Headfirst had a similar era amp on the bench in a recent video. They also made 10K resistors with bigger values in parallel. Definitely stock. I'm really looking forward to this - I just impulse purchased a 1975 JMP 50 W (the 1986 model number I believe) recently, and I've been wondering what to do with it. It's less stock than this amp, so it could be in for a conversion. It sounds absolutely banging - clean, loud, dynamic. It's very demanding to play versus amps that compress more. I can only turn the volume up till it generates a signal, then my neighbours can already hear a bit!
Crank the Treb, Mid, Pres and keep the Bass off and my stock 70 Super Bass has plenty of bite. Doesn’t have the aggression of the Lead spec amps so you lose that ripping paper sound, but for vintage style guitars(especially a Strat) a stock Super Bass is already ideal
What an awesome amp! While not as collectible or easy to work on as earlier p-p ones, they still sound terrific. The cabinet with G12Ms was typically a guitar cabinet. I am curious to see how it comes along.
Lovely looking amp and cab. Video and editing are top notch, great work! As others have said, they were probably short on 10k resistors the day it was built and they weren't going to stop churning these out. Definitely came out of the factory like that.
Actually a have a large stash of the original Arrow 'Made In England' black bat switches. I sold a bunch of them about 10 years then backed off as my stash dwindled, but then I found some more I had put up in a box in my closet. Now they really are almost impossible to find... without digging thru my closet that is. I'd say I have at least 30 of them left.
I have a 1974 JMP SUPER LEAD 100. It came with KT-88s 5:38 as it is an American version which I read that they had issues with the EL-84s breaking during shipping to North American so the KT-88 were used. I checked the schematics for both versions and the only difference I noticed was the bias resistor values. I switched the resistor and rebiased the amp with EL-84s. I have since heard that the output transformer should have also been switched. Is that true, if so I will be going back to the 88s.
My 74 is also an American version that came with 6550s. there's a sticker from the factory, on the chassis stating this. I changed the bias resistors to 220K and now I use EL-34s. No need to change the OT.
Nice mate, this will be fun to hear the end result. They are killer amps when at their best. Jason (Headfirst) ironically had an amp on his bench not long ago from a similar era where the 10Ks were also set up with this parallel situ of a 22 and 15k. A shortage at the factory is my guess. Will be watching intently on this one mate, she's in good hands, of that Im sure.
On behalf of all serial victims of bodgers, left struggling to keep their chins up ~ thanks for putting these videos together Brad. They're valuable resource for many and varied reasons. The trouble you take is appreciated.
Sweet, Brad! That is a killer project! Its not in too bad shape, though it looks like it was dropped at least one time. Tough amps for sure! My Marshall JMP is a 76 one of the first master volume 2203s... so I'm really looking forward to seeing what you can do with this Super Bass!
Brad I can't wait for the follow up video(s), I just bought a fairly unmolested 1970 SB but does have an added Master volume which I'm def gonna keep! I am going to go ahead and change mine to SL spec. And mine has the painted solder joints everywhere which kinda makes you want to not touch the thing on the other hand! LOL
Brad what's up with the SB? Did you get it done? I am really interested in how you voiced it. I went full lead spec after a couple of months playing with some stock cap values mixed with lead values. Mine came with a simple pre PI master which I liked for the cleans and lower volume with OD pedals but I also added the larMar Post master so I can get full saturation without getting arrested at a decent volume. I know it seems like sacrilege to some, but I can dial down the pre and crank the post and get all kinds of useful amounts of gain per taste go from almost fender clean to full on. Or turn them both up until they are out of circuit. Mine was an export to US with stupid polarity switch and death cap and two prong cord. I kept getting shocked through my grounds if had it wrong direction so I ripped all that out and went 3 prong. In place of the polarity switch I put in the post PI master on the front and a bright cap switch on the back in one of the 4 speaker jack holes. 500pf or 330pf, at lower preamp volume the 330 sounds perfect.
Have you seen the back of the board yet? Any time I see one of these older Marshall boards I have flashbacks of that one Lyle found where all the traces were “re-flowed” and the whole board was burnt to a crisp. I still can’t believe someone did that.
