Perfecting the Lead 12

[21fret]

Mine just collects dust. I can't get along with the stock speaker. I should track down a G10L-35 then I'd probably use it.
I modded for an external output jack, so atleast I can use it with an external cab!
I'm familiar with the 1965 (& 1966) cabs, but there are 2 types of drivers Celestion used for that model and little to no info on the larger driver.
Marshall has used this speaker for Bass and Keyboard.

 

[TassieViking]

4 ohm impedance would let too much power flow through the output transistors and is not a good idea.

I think I have to completely disagree on that, the power transistors can easily handle the 4 ohm load.
But you would have to replace the power transformer with a bigger VA one, the lead and bass 30 uses basically the same power amp and is 30 watt at 4 ohm, but with a bigger power transformer.

The transistors can handle 10 amps, 80 volts and dissipate 150 watts each, they could easily be used up to a 100watt amp with the correct design and huge heatsink and power transformer.

 

[Sepp]

Late to the party on this thread, but great to read. Mines just been sitting for a few years, and this is the motivation to give it some love.

 

[DirtySteve]

I need to fix mine. I swapped in a new speaker and it stopped working, I don't know why, I just set it aside.

 

[fitz]

I need to fix mine. I swapped in a new speaker and it stopped working, I don't know why, I just set it aside.

Check fuses?

 

[DirtySteve]

Check fuses?

Would the power light still come on if the fuse is blown? I haven't check it and it's buried right now under a bunch of stuff, maybe tomorrow. The reason I just put it aside is because I thought something was wrong with it already from the get go (I bought it used last year) and I was hoping it's just the speaker, but I tried a few before the last swap when it died. It's very bright and harsh, judging by mine I don't get why people here seem to think so highly of them so I really think there was already something wrong with it.

 

[AlvisX]

I don't get why people here seem to think so highly of them so I really think there was already something wrong with it.

It's a rock n roll tone machine , man !
and a proper Marshall



Un-mic'd
Club owner is a friend , recording engineer, bass player in a couple bands together
He doesn't mic guitars in that room. I respect his opinion . He said that Lead 12 was loud.
It aint no toy , nor " practice amp"


Mic'd , theater sized venue


They're also sensitive to impact against them pots
A guy laid mine on it's back ,in a van . Other stuff from the load was putting pressure on my pots
I got to the FCKN Fillmore and my amp was cracklin and cuttin out
Had to re-flow all the pot / jack connections the next day .....good as new

 

[DirtySteve]

It's a rock n roll tone machine , man !
and a proper Marshall







They're also sensitive to impact against them pots
A guy laid mine on it's back ,in a van . Other stuff from the load was putting pressure on my pots
I got to the FCKN Fillmore and my amp was cracklin and cuttin out
Had to re-flow all the pot / jack connections the next day .....good as new

Yeah, mine never sounded that good.

 

[svinyard]

Yeah, mine never sounded that good.

My amps have the same problem.

 

[AlvisX]

Yeah, mine never sounded that good.

Well, my Bass 12 is having input jack issues ,where it goes dead silent, so I wouldn't rule out pot / jack solder joint issues in your case

 

[DirtySteve]

Well, my Bass 12 is having input jack issues ,where it goes dead silent, so I wouldn't rule out pot / jack solder joint issues in your case

I cleaned the jacks and pots when I first got it, it helped, but not much. The pots are very loose and scratchy. I thought about replacing them, but I don't know if I really want to put that much effort into it.

 

[AlvisX]

I cleaned the jacks and pots when I first got it, it helped, but not much. The pots are very loose and scratchy. I thought about replacing them, but I don't know if I really want to put that much effort into it.

I wasn't talkin about cleaning , I was talkin about loose / broken solder joints .....what appears to be a fairly common problem

 

[DirtySteve]

I wasn't talkin about cleaning , I was talkin about loose / broken solder joints .....what appears to be a fairly common problem

Ah! Sorry, I didn't catch that. my bad. I'll check them, thanks.

 

[Dino Boreanaz]

I had some cutting out and cracking from the low input on my Lead 12 which I suspected was caused by bad solder joints. So I re-flowed the connections on both input jacks about a year ago and it's been absolutely solid and reliable ever since.

