Restoring a '83 JCM800 50w 1987 'Plexi'. RESTORATION, BROWN SOUNDS & CIRCUIT TWEAKS!!
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- Опубліковано 27 лип 2024
- I picked up this 1983 year model 50w 'plexi' for the personal collection. It's taken some work to bring it back to full working order. This clip covers the restoration, voltages, before and after tones and some Variac fed EVH brown sounds to boot. I finish off with analysis of the tweaks I made to this 50w Plexi along with voltage readings and power output with and without the Variac.
0:00 Variac tones with micropitch detune
0:54 First look at the new purchase
2:24 Condition report
7:49 First tones
11:04 Summary of 'fixes'
12:17 Tone test - 'restored' amp
21:51 EVH Brown Sound
26:05 Variac'd amp - my thoughts
28:53 Schematic walkthrough
36:06 Voltages and Output Power
headfirstamplification.com
great info, thanks for the free lesson, variac now moved to the top of the shopping list.
That Destroyer is beautiful!
I have a Fargen Custom Shop Bass Plexi that is such a joy . Every guitar keeps it unique tone. And every nuance of your playing comes through. No where to hide when playing it
They are unforgiving beasts!
Jayson, I know you think it sounds good. I can appreciate your talent. You do get that EVH tone. I like a 1M NFB to the 8 ohm and a 200mfd for more punch on initial filter cap and 0.1mfd on preamp to power amp coupling caps, a 25mfd bypass cap on the 820 cathode V2. Especially important is a treble cap of 560pf for the tone stack to let in more mids. On the JCM 800, I like a 1M grid stopper instead of the 470K. I like some wooley on the lows.
Killer sounding amp. Going to get off my duff and finish building an old plexi style amp that I have been working on for quite a few years - I have too many project amps. Much appreciate the rundown on this amp, with your changes, and the excellent discussion about how the changes affect the sound. Thanks!
wow you really nailed the eddie tone with the variac . i think the secret is re-biasing the amp at the lower voltage. that was never discussed over the years
Great video and great tones! ⚡️
Again, awsome EVH tones Jason... Killer sounding amp.
Yep, that's my kinda amp! Very cool mate, great tones and insight given the circuit I'm putting together atm. That's a keeper. Cheers Jas.
Love it!!! Makes me miss my JCM 800 2204 I bought new in 85. The JCM 800 line were screamers.
Amazing passion piece Jason. Loving it.
Thank you kindly!
Mr Brown Sound does' it again:-) My first Amp i put "fingers on" was a 2203. learend a lot, but would'n do it these days anymore:-) Top Sound and work. Greetings from Switzerland
Sounded excellent with the voltage reduction 👌👌
Sounds fantasic, great to hear this Amp in the zone, loving the variac sound. Jason you are a talented player and tone tweaker. Thanks for sharing.
Thanks Paul!
Another great video. Thanks a lot.
Glad you enjoyed it
awesome brown sound ! killer !
Cheers!
These low watt modern plexis sound great for rehearsal, gigs, etc... I have one and put all controls on 1PM. You're good to go, no pedals needed!
What low watt modern plexi are you talking about? The amp in the video is a 41 year old 50 watter.
@@humbucker1414 i consider these low watt (50watts as compared to 100watts) and JCM 800 series a "modern" equivalent to the JMP and JTM series(altough they have a different tone character)
@@pittbrat7963 Fair enough, carry on. And you're right they sound great!
I had an 1983 JCM 800 “Plexi’ I sold to Music Go Round in Minneapolis about 3-4 months ago.
I live in the Twin Cities. Which Music Go Round? I believe there's more than one in Mpls. Probably gone by now though.
@@willdenham Burnsville store…….ya it probably went out the door right after because I have been there many times since and never saw her!!!!
Another great episode!
I would be interested to know why that style of MV is no good in a plexi but IS good in 2204?