Good to watch Mate .. i`m a Bass player ...dont know techs stuff.. but was interesting to watch.. i`ve duelled with many Marshall player`s in my time .. Strat and LP`s but in my day .. the old AC370 with a Wbin with a 15`` JBL kept up no probs in a big room/hall. Cheers well presented.
As much as I know that’s rare transitional JMP. With toggle switches but with STI PCB. Switches date it to first amplifiers with PCB as well as the usage of the mustard caps. So I believe it’s 1975 built amplifier. Early 1975. Mass production with the ST I PCB started in 1975 and it has also brought big square plastic switches soon after it. This are best sounding PCB amplifiers. ST I PCB was made really good. Though age is doing it in while turret board amplifiers are still going strong. So I saw toggle switches and thought this is amplifier built till 1974 but sadly it is not it. ST I has few options for different models using the same PCB. Also it could be used with mustard caps that were bigger as well with way smaller modern PP and PS coupling caps. Most once I see have modern caps that I am not a big fan of. Amplifiers I saw are often modded beyond any practical need. Most of them have loose cables and damaged PCB as well as holes in chassis. In the principle after the last one I have fixed I am no more fixing PCB amplifiers. Toggle switches , turret board and I can accept people call it a Plexi. PCB, aluminum front plate, square switches, master volume and small caps are not Plexi amplifiers for me even if they use the same schematics. For me personally, all starting from JTM to JMP with turret boards are best amplifiers they have made. Built to last and great sounding amplifiers. I get it they have had to go PCB route because of high demand. They made good PCB too. Still it is more fragile construction than turret board and it was not made to be maintained for ever despite many good techs doing good job restoring them.
I have the last of the plexi's ...1973 Marshall Super Bass 100 with a matching 4x12 with G12H. You say it not loud enough well mine will peel the paint off the wall and I almost imploded my acoustic guitar with the spl.
They did put that anti-tamper everywhere, and the resistors are stock. They ran out of parts a lot so they just used whatever they had. I'd just leave em myself as long as they read 9k or something.
Yes, I also came to that conclusion when I spotted the same colour stuff on some screws. And yes, several others have flagged that they've seen the 8.9k total value with the 22k and 15k in parallel. That must have occurred on quite a few units. Looks like parts procurement was a problem back then as well as in 2023!
Screen resistors look a bit bulged strange for multi watt size. UF5408 would be my choose for diode replacement 3 amp safe range there. Have found grid stops can change sound in HIFI amps . Having said that they are need for safety to stop oscillation . Have been to too many venues where the RF is so high above 2 volts that it is about as strong as the input signal . In NYC have MEASURE 3 plus volts on a wire that was un-grounded so it is a real problem in big cities. For metal players metal film for every one else carbon or carbon film works well as a grid stop. Short leads are the way to go for grid stops closer the better to the socket . Fine work there Brad .
1974 is not a classic. Its a massed produced circuit board amp. 1969 and 70 are the ones that rock.
Oh sorry, my mistake.
I'll just throw it in the bin then.
Thanks mate!
Hilarious
...it will be a classic ine day cos the tone circuit deserves extra prsise too.
You're wrong friend. These amps are absolutely glorious and aren't as expensive as the plexi era.
Funny I haven’t heard a 69-70 that didn’t sound like mush. There is a reason Marshall made changes to circuit during this time.
Oh man so looking forward to part 2, hope you make it.
I Hope Brad Does some follow ups!! Hint Hint!...... Wink Wink!!
I want that cabinet. I love the old checkerboard ones.
WOW! Great day with a long form Brad video on a CLASSIC amp!
New subscriber! Can’t wait for part two
Hey Brad, any update on this one? Was it on a live stream I missed?
Headfirst had a similar era amp on the bench in a recent video. They also made 10K resistors with bigger values in parallel. Definitely stock.
I'm really looking forward to this - I just impulse purchased a 1975 JMP 50 W (the 1986 model number I believe) recently, and I've been wondering what to do with it. It's less stock than this amp, so it could be in for a conversion. It sounds absolutely banging - clean, loud, dynamic. It's very demanding to play versus amps that compress more. I can only turn the volume up till it generates a signal, then my neighbours can already hear a bit!
Thanks for sharing the video overview of the amp. Good job mate and look forward to seeing the work performed on this one.
