of that Weber attenuator - your amp is capable of putting out considerably more than 100w. Be careful.

Ok, noted on the tubes front - your the second person to say its not worth bothering - thanks.

I found Dan Gower on Youtube, thank for the that. I think its the wrong direction for me to go but interesting none the less!

You say its a great modding platform - thats what I keep reading. I want to enjoy it basically. I bought the Origin Effect Revival Drive over Christmas and oh man, its so good through the SUPER PA with a little compression. I am starting to reside myself to the fact that if I could take the insane amounts of volume down a bit, so the amp opens up more and I can push the volume to 3-4, then I can get more tonal range out of it. The attenuator gets warm with the amp on tick over.

I have to say its been a long time since I used it and its sounds MASSIVE. I mainly play through a Fender Princeton at home (15w) but after an evening playing some Zeppelin / Stone etc I turned on the Princeton and it sounded so small! Its so deep and rich, without all the shrill treble I dislike from the Master Volume series that followed it.

I am getting a local tech to install a PPIMV over the weekend, I am wondering whether this will do the trick.

 

[8bit Barry]

Marshall lists a "100 watt" amp as putting out 170 watts RMS at 10 percent distortion. So, yeah, they're really a lot more powerful than 100 watts. They're nearly double their listed wattage that at full tilt.

Thats really insane. To this day I do not understand how most of the 60' rock guitarists are not profoundly deaf.

 

[neikeel]

Where in UK are you?
This is best supplier in UK:
https://www.ebay.co.uk/itm/Marshall...335109?hash=item5b2fc309c5:g:ChwAAMXQTghRQIWt
What sort of PPIMV is your tech installing?

 

[8bit Barry]

[QUOTE="
The best mod for these (DON'T DRILL ANY HOLES) is to adopt channels 1 and 2 as a 2203. The volume pot for channel 1 becomes the pre-pi master volume (1 Meg audio pot between the treble pot wiper and the PI input).
Next you take a 500pF mica cap and place it in parallel with channel 1 mixer (470k resistor) and ground the other 470k. Then you cascade V2 b into V2a after splitting the cathode to a 0.68uF/2k7 and an 8k2 combination. Use a 470k treble peaker between the stages but my tip is to use a 2200pF (or 1800pF) bypass cap in parallel with this.
Channel 2 volume pot will become the 'gain' pot. Move your NFB resistor (that will be 27k) from the 16ohm tap on the selector to the 8ohm tap.

Next, to minmise bleed between channels I suggest desoldering the green grid wire from channels 3 and 4 and putting a switch in line so that you can connect channels 3 and 4 if you want a flat EQ input for some reason. You can use a SPDT switch in one of the now unused channel 2 jack holes. Save all the parts and wires, including jacks.

That is the simplest best way to get a PA amp to rock at sensible volumes. There are loads of others that work but need more work and explanation.[/QUOTE]

Thats some great technical advice (I dont understand any of it, haha..., only because I am worried about electrocuting myself / healthy sense of death)

- I will pass this over to the tech when I see him tomorrow. We are going to install a PPIMV as a first stage to see if this helps me get some control.

When you say there are loads of others that work, is there a resource you could point me at? I haven't found very much to be honest, just videos of guitarists with modded PA's and no narrative.

 

[8bit Barry]

Where in UK are you?
What sort of PPIMV is your tech installing?

I am in the South West - I am using a tech called Black Magic Amplifiers, recommended by Mansons Guitars.

I didnt know there were different types of PPIMV - should I look at one in specific.

Thanks for the eBay link by the way - appreciated - I have no idea when this silly forum restriction will lift - I cant even reply with your link in the post - I have to remove it!

 

[AlvisX]

I don't like modding or suggesting modding "vintage" Marshalls at this stage of my life ....but yeah , the 2203 style preamp in the PA's is a winner

My version of 2203 preamp in a '68 Major PA.Brite / Peak caps adjusted to taste, dont remember what they are ,but they're lesser than stock



AND the clean channels are great for bass !!

 

[8bit Barry]

Finally I’m able to add some pictures to this post - here’s my 1969 /70 Super PA with an angled 1936 cab filled with pre Rola Celestions - it’s got such a deep smooth sound.







The cab needs some new weave as you can see!

I sorted a PPIMV with Black Magic Amplifiers on Saturday - it’s a superb mod. I’m still running the amplifier through the Weber Mass Lite 100w Attenuator and dialing back the PPIMV by about a third. This means I can lift the volume to 4 / 10 and get a big sound. I’ve been using a Revival Drive for my overdrive tones with a compressor - I cant recommend that pedal enough!

 

[Seanxk]

You know what this means, we need to hear a demo, no pressure lol, I'm still to demo my JTM PA.

 

[8bit Barry]

You know what this means, we need to hear a demo, no pressure lol, I'm still to demo my JTM PA.

You know your right - I’ll try and do a good one not just a tinny iPhone video. I’ve got an SM57.

Here’s the current ‘little and large’ rig...