Thank you so much for this video (and for part 1). For years I have been reading "explanations" in forums, and OMG there is SO MUCH DISINFORMATION out there. I understand basic electronics but in the context of audio amplification without some background it is difficult to imagine how changes in components influence the behavior of AC signals. Your video does a great job of clarifying the differences between these amps that we as players have always perceived. Amazing. Thank you so much!

This is the best analysis of the differences between a Bassman, JTM45 and the Plexi that I have seen to date - thank you! I’m about to build my first JTM45 and this will help immensely in understanding the circuits.

And the Soldano is a JCM800 with higher gain structure on both series tubes along with the gain stage being higher. I’ve modified JCM800 amps for some metal players to a very close level of the Soldano.

I really loved this! I’m going to build a bassman soon with the Rob Robinette 5F6A mods: feedback switch, tone stack switch, master volume (trainwreck type 3), the one wire cascade, and adjustable bias. It was great to walk through the evolution of these circuits with you. I appreciate the knowledge.

My friend, these two videos have been the most comprehensive and well illustrated information about the history of tube amp circuits I have ever seen... And I'm a huge Uncle Doug fan, Mr. Carlson's Lab, The Guitologist, and many more for their excellent work... But this takes the cake. Subscribed and liked. Thank you so much, and keep up the amazing work. Newest biggest fan, right here. 🤘🤘🤘 I'm currently doing a "Zero dollar" Bassman build out of a Peavey Vintage salvage and my collection of parts. This has been so incredibly useful to me. I'm gonna put your videos on loop while I'm working on it. After all, you show the schematic the whole time!!! Lol. Don't know if you've already done a video on this, but I'd love to hear about the advances (or downgrades) into the JCM 2000 Era!

One more thing: The mixer capacitor, in addition to making the bright channel brighter, also makes the normal channel darker. The 5F6A fathered the greatest lineage of guitar amp circuits. But the original 5F6A was called a Bassman, so I want to use it for bass. I bought the Electro-Harmonix MIG-50, an affordable-in-the-US amp that has a circuit in this overall family, to fully convert to 5F6A / JTM45 preamp spec, and the end result gives great bass tones when used with a proper cabinet. 50 watts for bass makes it a practice / recording amp, I haven't taken it to play with my band and am worried it won't stay clean at live volume. I put the mixer cap on a switch, and the mixer cap brightening the bright channel is what hurts for bass use (except for Rickenbacker 4001/4003 Rick-O-Sound sending each pickup to each output) and helps for guitar use.

Ive watched this vid maybe ten times and it's taught me so much. Thank you

Thank you so much for these videos! You really filled in a lot of blanks!!

This was awesome. Thank you so much! I've always wondered what the circuit differences were with these amps. I knew they were similar, just not specifically how Would love to see videos like these for the next generation of big boy amps that are similar (Soldano SLO, Peavey 5150 etc..)

My 1990 reissue JTM45 utilises 6L6 GC power amp tubes. They really do sound different to EL34's. I'm currently working on obtaining a 4x10 open back cabinet for it to enhance it's Bassman loveliness.

Awesome ! Great job Sir.

I love the "sound of life" going on in the background. Ahh, children 😆

Wow you really studied these amplifiers... I was much lazier.. I had purchased a 1973 Marshall Bass amp in the late 80's... in 2000 I bought one of those pre assembled plexi point to point boards off ebay and just installed it into the bass head.. 73 was the 1st year of a pcb board as opposed to point to point.. The amp really woke up with the new board.. I also installed a MV at the same time.. also went to EL34 tubes instead of the Bass heads 6550's.. But, this was a great video... going to see what else you have posted..

Hey, mate, just wanted to thank you for this series & your Dumble circuit analysis as well. I was semi-familiar with the shifts from 5F6-A to JTM45 to Super Lead to JCM800, but it's fascinating to see that the development of that amp design, in microcosm, mirrored the macrostructural development of guitar amplifiers becoming more and more preamp-focused after Randall Smith invented the high-gain cascading preamp and released the first production-line Mesa/Boogies in 1971 or so. I know this is an old video, so you might not be seeing comments, but a couple questions just in case: which version of the Plexi did you use as your sample schematic? I'm not a Marshall devotée, but those who are tell me that the ’67, ’68, ’69, and ’70-’71 versions could all be considered different amps, and the ’73-’79 JMP circuit-board version yet another distinct entity. Bill Gerhard of Top Hat Amps, who makes phenomenal Marshall-rooted circuits (among others), says that he thinks the 1968 Super Lead was the perfect ideal of the Plexi, and that all subsequent changes were made for practical and economic reasons, not sonic ones. Also, you asked about other circuit analyses we'd like to see - since you've done this series already, I'd be very interested in a look at how the JCM 800 circuit then became the basis for so many modern high-gain amps. Soldano SLO 100, Mesa/Boogie Dual Rectifier (though it would be important to get a good later revision, since the Recto has evolved **enormously** over 30 years), Bogner Überschall, Peavey/EVH 5150, and newer crazes like the Friedman BE100 and Revv Generator as well. Thanks for all the great work!

