I'm going to chime in here also since I also had a pair of plates. Back in the late 1970s and the other in the early 1980s.
It was created in 1958 by DR. KUHL. When EMT made these cold rolled steel plates... due to imperfections, 60% were rejected.
Since these plates are very prone to rust. They were originally coated with linseed oil. Which kind of makes them, at this age, stage, vintage look pretty nasty. And where some uninformed, mindless engineers, cleaned off those horrible sticky, dusty, dirty icky things. And then whoops... the next time you open the box to tweak the plate, it's all rusted! So it's not designed to look pretty. And you don't want to clean the plate, of anything.
Secondary information was that a single nut, at 2 of the 4 corners, were to be turned counterclockwise, 1/4 turn, before ever moving them. And upon moving them, if you were lazy? You only needed to tighten those to back up, one quarter turn. But if you were good? You would tune all 4 corners.
Now the tuning instructions for those metal strap and piano string clips, coming from the Germans, was rather goofy LOL. Almost too goofy to believe? The basic instruction was to tighten them, until the piano string wire clip, snapped and broke. Then you were to put another one on to replace the broken one. Tune up almost as tight. But not quite as tight. LMAO that is the most imprecise set of German instructions/directions, I've ever read LOL.
As seen in that 1st video, he was tuning his with a torque wrench. I tuned mine, by ear, in a similar way to that of a violin. They had to be the same pitch on all 8.
They were also offered with and without that top motorized version and the manual hand cranked, non-motorized version. They originally cost about $5000. The 1st ones used tube circuitry and were mono. The later transistorized ST versions were of course, stereo. The pickups were basically akin to a child's record player with a crystal cartridge. That's a crystal pickup. Later modifications by others replaced those with Barcus Berry & FRAP, pickups. In the early 1970s a few enterprising folks stuck 4 pickups and 2 more amplifiers for quadraphonic. Today you could certainly go really crazy and stick on 6, 8 or 10! Or 9 if that Tickles your fancy?
Yes the corners of the steel plate can be damaged. It's happened to others. They can generally be shored up and fixed. With the help of a little spot welding and reinforcements to the corners.
It should be also interesting to note that no 2 ever sounded alike. And even some badly rusted ones sounded better than others in pristine condition. And those were the plates of the 40%, that weren't rejected. So the rust is not necessarily a dealbreaker. But you're likely going to have to accept less?
I have found the going rate for these to still be up around $2500 in decent condition. Considering their age, they have certainly held their value.
One of the interesting things that gave these Plates their sizzle. And they did have this really cool sizzling sound to them. Some folks hated that. Others love that. I loved it. To me that was the defining sound that separated EMT Plate reverbs, from everything else. Part of that sound is inherent to the plate itself. It was further enhanced, in that in the drive amplifier, similar to that of a record-Cutting head, a huge amount of high-frequency preemphasis, was being driven into the driver. This also helped to modify the high-frequency RT 60 to that of the lower frequencies, extending them.
The change in the reverb time was done by that white hunk of a chunk of basically fiberglass ceiling tiles. And the damper, even at the shortest reverb setting, never touched the plate. I believe you had a dial in the adjustment distance of approximately 1/8 inch, at the shortest time, from touching the plate. And when fully retracted from the plate, RT 60 was 4.5 seconds. Then we had fun gating that. That was the 1980s that popularized that sound. I think Bob Clearmountain jokes about adding too much to his snare drums back then and laughs about it, today. Or so he has said to me and others.
Some folks even went as far as replacing the driver amplifier. Lots of folks felt that basically, the EMT driver electronics, was underpowered. So you can have more fun testing and tasting different drive amplifiers. Try a Macintosh compared to a Crown. And then use the equalization network of your choice to add whatever preemphasis you want. There is no deemphasis on the pickup electronics. If memory serves me correctly? Memories are fading. My last plate went away in 1993.
