Nothing like a real Plexi

I've had many JMP's from the very early 70's and a couple late 60's plexi's and IMO the 1972 50 watt 1987 were the best to my ears, (with one exception: a 1974 50 watt 1987 MK II I had owned with a MV mod)... insane.

I kept two unmolested, all original 1987's from '72 and '73, (including filter caps) until I bought my Axe. But with the insane volume and lack of practicality for where I was, (and am now), it only made sense to sell them off and let someone else appreciate them for more than being just trophy's in my man cave. Tonally they were very angry amps and with the right drive pedal is what put them over the top and did it for me rather than getting too heavy into the, "really pissed-off amps".
 
The plexi trebble is one of the models I use the most now but I have a feeling I'm going to like the new one better
 
FractalAudio said:
Rather than that 1992 POS reissue I was using (whose output transformer blew up earlier this week).
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NOW i see you true plan: all this Fractal thingy, just to push people to sell all their precious tube amps, and gain access to them for a fraction of the price.
well played, Sir, well played :-D
 
Rocket Brother said:
I hope Cliff will spill the beans on what year, model, output tubes and wattage his new real Plexi is.
I've owned Plexi's from '68, '69 and '73 both 50 and 100 watts versions and a '73 and '74 Super bass, and I can say for sure that although all of these sounded great and like a vintage Marshall should they each had a unique sound. The differences between the KT66 and EL34 or 50 vs 100 watts are definately not trivial IMHO.
Exciting times ahead, though I never found any reason to dislike the current Plexi Treble in the Axe II
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I agree on both points. The plexi in the Axe is still my main patch, so it works really well for me. But those vintage Marshall heads can have various personalities.
Really looking forward to what Cliff has for us...
 
barhrecords said:
I've always thought the 50 watters were sweeter. And when cranked, get more than loud enough too.
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Agreed. One of the main reasons being I could dime 'em and get that patent pending tone without sonically castrating myself in the process.
 
Ok,

I rarely comment in these threads but now I am pumped about the new firmware release. This is the amp model I use non-stop!
 
I remember reading an article written a well respected guitar tech a few years ago (and I think Cliff has said this too) that nearly every plexi sounds slightly different and some can sound drastically different depending on year of production, repairs, and mods that might have happened at some point during the amp's life. I know I've talked to a couple of people who said that no plexi sounds like another. Maybe I wouldn't take it that far. But they definitely do not all sound the same. There are good ones and bad ones.
 
trancegodz said:
The Evolution of the 100W Circuit: From JTMs to JMP Superleads

The 1965-1967 Marshall Super 100 Amplifier (aka JTM45/100)

Every vintage Plexi I've owned or played though sounded different. Only a few of them actually sounded like the ones Hendrix and Clapton used. All those were 100 watt versions.
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First off, parts back then were acceptable if they were +/- 20%, giving a 40% potential swing on each. Then you had those in series, about a hundred of them, so the outcome was always a dicey proposition. Then you have to factor in, Marshall would use whatever parts he could get his hands on to keep production running, so many had out of spec parts from their origin. Today there are far more better sounding Plexis than back then, because by now most have had the wrong parts replaced. Of course another option is a Blockhead 100 which is a perfect clone using parts within 1%, since modern tolerances as so much tighter.
 
barhrecords said:
I've always thought the 50 watters were sweeter. And when cranked, get more than loud enough too.
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I agree, I always preferred the 50 watters for their warmth and sweetness especially when going for natural amp overdrive.
The one exception is a 100 W Plexi I had, that amp was pure Hendrix.
 
james... said:
I remember reading an article written a well respected guitar tech a few years ago (and I think Cliff has said this too) that nearly every plexi sounds slightly different and some can sound drastically different depending on year of production, repairs, and mods that might have happened at some point during the amp's life. I know I've talked to a couple of people who said that no plexi sounds like another. Maybe I wouldn't take it that far. But they definitely do not all sound the same. There are good ones and bad ones.
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Truth. Consistency of components during the prime era of Plexis wasn't like it is today. There was a lot of variation in those amps, as well as similarly aged amps such as the Bassman and a few others.
 
The while the parts tolerance is absolutely true, I have never heard a reissue Marshall that sounded better than one of those old magic Marshall's. And, you can track down the differences. Those differences have much more to do with the transformers, voltages, and to a lesser degree, capacitors, than the resistors. This is a subjective thing because tone is a subjective thing; I have run across some marshall's that have high voltages- up to 460vdc on the el34 plates for a 50 watt amp - even higher on some 100 watt amps. I have seen el34's go into melt down with max bias by simply applying that huge voltage to them. With out fail these amps sound terrible to me. In my opinion they are hard and brittle (some people love these amps). You can take the same 50 watt marshall and change out the power trans for one that puts 360vdc on the plates and you have a totally different animal - totally different. You can change caps and resisters all day and not make this kind of difference. Even the difference between a plexi output trans (around 3300) versus a jtm45 output (6600 - if my memory serves me) doesn't make as big of a difference though it makes more difference than most cap or resister tolerances. There are a few really critical caps that make a real difference. The caps used in the bright channel are crucial, and changing the slope resister in the tone stack makes some difference especially when you change the treble cap; ie the 250pf/56k vs 500pf/33k. I would be interested to know what the plate voltages of cliff's broken marshall are and what the old amp vdc's are. I'll bet that the old amp has less overall plate voltage, breaks up smoother and earlier, and is simply "browner". If it happens to be a 50 watt amp, I'll bet the the plate vdc less than 420. That seems to be the max before they start getting brittle sounding - in my humble opinion.
 
Transformers and supply voltage. Those old transformers have paper separators which increases the leakage inductance. Normally leakage inductance is undesirable but in tube amps it does cool things.

My old Plexi is running 416 on the plates. My reissue was around 420 IIRC. IMO, the difference is the OT. The reissue has (had) a Dagnall. I believe Alan is replacing that with an MCI.
 
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