Because the 2204 has 3 gain stages and the cathode follower, where's a 1959 or 1987 only has 2 gain stages then the CF. A Plexi relies on distorting the phase inverter tube to get it's gain, so if you put a master in front of the phase inverter in a Plexi you are starving it of the fire it needs to cook!
I think the superlead and 2203/4 or a simple modded version of either are my favorite amps of all. I really dug what you did with the be to Jose video, I’d like to do something similar but the relays are a bit over my head for now. Currently got an 800 that I’m modding similarly to the blue channel on that amp.
They are the best circuits!
Nice info
Instant rock and roll damnation !
I recently acquired a 1983 Marshall jcm800 super bass 100w. It has 5 black unbranded filter cap cans. The board isnt ST1, but everything looks original. Planning to rebuild it to a Lead series with jake e lee mod and etc.
Awesome, I'd love to see how you get on with it
The world needs more people like you, thank you to bring us this videos, this channel diserves more followers. Abrazo grande desde Argentina 🤘
Wow, thank you
Killer video
Thanks brother
I hoping to get tones like this from my/ your jose/cali build! Looking forward to a video on which transformers you prefer in your builds and what you use for 25,50 and 100 watt versions. thank you in advance!! the original filter caps in my (83-84?)marshall were blue LCRs
Would love to see your take on the #36 mod ... or how to do the Marshall AFD preamp circuit to a 2203/ 2204 !!
this will happen! And the #34 too
So... your 4X12 was in the other room? :) Thats pretty much volume all the way up because the difference in volume is not so audible after 1 or 2 pm lol. Interesting vid and tweaks(not mods!) sounds a bit different from the "stock" model
Nice! New guitars? EVH and the Explorer!?! Killer tone and playing!
Had them both for a while now David, 2 or 3 years at l'd say. The Explorer has been featured a few times, but this was the first for the EVH.
@@HeadfirstAmps 1 out 2 is not bad for me (EVH's debut). Killer tone and playing!
Yep…. That is THE tone.
sounds amazing!
i have 76' 1987 that i would like to do some tweaking to. this seems to be right up my alley, as i like the late 60s sounds. but i also like the AFD sounds haha, im torn
Choices choices!
@@HeadfirstAmps is it possible to wire it to 60s specs, and then add like a hot mod to give it an AFD tone?
Sure. I've done a few previous clips showing the #34 & #36 mod.
@@HeadfirstAmps its interesting, looking at my amp, in the R1 position its a 10k, which is the spec for the MV model. but mine is a NMV. i wonder why that was changed.
Great sounding amp. Sounds like a great old Marshall to me. Scorpions Blackout tones and other classics of the era. I am not hearing Van Halen tones from it though. Early VH is VERY specific. 1968 Plexi Spec, 50k Mid Pot, 330 Fat Cap, 6CA7s, old Greenbacks. If you don't do it EXACT... you won't get the early EVH tone.
...and that the actual tone was Ed himself.
Trouble is you really can't hear the nuances when a superlead is at volume.
Does this cause the oxidizing inside the powertubes when you lower the voltage singificantly?
Sounds great! What delay/reverb are you using and is that in a passive or active effects loop? Thanks
Back in this clip - probably my Lexicon PCM80. I can't remember exactly.
3:38 If it was for the master volume(or some other pot), it may have been a long shaft pot and they attached the pot onto the bracket at the right distance so that only enough of the shaft protrudes outside the chassis to fit on a knob rather than have the knob on the end of a long shaft sticking way outside the chassis
EDIT: Man, you nailed that brown sound :D
Looks like that doesn’t it!
@@HeadfirstAmps Honestly, one of the things I love about digging around in either amps in for repair or amps that I've bought and inevitably modify like I do with literally every other piece of electrical goods I get is amp archaeology if they're not brand new amps. Trying to uncover a story about what went on inside and what was done and why it was done etc etc
Then there are amps like a particular JCM2000 I had in that suffered thermal runaway due to the factory issue ( was a 97 amp)...owner wanted it repaired. Opened it to find someone else who didn't really know what they're doing tried everything to fix it without knowing seemingly what the issue was. There were tracks and pads ripped up everywhere, terrible attempts to fix the damage, godawful solder work all over the place. They made it much more work to repair...much, much more work. Took a while and required some creativity but that amp is still going strong years later.