Crank the Treb, Mid, Pres and keep the Bass off and my stock 70 Super Bass has plenty of bite.
Doesn’t have the aggression of the Lead spec amps so you lose that ripping paper sound, but for vintage style guitars(especially a Strat) a stock Super Bass is already ideal
Nice camera work Bradley. Love this format boyo
Saw some black bat switches on reverb
What an awesome amp! While not as collectible or easy to work on as earlier p-p ones, they still sound terrific. The cabinet with G12Ms was typically a guitar cabinet. I am curious to see how it comes along.
Lovely looking amp and cab. Video and editing are top notch, great work! As others have said, they were probably short on 10k resistors the day it was built and they weren't going to stop churning these out. Definitely came out of the factory like that.
That’s an interesting one !
Aloha Brad! Looking forward to the next video. Mahalo
Actually a have a large stash of the original Arrow 'Made In England' black bat switches. I sold a bunch of them about 10 years then backed off as my stash dwindled, but then I found some more I had put up in a box in my closet. Now they really are almost impossible to find... without digging thru my closet that is. I'd say I have at least 30 of them left.
I have a 1974 JMP SUPER LEAD 100. It came with KT-88s 5:38 as it is an American version which I read that they had issues with the EL-84s breaking during shipping to North American so the KT-88 were used. I checked the schematics for both versions and the only difference I noticed was the bias resistor values. I switched the resistor and rebiased the amp with EL-84s. I have since heard that the output transformer should have also been switched. Is that true, if so I will be going back to the 88s.
My 74 is also an American version that came with 6550s. there's a sticker from the factory, on the chassis stating this. I changed the bias resistors to 220K and now I use EL-34s. No need to change the OT.
@@matttornetta9049 Thanks for the info. I appreciate that we had the same idea and you’re right it was 6550s and EL-34s
love your work mate
Nice mate, this will be fun to hear the end result. They are killer amps when at their best. Jason (Headfirst) ironically had an amp on his bench not long ago from a similar era where the 10Ks were also set up with this parallel situ of a 22 and 15k. A shortage at the factory is my guess. Will be watching intently on this one mate, she's in good hands, of that Im sure.
Did you ever Video a pt2 mate?
Not yet.
On behalf of all serial victims of bodgers, left struggling to keep their chins up ~ thanks for putting these videos together Brad. They're valuable resource for many and varied reasons. The trouble you take is appreciated.
@@BradsGuitarGarageHi Brad, any update?.
Sweet, Brad! That is a killer project! Its not in too bad shape, though it looks like it was dropped at least one time. Tough amps for sure!
My Marshall JMP is a 76 one of the first master volume 2203s... so I'm really looking forward to seeing what you can do with this Super Bass!
I would love a JMP 2203.
They are very sought after over here and often go for $4k or more.
Brad I can't wait for the follow up video(s), I just bought a fairly unmolested 1970 SB but does have an added Master volume which I'm def gonna keep! I am going to go ahead and change mine to SL spec. And mine has the painted solder joints everywhere which kinda makes you want to not touch the thing on the other hand! LOL
Just hold off on those SL mods until we do some sound samples, mate.
A lot of those in the know don't go full SL spec.
Brad what's up with the SB? Did you get it done? I am really interested in how you voiced it. I went full lead spec after a couple of months playing with some stock cap values mixed with lead values. Mine came with a simple pre PI master which I liked for the cleans and lower volume with OD pedals but I also added the larMar Post master so I can get full saturation without getting arrested at a decent volume. I know it seems like sacrilege to some, but I can dial down the pre and crank the post and get all kinds of useful amounts of gain per taste go from almost fender clean to full on. Or turn them both up until they are out of circuit. Mine was an export to US with stupid polarity switch and death cap and two prong cord. I kept getting shocked through my grounds if had it wrong direction so I ripped all that out and went 3 prong. In place of the polarity switch I put in the post PI master on the front and a bright cap switch on the back in one of the 4 speaker jack holes. 500pf or 330pf, at lower preamp volume the 330 sounds perfect.
Hey Brad, as a younger guy I find your work fascinating! Going to be an amazing amp once you’ve worked your magic 😃
I used to gig a '71 Super Bass for guitar - sound guys hated me :D
Such a great circuit though!
Hey Brad, any news on the pt2 vid of this '74 Super Bass?
