Ossie, on behalf of myself and a bunch of other small independent amp builders.... THANK YOU for taking the time to fully document this most important historical amp! Have also enjoyed your explaining other builds you have made, you are skilled and take great pride in what you do. much appreciate these you tube clips, my friend
Ossie, in my experience a lot of the amp builders are not very nice when it comes to sharing circuit tips or to explain the secret sauce of a coveted circuit. I've been building/modding for around 10 years and I've had to work very hard for my experience, teachers like you make this community worth while and extremely interesting! I get that most builders don't want to share the information because it's their bread and butter but amp building isn't rocket science and the knowledge should be shared IMHO. Again, thank you for all the knowledge you provided in this video. Makes me want to be a long time customer of yours amps. Well done sir!
Most of the people who first thought of these designs were probably robbed, an example is Fender....robbed by Marshall. I put my first pre-phase-inverter master volume in a Princeton Amp in 1972, but I don't claim to have invented it! It just seemed logical from the schematic. If you want to do something, create it. That's what your brain is for.
Amazing amp I grew up loving the sound of Jose’s modded Marshall’s. Your amp is the first I’ve seen with the red cap for a 1979. Most amps I’ve seen with the tan and red caps were all 1980s. I heard a 1980 slp I loved and it had the same caps as this amp but with a mustard 2n2 in the preamp. Marshall used different caps until 80. In 81 the used all red caps so you may have one of the first 79s to use red jcm caps.
Ossie, I believe Jose “borrowed” his master/clipping idea from second generation distortion stompboxes like the MXR Dist+ and DOD250 that we’re popular around the time he started first incorporating this mod in the 70’s. Even the build out value of 10k to allow the driving stage a suitable load when the diodes/Zeners conduct was copied. What many don’t realize though, even possibly Jose, is that the 10k+cap combo was just as important to this mod and distortion generation as the clippers were. while it’s a light load for most opamps in the aforementioned circuits to drive, is hard for a 12ax7 follower to drive, let alone one that is overdriven and can no longer maintain a low(ish) output impedance as it is pushed into overdrive, as is typical in most of these cascaded multi stage circuits.
Ossie, Not so much in comparison to the feedback loop circuits like the ts9 or sd-1 etc.. which have a slightly different mechanism but comparable to the straight from output shunt circuits like the 250 and dist +. One thing you will notice is that even with the clipping network in the “off” position, you will still have a noticeable heavier clipping effect (frequency dependent) than if you simply removed the whole network entirely or at the very least lifted its ground connection via the diodes. That’s the loading effect I mention. It’s greatly overlooked by nearly everyone in recent years who has copied this circuit. Also I noticed it logged me in under my google account name this time, but I’m indeed the same person who commented above LOL!
Hey Ossie, I'm so jealous that you have one of Jose's amps, I met him in 1981 when I was taking guitar lessons at this little music store down the street from my house in Chatsworth Ca. I came in to take my guitar lesson from Zac my teacher and I saw about 24 Marshall heads and about 12 Ampeg bass heads, and I asked Zac who they belong to and he said they were Van Halen's ,and that Jose was working on them in the back of the music store, he told me to go back there and meet Jose, and I said Hell Ya!!!! so I went back there and talked to Jose for about and Hour, Van Halen had Just released ' Women and children first' and getting ready to tour so thats why he was working on them, any way I asked him if he could Mode a Marshall 100 watt for me and he said he would, but he couldn't mode it exactly like Ed's cause he was under contract with Ed.. Oh!! by the way yes he had is shop in 'Van Nuy's but so many guitar players wanted there amps moddeed that he worked out of this music store about 5 miles away. Dont Ever get rid of that amp Ossie!!! It's worth more than GOLD!! made by the amp God!!! An thank you so much for sharing all this information of the amp and the Load Box the real secret.
I have a ‘69 plexi jose MV mod as well works and sounds great! Thanks for the video PS Please turn off the music on your next video, your mic level is affected by the music in the background. It’s difficult on the ears Thank you
I have a question about how the input jacks are wired but first I'd like to thank you for creating such a thoroughly detailed examination of the Jose Mod instead of ripping off the circuit and calling it your own👍 What I am wondering is if the output of the added stage's gain control/68k-68k divider goes through the shorted/unplugged stock channel input jacks or are those input jacks resistivity coupled/in parallel with the added gain-stage's signal path?