Those black Filter Caps had been used on 800s in 81-83 timeframe, I pulled a few of those from amps which had been for sure untouched. Maybe they covered a shortage on LCRs?
I think you’re right. As far as I can tell all the caps were original, which is a strange mix!
Sounds great Jason, did you use a booster for some parts? It's got load of gain, right?
Thanks. No booster, this is straight into the amp.
Is it possible to mod the SC20 to this spec?
Man,that thing sounds amazing with the Variac…..it absolutely nails that sound…nobody can play like him,but that’s the tone….are you using the FX in the AxeFXIII??…
Yep. Flanger for Unchanged out front of the amp, that's it. AXE also used for IR, micropitch detune and plate reverb. A little panned delay from the PCM80.
@@HeadfirstAmps that just sounds killer….I have an AxeFXIII as well…I love that thing…I use it like you do…in fact,I copied your patch when you did the Jose comparison with the real amp….Switching back and forth between the real amp and the model is great….I have to dial in some of these EVH FX…your playing is great too…love these videos..
Sounds great. How do you like the EVH guitar?
It's great now, really nice. But it did need some setting up. I don't know whether that was a result of the first owner, or whether it came that way from the factory but I needed to shim the neck to allow the Floyd to be decked.
Doesn't the lower wall voltage also lower the heater voltage too? Did you test your 6.3v after the change? I'm just curious...
Timely vid, I'm right with you, I finished my own version of a 2204 this morning, tube rectified, I used a JTM 45 power tranny, a few tweaks here and there, and a twin pot lar-mar type ppimv, and man, I'm in amp heaven again, haven't had one of these for the last decade or so , it feels like home, (and half my pedals suddenly became redundant! ) ;).
It sure does, the heater voltage was running at 25% less.
@@HeadfirstAmps Yikes! 15% lower than recommended lowest. I get the same "Brown" effect with my own "2204", but with friendlier heater spec voltages, by running a 5u4GB rectifier, 32uF reservoir cap, (22uF for the rest,) and a 47K Cathode Follower cathode resistor, I love it. With a SS/tube rect switch and cathode R switch, (3pdt could do both at once) it could be switchable, Brown/Stock, but after playing it like this I decided I don't need that option. Cheers.
@@HeadfirstAmps According to tube life expectancy vs filament voltage data, that equates to less than 3 hrs... would be a fun 3 hrs tho! ;)
Awesome tone, post captures on quad cortex?
Yes, I'll be doing that! Someone else asked too. Username is 'burger'
Sick , can’t wait , your captures are some of the best 🔥
You're not a fan of the higher-value bright caps? I read somewhere that the EVh Marshall has a 0.68uf on the presence control instead of a 0.1uf.
I love all the brights. I’ve got a 4n7 in my ‘69 plexi. 0.1uF presence I believe
LCR caps are originals Jase.
Hey, has this JCM800 Super Lead been modified for more gain or has it just been restored to stock respecting the stock component voltages?
This Marshall is probably the best sounding Marshall ever and I would just like to know if it is stock or has it been modded?
Thank you very much.
Not modified. But restored to a ‘68 spec 50w 1987.
@@HeadfirstAmps And do you have any rear FX Loop installed for that reverb tone from the rack or is it all from the Input?
Thank you so much for that great tone.
question, on V2A, the .68 cap over the 820r.. did you add the 330uf cap to the .68, or replace the .68 witht the 330uf?
Add it on top, that's the way its done in the SL68 which is based on Ed's plexi.
@@HeadfirstAmps thanks!
