What is 68 Plexi so Revered?

[MistaGuitah]

It seems like the 68 plexi is the most sought-after Marshall plexi. Why is that? I don't know much about Marshall history, but the way it was explained to me is that 65 & 67 plexis are favored by people who like Hendrix, AC/DC and older tones; the 68 is like the holy grail Marshall circuit that departed from the Bassman circuit; and the 71 is like the 100w beast that took over rock for a decade. I was also told that it's better to get a 68 or later because the 67 and earlier plexis are very inconsistent, or basically 1 out of 10 sound awesome.

It seems like a lot of replicas and clones are based on the 68. What is it about the 68 circuit that makes it so desirable? Specifically, how would you describe the tone like low end, presence, gain, dynamics, etc?

 

[311splawndude]

(waits patiently for Michael R/T, scottosan, 46&2, Racksystems, etc)



...and why did Jim add the plexiglass panel? Was it because it was easy to cut and affix or did it also add some level of safety? I guess I always assumed both but always looking for confirmation

 

[Ratou]

because that's the one Eddie Van Halen had

 

[psychodave]

I own an original 1967 plexi. Nothing sounds like it. The clones are close, but never exact. Once you hear the sound in the same room you can’t forget it. 1968 is similar, just slightly different due to Marshall constantly evolving.

 

[cardinal]

I think the general idea is that '67 and earlier used a shared cathode on V1a rather than the split cathode that seemed to settle in around '68 (though Marshall might have used either shared or split around this time). The value of the split cathode and some associated changes made the lead channel brighter and meaner sounding as it was cranked up. Some additional tweaks were made over the years (tweaking the values of the split cathode, eliminating the cathode bypass cap around '72 but instead increasing the negative feedback, etc.).

But generally I think people like the '68 because of some guy named Van Halen that you might have heard of.

As for inconsistencies, there's really no magic involved. At this point, many of the caps might have drifted badly or just cracked and failed, so if you're going to be playing it, it's realistic to expect to have to replace some of the components and if done well, shouldn't really impact the value to another player. And at that point, if it doesn't sound as smooth/aggressive/whatever to you, just tweak the component values until it's "one of the good ones."

 

[glip22]

Clones can't quite get there because of the old iron. For some reason those old trannies add the extra sauce.

 

[Racerxrated]

For the metal face JMPs the 72s are the ones to get, from what I've read....

 

[controlled_voltage]

i thought germino and mettro cracked the code?

 

[marvcus]

because that's the one Eddie Van Halen had

This. People want a Serial No. SL 12xxx because that is the batch around what EVH's amp was, and his was a 1968 100w Super Lead.

Never played a clone, but I have a 1969 100w plexi and it is magical.

 

[DragonCrestPC]

i thought germino and mettro cracked the code?

I would also like to know if they did. I've wanted a 67/68 plexi for a long time but everyone charges an arm and a leg for one with most of them falling apart as the amp is old as hell.

 

[LP Freak]

Like already said, the clones sound good and close but they’re not quite the same even with NOS parts so it’s has to be in the old trannys.

 

[cardinal]

For the metal face JMPs the 72s are the ones to get, from what I've read....

My theory on that is that in ‘72, it would be conceivable to have gotten an amp with both the cathode bypass cap and the low negative feedback set up. That’s how I’ve set up mine (not stock) and I think it’s a fire breather. Before ‘73, most ran higher negative feedback and post ‘72, the bypass cap was gone.

 

[glip22]

For the metal face JMPs the 72s are the ones to get, from what I've read....

My theory on that is that in ‘72, it would be conceivable to have gotten an amp with both the cathode bypass cap and the low negative feedback set up. That’s how I’ve set up mine (not stock) and I think it’s a fire breather. Before ‘73, most ran higher negative feedback and post ‘72, the bypass cap was gone.

What you are saying plays a role but the biggest factor is if you find one with that high plate voltage power transformer. My 73 puts 520 on the plates.

 

[Racerxrated]

For the metal face JMPs the 72s are the ones to get, from what I've read....

My theory on that is that in ‘72, it would be conceivable to have gotten an amp with both the cathode bypass cap and the low negative feedback set up. That’s how I’ve set up mine (not stock) and I think it’s a fire breather. Before ‘73, most ran higher negative feedback and post ‘72, the bypass cap was gone.

What you are saying plays a role but the biggest factor is if you find one with that high plate voltage power transformer. My 73 puts 520 on the plates.

And that must be what is going on with some 82 2203/4s, I've had a bunch of 800s but every damn 82 has been a beast, 50 or 100w. Every one.

 

[psychodave]

For the metal face JMPs the 72s are the ones to get, from what I've read....

Every 72 SL I’ve played has been crazy bright. I sent mine off to Cameron for an Aldrich mod and the amp is insane now.

FWIW, my 67 has 550+ plate volts. It’s massive sounding. It’s actually a super bass and I added a bright cap to the volume pot.

 

[Wizard of Ozz]

For the metal face JMPs the 72s are the ones to get, from what I've read....

Every 72 SL I’ve played has been crazy bright. I sent mine off to Cameron for an Aldrich mod and the amp is insane now.

FWIW, my 67 has 550+ plate volts. It’s massive sounding. It’s actually a super bass and I added a bright cap to the volume pot.

My original 1967 SLP is also putting out over 550+ volts at the plates. It’s a killer. I’d put it up against any stock Marshall from 68-73. Germino, Metro, et al just don’t sound nor respond the same.

 

[Rick Lee]

I had a bone stock '72 50w. It was glorious. But I also have a 2016 1987xl and I really think it sounds just as good. I needed the money, got them both for a song, so flipped the '72 because it was worth a lot more. I still love, love, love my 1987xl, and I don't have to worry about dinging it up at band practice and gigs, and can always replace it for pretty reasonable money.

And '72s are so desirable because that was the last year of the hand-wired boards. But the first few months of the 73s were also hand-wired. They sound the same as the 72s. It's just that, with a '72, you know it's hand-wired. With a '73, you need to pull the chassis and check. I will probably grab a '73 one of these days when I find a hand-wired one for the right price.

 

[Racerxrated]

I had a bone stock '72 50w. It was glorious. But I also have a 2016 1987xl and I really think it sounds just as good. I needed the money, got them both for a song, so flipped the '72 because it was worth a lot more. I still love, love, love my 1987xl, and I don't have to worry about dinging it up at band practice and gigs, and can always replace it for pretty reasonable money.

And '72s are so desirable because that was the last year of the hand-wired boards. But the first few months of the 73s were also hand-wired. They sound the same as the 72s. It's just that, with a '72, you know it's hand-wired. With a '73, you need to pull the chassis and check. I will probably grab a '73 one of these days when I find a hand-wired one for the right price.

I also heard Yngwie used to hoard up all the '72 50 watters he could put his hands on because they were the best sounding for his style. I did have one 72 1959 and like Dave said, it was REALLY bright.

 

[MistaGuitah]

I knew EVH used to play plexis but I thought he used the 100w Superleads, had not idea he made the 68 plexi famous. What about the diode rectifier thing? Was that something introduced with the 68?

 

[Wizard of Ozz]

I knew EVH used to play plexis but I thought he used the 100w Superleads, had not idea he made the 68 plexi famous. What about the diode rectifier thing? Was that something introduced with the 68?

Eddie played a 1967 SLP... not a 1968. I own the same make and model year amp.

A 1967 SLP is a "Plexi" in the colloquial sense of the word... 1967 Super Lead Plexi model #1959.