Agreed. Thanks soo much for putting this together as Jose's do not come up for sale. One of the questions I was going to ask was what Zener, but I see you corrected that below and the actual values are 1N4450.
Not sure if Ossie still has the amp, access to it, or could just trial it by applying a 1V P-P audio wave to the input. Have Gain on "10" and Master on "0". Measure input and output pins 3 and 2. Input I'm guessing will be around 100V. Output will determine the clamping voltage.
NTE Cross reference for the 1N4450 is NTE177. - 1978 Fairchild Book - bitsavers.trailing-edge.com/components/fairchild/_dataBooks/1978_Fairchild_Diode_Data_Book.pdf
Hello, very very interesting video, congratulations! Can I ask you if you have published or if there is a link or if you could pass me the entire schematics of Jose mod's? Thanks a lot!
Ossie, what kind of push pulls are those two pots with the switches at a 90° angle off the end of the shaft? I've seen old stackpole pots with a slider off/on switch, but these are weird. I'm guessing you can't find them new these days.
Hello Ossie, I have to re-watch this But I should mention that in the phase inverter references to the resistors......as best as I can SEE on my computer screen what you reference as a 2.7K resistor is a yellow band and thus a 470 ohm traditional resistor in that position. I would suggest measuring it...as I could be wrong or you could be mistaken.......doesn't make sense. I was waiting for the zener diode aspect.....and I'm glad you pointed it out. I use diode for clipping the wave form in other aspects of a pre-amp circuitry which is not this particular type with the cathode follower. I would also point out, but without referencing the schematic, the 500K master pot is not the specified 1 meg type......so sort of in effect in the normal mode the reference signal is technically only halfway separated to ground than being 1 meg isolated from ground and thus some of the signal is still going to ground and not reaching the phase inverter. Jose may have chose the pot value based on what he had on hand, or it may be that the extra gain stage in front when engaged to push the signal might be too much without having an attenuating resistor inserted. BUT without the extra gain stage engaged to push the signal UP....its going to not let the base signal reach maximum potential to drive the phase inverter.......in its natural configuration. WHICH could be like saying why install a turbo or a blower on your cars motor....if you never intend to utilize it....RIGHT. There is one defect with the Jose extra gain stage up in front, which concerns phase....since every tube stage inverts phase. Laney corrected this in some of their amplifiers by using both sides of the extra gain stage being put in front of the pre-amp. Jose left the second side of the tube not being utilized. They should technically be both cascaded into each other to correct the phase when egaged...and the gain adjusted by the typical means. You have the phase of the strummed guitar......feeding into the amp and ultimately coming out of the speakers.....which technically should be in the same phase relationship which would be MORE MAGICAL when you understand.......LOUD IS LOUD.....so LOUD might be defeating.......but my take on the matter is that the phase should be minded and correct. The Beauty of the circuitry being the clone of a Tweed Fender is because of the cathode follower and its effect on the signal. The tone stack is tuned to a particular point response, and the treble cap is adjusted to more of the mid frequency's as opposed to the high end......I oftern use a .0015 cap in place of the 250pf to 500pf trebele cap to back off the high range to be more useful for guitar, but my point is....the tone stack is still a high loss type tone stack.
Essentially what JOSE did, when you take into the account the ERA....was to keep the bridging of the 2 channels intact which can thicken up the tone with the 2 pre-amp signals hitting the power tubes as opposed to one in the traditional sense. BUT the added gain stage was just adding the Marshall one wire MOD to the amp with adding the tube for it rather than pirating the second channel as was the case when doing the 1 wire MOD..., SO JOSE kept the best of both worlds.... Then JOSE had the mind to add the diode clipping and where to insert it into the traditional circuitry.....to push it ONE MORE step. Though there are a couple areas where things could be pushed a bit more. Seems JOSE was not a fan of drilling holes in a chassis to add switches or extra pot controls back in the day......which has me scratching my head and the state of doing any tweaking and MODS in that era......the amps had not achieved the super collectable status as of yet then......at best they might have been a 10 year old used amplifier on the market of used gear......whether you could afford buying NEW or if the players budget was limited to acquiring cheaper used gear as tools of the trade.
