'76 Marshall 2204 Cascaded Gain Conversion Part Two
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- Опубліковано 28 кві 2020
- Part two, showing the actual changes to the '76 2204 circuit.
More details on this amp and hundreds of others can be seen in my repair galleries at pg/PsionicAu...
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That is an incredibly nice specimen of a 1970s transitional Marshall amp, and I really do love their 50 Watt amps. Yes, the Bulgin connectors are obsolete and often dangerously degraded but, at one time, those were medical grade connectors. Those plug in impedance selectors are quite dodgy too, and I have fought to re-tension both of those sockets and maintain originality. Bulgin makes IDECs now so.... Yeah, the old are obsolete.
Eddy currents mitigation. Brilliant.
Great video! Is there also a video of someome playing this amp?
How can you tell if you have a microphonic cap or resistor?
Trying to find a video comparison of cascades vs non cascaded in a JMP 2204
Are you kidding,,,,,,,,the blah blah makes for the best video.
During the video you mentioned several components that were injecting noise (diodes, caps..)
How do you find the origin of noise?
How do you know what color OT wire is what ohm? I know the "standards" of black, yellow, green on 100w or yellow, green, grey on 50w. But if you are unsure, how can you test?
Thanks for this informative video. But the video title suggested a discussion of the actual cascaded input conversion! Would have been great if you pointed out all the various things that were changed. And was the goal to completely mimic the later '78+ circuit?
Did you watch Part 1?
Splitting the buss ground... If you remove the buss from mid to treble but connect master to mid, isnt that doing the same thing? And where did you ground each side to on the board?
Im trying to wire a 2possision switch on my JTM45 from tube depot that took me a good 28 hours to build im a little slower then your average tube builder ... lol ... but im wanting a really agressive type tone but not brown soundy more keep original tone but much morer gain even though this amp has a PPIVMV it still lacks the gain i want without pushing the power tubes way louder then im looking for ... i hope to do that but im wondering how if i do a cascade or a resiistor or on the switch not sure im doing research . any suggestions/
Cascading a JTM45 isn't as easy as forums lead you to believe. It's not a good platform for high gain - too many things need to change.
My advice is to build it per the Tube Depot instructions. If jumpering the inputs doesn't get you there, use an overdrive/booster pedal. Worked for Clapton.
But at the end of the day, a JTM45 isn't a high gain amp.
I have 1959 plexi 50watt, basically a 1987 but upon seeing the turret board layout, the parts are more akin to the 1959. It already has an effects loop and Post Phase inverter MV. Is it possible to do a switch that makes the MV pre phase inverter? Also, can i cascade it to achieve more gain, kinda like the Jose mod and other modern heavy gain mods but retain the plexi sound on low volumes?
The post phase inverter MV is the better choice in a 1987/1959, and making it switchable to pre-PI would be a very expensive exercise with a bad result IMO.
As to increasing gain, I don't know whether you could. No offense, but I cannot know that. I could, and I could name ten other techs around the country who could. If it makes you feel better, I could name twenty professional techs who could NOT.
But in general, if a jumpered 87/59 Lead doesn't have enough gain, hit it with an overdrive pedal set for low gain but high output. Will run you $75-100, you can turn it off, and you don't have to mod the amp.
Jose added a tube. He cascaded that new tube into v1b. He also allowed you to internally jump the channels but the gain increase on jumping isnt much. Then there are other things for gain but the new tube is the most added.
Do you have any videos of you actually doing the work? I just got a ‘76 JMP 2204 I need to convert to the cascaded gain. I can work a soldering iron. I’ve messed around in amps, but had super easy instructions and help doing so. Do you have any sort of instructions that label it all out, paint by number style?
No, I don't want to get into major soldering instruction because I'd get too many questions on it. I only have so many hours in the day.
I will be doing some basic soldering "how-to's" soon, like bass wiring or making cables. But nothing involving high voltages as found in amps.
On that note, cascading a Marshall is not a good thing to be "messing around" with. So many things can go wrong.
People who want to learn should make cables, then make a lot of pedals, then maybe try a Champ kit build - assuming all the pedals still work six months later.
I'm not being a snob - this is dangerous work, for the person doing the work, for the player, and for the amp itself.
@@PsionicAudio no worries. I understand how to do the work safely etc. I used to have a jcm 800 2203 I modded to #34 specs with some help from a local friend and Frank Levinthrough emails some years ago. Miss that amp, so I eventually hunted down the 2204 JMP I just got. Just learned about the cascaded gain issue with the early ones, and discoverers mine is non cascaded. Wanted to update it first, then possibly work a switchable #34 mod if I can figure out how to do so. Just looking for a thorough idiot proof (as far as idiot proof can get with something like this) instructions on how to do the conversion. You’ve got some awesome in depth videos. Appreciate all that you do.
yea because i thought this was a video showing you how to do it, but turned out to be a bunch of talking and trying to scare you to not do it because you have to be really smart so you probably don't need to do it because you are probably are not smart enough.
What temps are you using when doing this work?
I do most work at 700 F. 750 F for removing unleaded solder. 800 F for large eyelets/turrets (working fast).
@@PsionicAudio Can you do a video on removing solder? Sucker and wick? I cant seem to master it. Also, how do you get under these old pcb boards on these amps? I never have any luck.