Marshall plexi?

[beaverbiscuit]

Okay, here I go a'swingin' my ignorance bucket around, sloppin' it all over the ground:

What does the word "plexi" refer to when discussing Marshall amps? I see it all the time but I've never understood what it means. I can't even say that I've ever played a Marshall, actually, and both these issues are making me rather sad. So help lighten my burden, y'all, would ya, and give me the definition.

Or for the philanthropists out there, just send me a Marshall and thus relieve my second problem.

Thanks, folks.

[Tom Hicks]

There was a small plexiglass plate on the front panel of the amp circa 1969 or so.Ergo "plexi".

[beaverbiscuit]

And then they changed it to something else later, I take it. Interesting.

So was there something in particular about the plexis that made/make them desirable to own?

[Tom Hicks]

I'm just a musician with only a smidgeon of geek,so I can only guess.It's the sound they had that knocked everybodys socks off.
I have a custom built tube amp a "mad scientist" tech buddy built for me in his garage,based on a 100 watt twin chassis.Channel one is the '58 Bassman circuit (for bluesy clean) and channel two is the Marshall '69 plexi circuit (for crunch).Except I have EL34s and 12AX7s instead of EL34s and EL84s.I also tried 6550s in it,but the sound was too modern "high gain" for my taste.

[Doug H]

I think they were twin gain stage amps with a little less overdrive than the jcm800. Think ACDC, Jimi Hendrix (without the fuzz) early British punk rock etc..

[beaverbiscuit]

More good info to have. Thanks, y'all.

I've gotta find out more about tube amps. I've never owned or played one, but I'm really chompin' at the bit to get myself a good low wattage tube amp. So many of the boutique amps bill themselves as being "like a plexi" that I just had to figure out exactly what that means.

Thanks again for the knowledge, fellow strum-sters!

[Tom Hicks]

For recording purposes,you don't really need a monster stack.Many famous guitar sounds have been recorded with little tube amps.The pricey favs are Champs and Princetons and Deluxes.Check out any of the 10 watt range tube amps of the 50s and 60s that aren't Fender.I have a 1958 Gibson GA6 12 watter I bought off a guy for $40.I had new filter caps put in and retubed her,ending up with a killer tube amp for cheap.

[Boots]

In the late 1960's (I believe 67-69) Marshall used a JTM45 circuit that had a higher B+ voltage and more power supply filtering. They also switched from the KT66 tubes to the ever so popular EL34's. Marshall used Plexiglass faceplates (panels) until sometime in late 1969 early 1970. This is where the nickname 'plexi' derived from. Then they switched to a "metal faced" front and back panel but basically kept the same circuit. They just changed some resistor and cap values to get different tones and gain.

But the nickname 'plexi' stuck to this circuit and people still refer to these amps as "Marshall Plexi's." Most people also only consider the pre-PCB amps to be plexi's.

Plexi's are usually considered non-master volume. There are mods that make these a master volume, but that's not a 'plexi' in my book.

Edit . . .

To answer your question on the boutique amps comment, the nickname 'plexi' also refers to the circuit mentioned above. There are boutigue amp manufacturers that make the original plexi circuit using point-to-point wiring. These amps are expensive, partly due to the extensive labor involved.

Most amp manufactures based their circuits after the plexi circuit. Orange and Hiwatt to name a couple.

It's a popular belief that Marshall used the Fender Bassman cuircuit as the basis for their 'Plexi' circuit. Anyway, I hope this helps and doesn't confuse you.

[Tom Hicks]

Jim Marshall freely admits using the bassman circuit as the basis of his design.For whatever reason,Fender amps were extremely hard to come by in Britain at that time and he was trying to create a substitute.The use of English EL tubes in place of the 6L6s and 6V6s made a big difference in the sound between the two designs as well.According to Pete Townsend,he collaborated with Jim Marshall in coming up with the "stack" format that eventually emerged.

[beaverbiscuit]

TH, I read about the Pete Townshend thing. Seems he wanted Marshall to build him an 8x12 for more power, but the cabinet would have been too heavy to move easily. So Marshall opted for two 4x12s that could be stacked one atop the other. And thus history was made, eh?

BTW, I realize I don't need a stack to get a good tube sound. I'm actually looking for something 30 watts or under, preferably something even under 10. I've looked at the Univalve, and I'm intrigued by Mojave's Coyote head, but I'm still looking. I just wish that I could find something locally that I could actually play, because I don't want to base my decision on MP3 samples.

And thanks, Boots, for the extra info. It was helpful and not at all confusing.

[lesterpaul]

you're sorta right ,marshall did build him an 8 speaker stack but he only had it for a little while th roadies couldn't pick it up ,he took it back an they sawed it in half ....eric clapton wanted an amp that could fit in a car easily an that is where th combo marshall came from ...my source is GUITAR WORLD from about 4-6 issues back ...he also says in there that he looked into th back of a Fender to figure out th wiring at another shop ....

also most of th first Van Halen albums were done with a PLEXI Marshall in conjunction with a variac ....he credits this as th Brown Sound ....................



later

[Boots]

Actually, both Leo Fender and Jim Marshall based their circuits on the Western Electric Circuit. The Western Electric Circuit is what Leo used in his first '59 Bassman. Jim used that circuit in his JTM45 in the early 1960's. I would imagine Jim used it because the Bassman was popular at the time, who knows. American amps were hard to get in Europe in the 60's. That's how Marshall got started.