When you state that the extra gain stage is a direct to the grid....from the input jack with no resistor in series....., is there the 1 meg to ground resistor in there for the grid (grid leak) ? The series resistor is really not needed other than to block high frequency as for picking up radio transmissions...with minor attenuating aspects for the input signal
@@ossieahsen6732 Thanks! It's on the bench again, because a power tube socked sparked :( Waiting for the new sockets rn. I hope the 6550 somehow survived.
So the Line Out is right off of the speaker jack, but it is labeled "Preamp Out". Technically this is after the power amp (not right after the preamp). That is REALLY useful if you send that signal point to another power amp and cab since now you can drive the power tubes hard and get their distortion goodness. Very simple and cool. May have to try this... Thanks again!
@@gerritkolthof2773 if it will be carrying the guitar signal, then yes, you will need shielded wire, but not is its carrying DC. Shielding is more important the closer to the input you get.
Ossie excellent walkthrough, you clearly know what's up and it's nice to see someone actually document this stuff openly and accurately (those who undertake a build like this know you need to see the source for yourself) rather than letting Jose's great achievements get inevitably lost in history due to keeping it "in the know". I have a question regarding the input resistors to ground for the lead/Bright/Normal channels, are they all 1M? So when jumpering is active you get a voltage divider using two 68Ks into the grids of V1? What is the purpose and value of the ceramic disk across surrogate plate to cathode? Thanks!
@@ossieahsen6732Are one of the MV's blue coax cables connected to the V2B 100K cathode R under the board? Is that where he made that connection? Do you think a 1M for the push-pull master would work better for less load or would that result in some undesirable brightness?
This is awesome, thank you for going through the whole circuit in detail! (I must admit I'm curious who's amp this was though haha. I'm guessing it belonged to one of the 3 Monkeys--the obvious one)
Thank you for taking the time to make this outstanding video. Do you get any volume loss when you engage the Zener diodes? I played a Cameron Atomica that supposedly had the Zener mod, and there was a slight volume drop, and slight roll off on the highs (when engaged)..
MightyMikeamps... Thanks for watching! You are welcome fo the vid :) You do get a volume drop when you add a zener network for sure. But..... If you watch the vid closely you will find the zeners are never out of the circuit regardless of the push pull pot. The additional volume drop on this amp when the pot is in pull mode is due to the insertion of that lower deck of the dual pot in between the cathode follower and the tone stack. This also has the effect of cutting off some high end. Hope that helps!!! Ossie
so the zeners are only engaged with the MV pulled? (pre-TS master). Pushed, the zeners are not in use? Any option here to disable the zener in pre-TS master mode (pulled MV)?
Great Video Ossie. I was just rewatching it after months. i noticed that the first 2 B+ droppers after the choke are not 2.7k and 10k, the big brown carbon comp one looks like a 4.7k, so it's still less than 8.2K+10k, so are the voltages a little higher? And what's the deal with the bias feed resistors being 180k ? Maybe it was an amp originally made for 6550 tubes and that explains the bias mod?
Fantastic video, thanks so much for sharing this. Curious to know, if you have a preference on a plexi cascade, as the signal leaves the vol pot, would you use the stock 470K (mixing) resistor, or would you set up as a voltage divider before dumping into the next channel?
@@ossieahsen6732 Thanks, I have tried 470k/470k to ground, it was not enough. Will keep going. Curious to know if you recall how Angus's was set up. Nonetheless, I will play with it and see where. Thanks again, I look forward to more videos!
I don’t see a part 2 video one discussing the added pre amp tube and it push pull double pot . Is there any way I can email you and get some information more on this amp or maybe a layout or a still picture I’m just getting into building amps and this is absolutely great thank you so much for doing a video like this thank you Ossie
If your output transformer is stock, why is it missing the adapter brackets that were always installed from the factory? I suspect that output transformer was replaced with a new one but of the correct type.