Another interesting addition that was in the EMT drive electronics was that of a switch on the circuit board. This switch engaged a 2:1 compressor on the drive amplifier. And throughout the years that I owned them and used them, I would occasionally switch it on and occasionally switch it off. Most of the time off. But frequently on. And I never really developed any particular preference to be just either way. Why that switch was not included on the remote control? I'll never know? It would have been so much more convenient. Some of these things were suspended by springs from ceiling rafters 23 feet up above the floors. Mine were all at ground level. The 1st one I didn't have an actual room to put the EMT plate into. Because they were electromechanical devices, they were also extremely susceptible to any ambient surrounding noise. Not installed correctly, you could hear conversations going on in surrounding offices LOL. And that made for a spooky sounding mix LOL. It was like WTF is that? It's a poltergeist in a reverb plate! And then everybody goes screaming running out of the control room. So we just built a huge insulated wooden box on rubber grommets to stick the plate into. And that just sat off to the side of the entry Bay. You couldn't have any traffic coming or going, near that thing, when you were using it.
I think the patent expired in 1982? Upon its expiration, a few other companies started making knockoffs. Some didn't like the idea of a 60% rejection rate of the cold rolled steel just to get a good sounding reverb. So, stainless steel was tried. It was wild sounding! And the rejection ratio was extremely small. Which made the manufacturing of those much more attractive. And no need for nasty sticky dirty linseed oil. So my 1st plate was the EMT 140 ST. My 2nd Plate, was the big Studio Technologies of Chicago, stainless steel plate. And if you think an EMT is bright sounding? You ain't heard nothin' yet. It was a bit bright for Opera. And I did a fair amount of Opera. So you needed to mush that down a bit. I tried stuff like EQ and duct tape on the plate LOL.
Something else not completely intuitive about how they work. You'd think that with the driver connected, physically, to the steel plate, that the reverb comes from the plates vibration laterally? As in back and forth from, essentially the cone of the speaker that was screwed to the plate. But that's not how it worked, no. The sound actually travels longitudinally, from corner to corner, edge to age. Like dust blowing over a highway. And not an earthquake. Which would be lateral excursion. Or did my brain damage get my nomenclature, backwards? I don't think so? Any who... there are also some YouTube DIY videos how to make your own. Not just any cold rolled steel will do. Some can be so bad as to sound like you simply have stretched out your old trashcan. And used that. Yuck. Then you're better off with digital limitations. I mean imitations, emulations, DeForest Kelley. He's dead Jim!
Lying them down like your mattresses ain't the way they should be. That will definitely destroy the alignment with the driver. More so than it will for pickups. Either way you don't want that to happen. They should be stored edge on side or bottom. They can be mounted vertically. Though most of the time they are mounted horizontally. They actually take up more room that way.
Also connected to the boxes, at both ends are a pair of metal plates extending outside the box with a pair of holes in them. These can be used to hang and mount them that way. But they were actually intended to stick a couple of round woodendowels through them. So you could get 4 people to move the thing. Though most folks just used 2 burly guys. Who really weren't burly because we were all recording engineers LOL. That's okay, it wasn't something you would move around often. They're not meant to be moved. Not really. Any bending or flexing of the frame and you've got 350 pounds of worthless reverb.
Improperly moving the plate without the one quarter turn loosening at least 2 of the corners, can cause a corner support pair of clips to break and bend the corner of the plate at one of the corners. But if you're real real careful? You may not sustain any damage? But why find out? It's like tuning a guitar. You tune it when you get it even though the factory did it before they shipped it. That don't make it right LOL. So tuning it is an art unto itself. And everybody thinks they know the best way to go about tuning a plate. So do I. Of course... I'm the one that's right LOL.
When I started my truck in 1991, I was thinking about trying to get one of the EMT gold foil, 240's. The demonstrations I heard made this one 6th sized gizmo in comparison to the 140 make you long for one. They were stellar sounding! But they were right on the cusp of the EMT 250. I don't think many were made and I don't think many were sold? I thought it would be great to have one for my truck instead of those dismal digital thingies we all use. I've only seen one used extremely broken one. It looked like it may have been the only survivor of the World Trade Center? It looked like it fell 3 stories to the concrete. Not even worthy of parts.
Someone like myself might be thinking, I wonder if one of those ones you have may have been one of my former EMT's? Did you by any chance find a little chunk of some black hash? Then it's probably mine? It worked wonders for tuning. By the way... I might have a nice bridge for sale you'd like?
(I can't help but think... I'm moving to Austin, by summer. Maybe we should talk? 202-239-7412 and please leave me a message. I miss mine so bad. And the ones I didn't own and used. I know we can work a deal .)
Help Me, help me... I'm melting ;-)
Mx. Remy Ann David