In the hay days of tubes, tube manufacturers would offer free schematics to people so they would build amps and buy their tubes. The tube manufacturers thought it was a good way to sell their tubes. That's how the Western Electric Circuit was born. The granddaddy of today's tubes amps. hehe


Beaver,

I'm not sure how much spare time you have or what your interests are, but you can get into building your own amps. A good place to start is www.ax84.com . The also have links to places that sell kits that you assemble yourself. Most of their amp designs are low watt tube amps, perfect for home use and recording. You can get tube saturation at low volumes. Doug Hoffman has a more involved site at www.hoffmanamps.com .

If you have any questions on home brews, send me a message. I would be happy to help you as much as I can. I built my first 50 watt plexi a while ago, it was a great learning experience.

If you don't want to build, Greg Germino (www.germinoamps.com) has a new 6V6-based head at 30 watts. It has the 'plexi preamp' with a 6V6 based power amp. But 30 watts of tube power is still LOUD. He has a link that has some videos and sound files of him playing that amp.

Good luck on your search.

[Aaron Cheney]

I got to meet Jim Marshall about two years ago and he ran down the whole plexi story for me, as well as confirming the Pete Townsend thing. It was a blast to hear him talk about the olden days and refer to all these guitar gods by pet names like "Petey" and "Jim".

Aaron
http://www.voodoovibe.com

[beaverbiscuit]

Hey Boots, thanks for the links. I actually have the ax84 site marked as a favorite. I've been in touch with Chris Hurley, the guy who runs that site and its sister site, Doberman Amps.

It's not so much that I'm not interested in building my own amp — actually I think it would be tres cool — but rather that I don't know if I have the time and patience necessary to climb that learning curve. And from what I see posted at the ax84 site, most builders advise against building an amp as a first electronic project, since there is the possibility of accidentally killing yourself if you goof. That's just what I need to do. Oh, and then to also have to build the enclosure for it — I don't know, it just seems almost insurmountable with my limited abilities in the world of "hands on."

BTW, I checked out the Germino link. Pretty cool. The video samples of the actually builder at play are a great idea, and the amps sound pretty good.

Thanks again.

[Littletrigger]

Originally Posted by Boots

But the nickname 'plexi' stuck to this circuit and people still refer to these amps as "Marshall Plexi's." Most people also only consider the pre-PCB amps to be plexi's.

Plexi's are usually considered non-master volume. There are mods that make these a master volume, but that's not a 'plexi' in my book.


Most amp manufactures based their circuits after the plexi circuit. Orange and Hiwatt to name a couple.

It's a popular belief that Marshall used the Fender Bassman cuircuit as the basis for their 'Plexi' circuit. Anyway, I hope this helps and doesn't confuse you.

Ok, a lot of guys/gals here know their stuff about recording but a lot less about the actual equipment that goes with the instruments . mainly vintage stuff. I will straighten this "plexi issue" out hopefully.

Marshall was a music shop in Bletchley, which is north of London, sometime in the 60's Jim Marshall started making amps, the general basis of these were fender circuits. One day, Pete Townsend walked in, and slapped down his bassman, he asked for that amp to be made twice as loud and twice the size, Jim obliged and the Marshall stack was born. All these early amps had a plexiglass front to them, thus donning the name "PLEXI" and were originally based upon the jtm45's rip of the bassman circuit.

Marshall then went on to create a series of amps under the "plexi" name (please note that they were not referred to as "plexi" at the time.) these included, the jtm 45, jtm45 100, superlead, superbass, major, PA100 etc.... And this continued happily right through the 60's. About June or July (I think)
of 1969 Marshall fluently ditched the plexiglass fronted chassis, in favour of the modern brushed aluminium one we have today.

Although the chassis changed, the circuits made little in the way of immediate evolution, Most Marshalls had their circuits alter by the week at the time in terms of capacitor values etc... The reason Plexis are more expensive is:

a) their exclusivity, they are more rare, and they are older.
b) most artists favour and used only plexi models (despite what they may have been endorsing for Marshall on stage, i.e. Angus young, evh (in the studio), Clapton, Hendrix........
c) The general myth surrounding them.

Marshall then went on till 1974 making tag board ptp wired amps, after which they moved to pcb.

Most people use "plexi" annoyingly freely, like to con people on eBay and the like, since not many people seem to cotton on to the real value of old Marshalls, not saying plexis are better though, I own only aluminium metal faced 70's Marshalls now, I sold my 67'superlead for an astonishingly large amount, and I didn’t really rate it as much as my 77'. Its all personal choice.

As for oranges and Hiwatts nicking marshal’s circuit, that is really, well, wrong. Hiwatt was Dave Reeves and Harry Joyce's company that evolved from Sound city, in the mid-late sixties the sound city circuit is nothing like Marshalls, in fact Marshall amps were mainly using kt66's when sound city were building their el34 based mark1 100's, and sound city is a massively clean, uncompressed amp, much like hiwatt, this cannot be said for Marshall. If you just plug into a Marshall and a hiwatt you can feel that they are totally different. Oranges are similar in feel to Marshall, but yet again a totally different animal.

hope that clears some of that up.