It's impossible to tell as there's no sound demo...however the preamp circuit path as described has a rediculous amount of treble peaking and lots of bass-cutting. Then there's the rain-barrel 600uf mains filters - is that perhaps where it would be of benefit to re-inteoduce bass into the circuit? Because there's zero chance of the amp not having enough voltage and it either packs a wallop on the low end or it is right, tight, tight
Hello, I believe I see wiring going to the ground of the output jack through a resistor in brown heat shrink. Where is that going, or what did you find it was accomplishing? That wire or wires and resistor run between the output ohms selector and output jack. Is the NFB purple wire going to the 4 ohm OT tap / yellow wire?
@@ossieahsen6732 The NFB is going to the selector, but I can't see which pole / tap it goes to. The wire and resistor covered with brown heat shrink sits between the speaker ohms selector and output jack next to it. It appears to go to the ground buss of that output jack. I don't think it goes to the line out. Curious.
@@anondusery1271 I don't have the amp open and in front of me but I can say with great certainty, having owners this amp for almost 20 years and having built many clones of it that there is noting unusual there at all... I think you may be seeing the insulation on the ground leg of the OT secondary,,,, This OT has rather heavy knitted insulation that is somewhat unique looking. The feedback tap has been moved around I bit over the years (by me). It sits on the 8 ohm tap now I think. Hope that clears it up for you Ossie
Hi, fist of all thank you very much for sharing with precious information! I have a question for you: as the 10k to .22uF cap to zener diodes path is permanently linked to the signal (coming out of the cathode follower (and from the diodes to ground), doesn't this affect the circuit even when you're in "pulled master mode"? Or the 10k resistor is sufficient to exclude the action of the diodes to the guitar signal?
Shredgd5, The 10k is what is often referred to a compliance resistor. It helps set the threshold for the zener so to speak.... its also ALWAYS in the circuit! Hope that helps! Ossie
Thank you, but I know and I didn't mean that. I meant that when you're in pulled mode the zeners are not totally excluded, because there's a tap from signal to ground through the 10k/.22uf/zeners (the same you see in the schematic of the BE100, actually)
Did Jose ever cascade the additional tube into both sides of V1? It seems that he added a tube with an on/off and a .68/2k7 into V1b where you can just cascade and change the values of V1a into V1b. Besides adding an additional 100k to the plate resistor its the same thing, isnt it? And is that push/pull controlling gain as well? You would never jump the channels AND use the jose added channel, would you? And if you did, its still not a cascaded V1b to V1a. I assume this wouldnt sound that good.
I don't think he did that... but anything is possible I suppose. When its your amp I suppose you can jump it .. its up the the end user what sounds good :) Ossie
Great video!!! One question: what is the purpose of moving the master volume and the clipping diodes before the tone stack (as opposed to just leaving it after)? Is it to implement it where the amplitude is higher (I.e., before the loss of the tone stack)? Or is it so the EQing can be done on the fully distorted (post-diode-clipping) signal rather than before?
Hi Jasco ! I think you have answered your own question!! The diodes def work better in this position as there is more to work with before the tone stack losses. I also think the EQ works a bt better this way. Also If you watch carefully you will see that the master volume is actually a dual selectable one that can sit either before or after the tone stack depending on the. position of the push pull. Thanks for watching!! Ossie
Hey Ossie, watched the video. What is the value of the first valve stage, ceramic cap to ground, 1000 or 2200 pf? Also could not find specs on either of those zener numbers. Are they 24v zeners?
Hi, Replicant Audio! The value of that ceramic to gnd is 0.002 or 2200pf The zener number is my bad- I was reading it off the parts box while doing the narration off the top of my head and transposed the stock number for the actual zener type. Should have been obvious at the time -- since when does a zener designation start with an "a". LOL The proper number is 1n4450- Sorry about that !
@@replicantaudio5810 I do not have a data sheet for the part, I am sorry to say. The part number I gave is as it appears on the part- Hope than helps: Thanks!