With the jacks and pots being mounted directly to the PCB as they are on these amps, it's critical that the mounting nuts are tight on these components so that the solder joints are not stressed by small movements while plugging in, unplugging, and adjusting controls. As these amps are approaching 40 years old, it's probably worthwhile checking them all and tightening any that have loosened over time.

 

[BeardedRetroGuy]

I don't often play on my Lead 12, but it's kind of a beast. I took out the Celestion G10D-25 stock speakers out of my Lead 12 Microstack and replaced them with Celestion G10 Vintage. It's got a HUGE mid-range honk now, but you can dial that back. Completely tames the harsh high end the G10Ds had and has an aggressive bark when cranked.

I also wanted to dress up the head and cabinets to make them look a lot more like the "real" amp heads and cabinets, like my JVM410h half-stack. So I got with a metal sign company and we made a new faceplate and some small cabinet badges that I was able to put on after searching for a long time online for the badge holders that go on Marshall speaker cabinets. Check them out:



Then I replaced the main swich that had a nice modern curve to it with an older-style angled switch you see in the above picture. I wanted it to feel like a much older amp. It lights up just like the old one did, but this switch matches what I see in a lot of pictures of the Lead 12 amp.

Here's the back of the amp where I replaced the black nuts with red ones to indicate the speaker output.


And if anyone is interested about the inside, this is it:

As you can see, when I removed the original switch (which was soldered on), I capped the ends of the wires with C-clips so I could more easily swap out the power switch in the future if it ever became necessary. Also, all ofthe pots on the front of the amp had plastic spacers that I ended up removing in order to add on the new metal faceplate.

No, some of the text on the faceplate doesn't precisely line up with the dials and switch, but it's a prototype and it cost me nearly $100 USD and I don't feel the need to redo it. The original "orange" sticker is still on the amptray BEHIND the new faceplate.

 

[AlvisX]

I don't often play on my Lead 12, but it's kind of a beast. I took out the Celestion G10D-25 stock speakers out of my Lead 12 Microstack and replaced them with Celestion G10 Vintage. It's got a HUGE mid-range honk now, but you can dial that back. Completely tames the harsh high end the G10Ds had and has an aggressive bark when cranked.View attachment 155480

I also wanted to dress up the head and cabinets to make them look a lot more like the "real" amp heads and cabinets, like my JVM410h half-stack. So I got with a metal sign company and we made a new faceplate and some small cabinet badges that I was able to put on after searching for a long time online for the badge holders that go on Marshall speaker cabinets. Check them out:
View attachment 155481
View attachment 155482

Then I replaced the main swich that had a nice modern curve to it with an older-style angled switch you see in the above picture. I wanted it to feel like a much older amp. It lights up just like the old one did, but this switch matches what I see in a lot of pictures of the Lead 12 amp.

Here's the back of the amp where I replaced the black nuts with red ones to indicate the speaker output.
View attachment 155483

And if anyone is interested about the inside, this is it:
View attachment 155484
As you can see, when I removed the original switch (which was soldered on), I capped the ends of the wires with C-clips so I could more easily swap out the power switch in the future if it ever became necessary. Also, all ofthe pots on the front of the amp had plastic spacers that I ended up removing in order to add on the new metal faceplate.

No, some of the text on the faceplate doesn't precisely line up with the dials and switch, but it's a prototype and it cost me nearly $100 USD and I don't feel the need to redo it. The original "orange" sticker is still on the amptray BEHIND the new faceplate.

I put those in my micro stack as well......marvelous !

 

[Filamentary]

Hey folks. I had a Lead 12 Stack I messed with 20 years ago. Great amp I really enjoyed it and I wish I still had it. Here is what I did to mine…

I put two 12” G1275 T’s (from a 4211 combo) in the little cabs, I didn’t even re-cut the baffles. I just screwed them in there. It was fine. Occasionally I used the little cabinets on gigs with other heads. And played a couple gigs with just the lead 12 head too. Of course my ears are more discerning now, and I would probably re-cut the baffles because I can. But I certainly wasn’t tone deaf back in the day either, and as I recall it sounded good.

I know I tried a bunch of different op-amps. I remember settling on a NOS JRC4558. I had some because that was the “magical” Tube Screamer op amp that everyone wanted at the time in their drive pedals. The chip is socketed. I am sure the difference wasn’t huge. I feel like it did smooth things out a little bit though. Very easy to try!

I don’t think I messed with anything else in there.

Well, please know that I am envious! Hang on to those lead 12’s…