@@HeadfirstAmps escuse me , from italy, about (680 +330) so you choose near 1000uf on .820 ?? Is this the second in series? And if this is right are you speaking about series (v1 to v2 master model circuit or v1A and v1B parallel on v2 tone like a old plexi 4 input with bridge exterenal jack? ( sorry for the stupid question but I didn't understand if the pre part works in cascade-series or v1A v1B in parallel like the plexi) mixed to v2 tone tube. thx a lot, your video it's really fantastic .
The two diodes straped in on the ground could be an attempt to quiet the noise floor?????
Perhaps! Look up 'coring circuit' to see how that is done properly.
@@HeadfirstAmps I've seen it on the grounding side of heater pins actually. Maybe the guy who modded ut thought ,,,,why not,,, the parts are cheap!
The most importanr thing is to get it to stock first then proceed from there! Other wise you end up chasing your tail!
Those pickups on the Suhr are kinda mushy. I think they are Alnico 4? I know they are not Alnico 5.
I have a variac I bought of eBay years ago….are all variacs created equal?…in other words how do I know if will handle my 100 watt amp?
Scott. It will have a max current rating and will be fused. What's its rating?
@@HeadfirstAmps it says input 110V Output 0-130 V 500VA….it has a 5 amp fuse…it says Max 500VA…
You'll be fine with that. Your 100w amp probably has a 3 amp mains fuse, so it will blow before your Variac reaches maximum current.
@@HeadfirstAmps Thanks Jason!!….I didn’t want to blow anything up..
I’m thinking about getting a 1982 JCM 800 2x12 combo, what type of mods would you recommend, if any? If you have an email I could send you some sound clips I got from the current owner……..Thanks!!!!
You can do the JEL mod to this, I have a prior video on how to do it.
I might have missed it...but you could have at least given credit to the people that released Ed's actual amp design 100% (me and Dave Friedman), geesh!!! lol
....and don't forget the 6CA7's...part of the "magic"!!
Lol Robb, yep!! Your thread on sloclone was a big help!!!
@@HeadfirstAmps lol. thanks Jason and lovin' all of the videos my friend!! :)
After Dave gave me the real design, I twisted up a 6CA7 50-watt version. I have a steel chassis an utilized the 100V and 240V "trick" Mark Cameron communicated to me, thereby utilizing and internal "virtual variac" which cuts the voltage down to about 84% from 475 plate to about 400V! Sounds killer and had local EVH tribute guitarist out of Detroit to some clips. SPOT ON EHV1!! :)
Thanks again to Dave Friedman for supplying the design 100% so we can all enjoy it and VH Tribute bands can do the songs justice and as close as humanly possible!! :)
@@RozsaAmplificationLLC I'd love to be able to run the PT primaries that way, but here in Australia there is no where to go AC wise! Custom wind PT's me thinks!
Boy am I confused..
I thought a JCM 800 and a plexi were completely different circuits ..
Now I know that a plexi is a non master volume amp and a JCM 800 is a master volume amp..
to see a JCM 800 with a 4 hole front panel is strange to me , Ide never seen that before
I have a JCM 800 50 watt two input , horizontal inputs which I know is less desirable than the vertical input earlier 800’s
I guess my question is is once you add a master volume why do you/they still call it a plexi..? And can I have my master volume JCM 800 50 watt modded to be considered a plexi..?
A JCM 800 is not a Plexi !
You do know JCM800 is a series not a model, right? It’s a ‘Plexi’ circuit mate. 1987 model.
@@HeadfirstAmps Every one of them I ever played had less volume and drive that a 1959 model.
It depends on the year, and the model. The early year JCM800’s were identical inside to the JMP’s that preceded them. By around 85/86 Marshall started to change the 100w amps by screwing with the filtering.
Plexi is being used in inverted commas in this video to describe the circuit, not the plexiglass panel that it obviously doesn’t have.
@@HeadfirstAmps Obviously, they suck Balls !