@@JohnLysonmusic Hi John :) Thanks for the question, I think a 1n914 would do the trick for you :) I drew out the Jose master circuit on a peice of paper somewhere in the vid.... But, If Im hearing your question correctly the red wire goes from the lower 500k pot wiper to the dpdt switch top right lug. I think the drawing shows the correctly. Hope that helps :) Ossie
at 15:39...it looks pretty clearly to me as 470 ohms, which of course is standard as the common cathode resistor of the phase inverter. Of course I'm referring to this model Marshall. Am I missing something???
Great analysis! As car as i understand Jose was trying to reproduce the symetrical cliping of the phase inverter stage before the master volume. Is that right? In your opinion is this succesfull?
Phil, The clipping is symmetrical, yes... I have not scoped out the PI to determine if the clipping is the same as would occur in the PI under max signal.... My guess is its not exactly the same Hope that helps Ossie
Like the vid. Good history. Curious of what tour and stages it’s been played. Unless you’re from CA, you may not know how it’s pronounced. Van NEYES (guys) 4463 A Van Nuys Blvd.
ossie, this was amazing, my questions kind of random but could the mvc push pull mod be added to a mesa boogie royal atlantic head? thank you and new subscriber
Nixon, Thank you for watching and thanks for the kind words! I don't have a schematic for the Mesa you mentioned but it is possible that it might work.. its also possible that the architecture of that amp wound tended the mod redundant or be incompatible with the circuit :) Ossie
It all sounded like a really 😅 good interesting tour around a hose mod amp. I would have loved to have watched to the end only I couldn't because of the background noise. Can't understand why you're trying to impress a classical element on something that has point blank rejected it, a bit like going into a book shop. You'll be hearing it till it hurts. Best Regards . Don't stray from the path of righteous Tone.😊
Ossie -- Van Nuys is a Dutch name, pronounced "Van Nyze" . If you ain't from around here and haven't heard it spoken, it can be hard to guess how to say it.
If you watch all the vids you will find how the inputs relate / work with each other... But simple answer is yes -if you are in the lead input and the extra tube is activated by the PP.
Hey ossie love the video thank you for it. I have 2 questions. First does the dual master pot being 500k make a difference than the normal rating of 1 meg for a volume , and where can i get that type of pot. Will the bourns dual gang 500k push pull pot work the same.
@@ossieahsen6732 Guys I have a JMP 1980 that has those huge capacitors also, but don't know who build, I got it used, I bought years ago because it had push/pull and added stuff didn't even try it, but it sounds phenomenal, is probably my favorite amp, I would like to know what mod, and who build I just found your channel and watch the entire video about this jose mod. Thanks for all the info, Great to still have people that take time and pass knowledge to everyone.
TeleCustom72, Thanks for watching! I have not drawn one up... I pretty much know it by heart :). Somebody probably has by now though! All the best Ossie
1: Output tube cathodes are in parallel. Not series. 2: With the gain knob grounding the added triode's plate, how does this bypass the gain stage? Is it a mute switch?
Lazzer408 Thank you for watching! 1-Yes the cathodes are in parallel... hard to talk and think at the same time :). Words will get mangled! 2-The plate is not grounded... the capacitor after the plate is grounded. This mutes the stage. Grounding the plate of the tube would not be a good idea :) All the best Ossie
@@lazzer408 No problem. Happy to help. Just wanted to make sure that its understood that the capacitor is grounded and not either pins 1or 6 of the ECC83. Good luck with the mod! Ossie
@@lazzer408 The Switch is grounding the capacitor off the first added gain stage. Nothing more than that. I don't even know why someone would need that to tell you the truth :) Its just a mute switch.
Hey Ossie, got a quick question for you or anyone reading this with current knowledge of these heads,....my question is: what would one of these "late" 1960's maybe early 70's "Plexiglas" 100w super lead modified by Jose cost? Thanks in advance.
@@rmaubert4754 RM, I think if I had to sell this amp I would probably put it on Reverb.... I have no idea what I would list it at :) If you are trying to find one to buy I think it would be difficult at best. Ossie
Just curious: Why won't you say who the amp belonged to? Is there a reason that can't be revealed? It's not like it's a matter of national security or some sort of government top secret. So what if it's EVH or even JC himself? Who gets hurt and why? I just don't see how there could be ANY harm in it.