Thank you. I've wanted this tutorial for a long time. How about a circuit analysis of the (Rivera era) Princeton Reverb ii and the Princeton it was modified on to understand some of the mods.

New subscriber here! Fantastic content man. Can you do a Marshall Plexi, Jcm 800, Friedman Browneye, Friedman smallbox, and Jose Marshall mod in depth comparison?

My suggestions for next circuits would be the Vox flavors: AC 15 to AC 30 to Top Boost to Matchless DC30 (or Trainwreck) EL84 amps with the Vox circuit and the cut control style, NFB and MV.

Differences are pretty small between Bassman and JTM45 but playing these both to compare you find that, these sounds and feels pretty different after all, even if Bassman is played through Celestion speaker.

Really interesting videos, thank you... I have a suggestion, I've heard JMPs are the same as early JCM800s, so early 800s are different than newer versions, and I'd love to go through out every difference, I did some research I found out there are different plate voltages, Cascaded input, different cap values, latter 800 have lesser filters and sound thinner and so.... So for me, one video explaining all this differences between 800s would be really interesting because I want to build a "clone". A bonus would be some modes to add more gain or something else, modes that you can bypass with a switch so you can have the stock amp whenever you want... Regards

man, when are you going to make more amp circuit analysis? I've already watched this 4 times hahahah

Great stuff! I’d love to see you do a similar breakdown on the Bassman/JTM to Sunn Model T, first generation. And even to the 2nd Gen or Red Knob Model T.

Man I just pressed subscribe button !.......wish I was a tech but will try to understand !

I get lost with schematics. Would be great to see a turretboard layout along with this type of descriptive video.

Kley, Thank you for all the circuit analysis videos. I'm a long time subscriber with a request for a video that will attract a very large viewing audience. If your up to it, will you make a Circuit Analysis video on the Peavey 5150 II (6505+) head? I truly think it will do extremely well. Thanks Kley

I liked the analisys, would you please do a Mesa mark II c + or a soldano slo. Thanks.

Very interesting. Thank you very much. I had one question though. The choke has been suppressed on JCM 800. Can you explain the impact ?

I have two JCM 800s and one is modified with an extra gain stage and some other goodies. The other is the new 20 watt studio version. I'd really like to know or understand what was done to the 2204 to achieve the high gain it has on tap but the guy who did won't spill the beans. It's probably the best amp I've come into contact with in my 30 years of playing.

Hi Kley, do you not have the AO-29 conversion amp uploaded? I did see the output transformer upgrade video, and thought the amp sounded great.. I am going to do basically the same thing and was wondering what schematic you used? I actually have a hot rod deluxe output transformer already (made by hammond though). If you could let me know the schematic, that would be great. Thanks, Tom

Now I have a kinda big question hahaha If I would want to have an amp with both the plexi 50w and the jcm 800 50w circuit (Both as they are, not mixed), I guess the way would be to put some kind of internal switching for changing to each preamp. But then in the Power section how would that work? (If i want to have everything separate so the circuits are original) Would I have give them each their 2 Power Tubes and also have a power supply for each and an output transformer for each? Or is there a way they can share both?

So where do the Master Volume JMP (76-80) 2200's fit in to all this? Are they Plexi cascaded gain master volume amps?

My tech added a feature into the JTM50 he built for me where I can switch from shared to split cathode in order to get more plexi like tones. Does that mean there is an automatic rebias that occurs in that part of the circuit to cause the kind of asymmetrical clipping to which you referred?

Why would running the low input side of the first tube at a cooler bias cause asymmetrical clipping? The high section feeding into the low section isn’t happening after a phase inverter so they’re both dealing with the whole signal with no offset?

I noticed that the bassman has a 4000 C.T. output transformer a lower value than the jtm 45... do you think this would Make a difference?

Are you sure that that is a 220k resistor on second stage B+? It's 100k on all my schematics. :/