No.
Listening now. Fantastic
Part 2 will never happen right?
Have you seen the back of the board yet? Any time I see one of these older Marshall boards I have flashbacks of that one Lyle found where all the traces were “re-flowed” and the whole board was burnt to a crisp. I still can’t believe someone did that.
I've had a quick look. All will be revealed on the next episode, but this one is pretty much untouched.
Good to watch Mate .. i`m a Bass player ...dont know techs stuff.. but was interesting to watch.. i`ve duelled with many Marshall player`s in my time .. Strat and LP`s but in my day .. the old AC370 with a Wbin with a 15`` JBL kept up no probs in a big room/hall. Cheers well presented.
nice amp!! ❤
Halfway between super bass and super lead, would that be a super bleed?
Sounds pretty cool to me!
I have a 1973 Super Bass so I can't to see how part plays out and the changes to the circuit, thanks for the content.
Love how the c\lockdown beard stuck around mate lol
Nice
As much as I know that’s rare transitional JMP. With toggle switches but with STI PCB. Switches date it to first amplifiers with PCB as well as the usage of the mustard caps. So I believe it’s 1975 built amplifier. Early 1975. Mass production with the ST I PCB started in 1975 and it has also brought big square plastic switches soon after it.
This are best sounding PCB amplifiers. ST I PCB was made really good. Though age is doing it in while turret board amplifiers are still going strong.
So I saw toggle switches and thought this is amplifier built till 1974 but sadly it is not it.
ST I has few options for different models using the same PCB. Also it could be used with mustard caps that were bigger as well with way smaller modern PP and PS coupling caps.
Most once I see have modern caps that I am not a big fan of.
Amplifiers I saw are often modded beyond any practical need.
Most of them have loose cables and damaged PCB as well as holes in chassis.
In the principle after the last one I have fixed I am no more fixing PCB amplifiers.
Toggle switches , turret board and I can accept people call it a Plexi.
PCB, aluminum front plate, square switches, master volume and small caps are not Plexi amplifiers for me even if they use the same schematics.
For me personally, all starting from JTM to JMP with turret boards are best amplifiers they have made. Built to last and great sounding amplifiers.
I get it they have had to go PCB route because of high demand. They made good PCB too. Still it is more fragile construction than turret board and it was not made to be maintained for ever despite many good techs doing good job restoring them.
Awesome. Bevvie cracked, watching now....
I have the last of the plexi's ...1973 Marshall Super Bass 100 with a matching 4x12 with G12H. You say it not loud enough well mine will peel the paint off the wall and I almost imploded my acoustic guitar with the spl.
What are those heads worth these days?
Very nice
Cool.
I Used to have one of these played guitar through it and am sure it would have blown out my windows if i cranked it up!
Lemmy used one of those.
They did put that anti-tamper everywhere, and the resistors are stock. They ran out of parts a lot so they just used whatever they had. I'd just leave em myself as long as they read 9k or something.
Yes, I also came to that conclusion when I spotted the same colour stuff on some screws.
And yes, several others have flagged that they've seen the 8.9k total value with the 22k and 15k in parallel. That must have occurred on quite a few units. Looks like parts procurement was a problem back then as well as in 2023!
Screen resistors look a bit bulged strange for multi watt size. UF5408 would be my choose for diode replacement 3 amp safe range there. Have found grid stops can change sound in HIFI amps . Having said that they are need for safety to stop oscillation . Have been to too many venues where the RF is so high above 2 volts that it is about as strong as the input signal . In NYC have MEASURE 3 plus volts on a wire that was un-grounded so it is a real problem in big cities. For metal players metal film for every one else carbon or carbon film works well as a grid stop. Short leads are the way to go for grid stops closer the better to the socket . Fine work there Brad .
Metal film for metal players, love it 😅
Oh good, not yet another live stream for me to be 11 hours late for.
Me too!
Gentle Giant
Nice amp, should sound great when You're done.
All amps should be working amps.
If this guy ever quit working on amps he could always get a job as a garden gnome.
My first job would be trimming your mum's bush.
Lol meathead drummer
You no why most bass guitars have fewer strings. Its for dumb guitars that cant have six strings
I'd rather have a working amp than a vintage museum piece amp....