Hey Ossie thanks again. Need some clarification on a couple things... 1. Mixer resistors - usually 220k and 220k. You suggested both were 82k, but bands dont appears to support that and look like (gray, yellow, silver)?? PLEASE CONFIRM. 2. Dropping resistors - You made a couple err's in both PI (470R stating 2k7) and also dropping resistors. I think you have a 2k7 fetish!!! lol The top is definitely a 4.7k which would increase the voltage. You suggested the bottom was 10k...but again, bands dont support that! It looks something like brown/green/yellow or something, which would be like 150k!! What is the bottom dropping resistor value and if known, what is the voltage to the PI?? PLEASE CONFIRM. 3. NFB tap - You communicated the FB resistor to be a 100k, but never stated what tap Jose use! Is it 4 ohm, something else? PLEASE CONFIRM. 4. Bias circuit - there was changes including 2 stacked resistors, but you made no reference to any of the values other than the 2 10uF 160V caps. PLEASE CONFIRM. Thanks in advance!
Thank you for pointing all my mistakes out :). Try talking off the top of your head for an hour and reading these parts with 50 year old eyes lol. Anyway Ill do what I can to help out- I loaned the amp out last week so I don't have access to it : but... 1- Looks like 180 k from the vid- my bad 2- I cant really see that metal film too well in the vid- but it looks like brown black orange to me- 10k. My memory of the amp is that its def not a 150k- the b+ voltages were pretty normal 3- The NFB is taken off the impedance selector and varies with the switch position- pretty common 4- The resistors there aren't that important as they are just there to allow for the biasing of real 6ca7 power tubes- The amp probably ran too cold without the change... Hope that helps and thanks!
@@ossieahsen6732 understood. thought you did a great job and almost like it was scripted actually....very smooth. mistakes can happen when youre under the gun n excited soo understood. thanks for claring things up. i was wondering of Jose put the NFB on the selector output or independent tap. i know the bias isnt all that important just adjuat for the range you need. im just anal and a stickler for detail. i did see on another angle it did look like brown black orange and the second dropping resistor 10k. he did lower the one to 4.7k soo would be looking for higher B+ downstream and that 180k if there is indeed a brown band means he changed this from 220k's to 180k's n not hit the PI as hard!! Good information. Thanks again!
@@RozsaAmplificationLLC No worries! Thanks for helping out! Sometimes text can convey unintended emotion- I was being funny to be sure- and I do appreciate you finding the errors- Its tough for me not to make mistakes while on camera- I don't know how people do it for a living so well :) But getting it correct is important so the corrections are very helpful the end goal! I have seen 180 K resistors as the bias splitters in other amps- stock ones so they may be stock. All the best Ossie
@@ossieahsen6732 Yeah, I got a good still of the bias circuit and 2 resistors stacked. It's a 100k on top of 47k soo net 33k-ish value. I would double-check the tap used...facing the back of the amp, the NFB wire looks to go to the right terming and possibly yellow wire on it. If so, that arrangement....100k on 4 ohm tap is very common Marshall value. Usually 100k on 4 ohm, 56k ish on 8 ohm and 33k on 16 ohm. As one goes up, the other goes down. The impedance jack appears to have a back wire that is the output to the speaker jacks. The purple NFB wire does not appear to be going to it. If applicable, confirm. Thanks.
@@truescotsman4103 Never heard Randy used a José modded Marshall. He had a white Marshall that was built for him at the Marshall factory. Only mod on it was that if you used the normal Channel inputs the channels were cascaded so you got more gain. But on pics i’ve seen Randy uses the high sensitivity treble channel input. He used his MXR Distortion+ a lot i think.
Your T-Shirt says "solderless"... so, how can you work on an amp? On the other hand, that amp looks a little bit weird. With all those wires flying everywhere, you're good to pick up radio stations rather than expect to play guitar someday. With all the modifications that have been done, they even haven't replaced those cheap and nasty 1N4007 rectifier diodes with some FREDs or something... what a shame!
Why did you remove the MARSHALL logo? Only dudes in punk bands who are embarrassed to be seen playing a "heavy metal" amp rip the logo off or cover it with electrical tape. 🙄
