Mojotone British 45 Kit

I almost always play small combo amps of 20 watts or less. But I wanted something with a bit more clean headroom for a possible upcoming project — and to demo my stompboxes. I’ve always enjoyed playing JTM-45s when I’ve reviewed them for guitar mags, so I ordered Monotone’s British 45 kit.

I’d previously had a great experience building Mojotone’s Marshall 18 watt clone kit when I reviewed it for Premier Guitar a couple of years ago. It turned out great, and I use it regularly.

Mojotone provides high quality parts, nearly labelled and organized in plastic compartmented boxes. But beware: The company provides no build instructions — just a layout diagram and a schematic. You need amp building experience or help from an expert. Click play for a slideshow about he build:

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This is Mojotone's new offset head cabinet. (The amp chassis first in other Mojotone cabinets as well.)

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The two power tubes can be either EL-34s or KT-66s. (I chose the latter, just for a new experience.)

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The parts come neatly labeled and organized in plastic bins — a BIG help!

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Warning: the kit includes no build instructions — just this layout diagram and a schematic.

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I ALMOST managed to assemble it, but I needed a rescue at the end. (Thanks to Bruce Clement of BC Audio, a brilliant boutique builder here in San Francisco.)

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Mojotone supplies their own branded transformers (which sound fab).

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It's a turret board build. (The board and turrets are pre-made, as opposed to some kits, which require you to insert the turrets yourself.)

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This is probably not a good first build — maybe start with a nice little tweed Champ kit?

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The a plexi faceplate, which I left omitted. I also substituted my own knobs.

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I nearly made it through myself. (Translation: I soldered everything together and it didn’t work.) So I had to hire Bruce Clement of BC Audio here in San Francisco to rescue me. (Bonus: Bruce loaned me one of his JTX50 heads. Man, it’s one of the best-sounding Marshall derivatives I’ve ever heard. It’s among his Octal-Plex series amps, which use octal preamp tubes in Marshall-inspired designs.)

While Bruce was sorting out my bonehead mistakes, I asked him to add a post-phase investor master volume (which sounds great, and provides convincing crunch at relatively low volumes). He also swapped a cap to make the bright channel even brighter, which is useful for mixing the bright and normal sound when the channels are jumpered. In fact, I tend to adjust tone that way, rather than via the tone stack. (If I did this build again, I’d link the two channels internally, as Bruce did on his JTX50.)

The JTM-45 is a very close cousin of the Fender tweed Bassman — the schematics are nearly identical. (I always figured that Marshall swiping Fender’s design was Leo’s karma for swiping the Bigsby headstock profile.) But even though the circuit is plagiarized, the use of British tubes, speakers, and enclosures lends a unique sound. The amp (or at least its combo version) is inevitably associated with Blues Breakers-era Clapton, so naturally I have zero desire to use it that way. While the amp provides gorgeous power-amp distortion, I’m tending to use it at cleanish settings, where it provides a nice showcase for my gnarly distortion pedals. It’s a loud contraption with tons of headroom, at least compared to my usual modest combos.

This was a great build experience, despite my tech shortcomings. The amp’s tone can stand up to any number of handmade JTM-45 derivatives costing twice as much. But I definitely don’t recommend it as a first DIY amp project. Better to start with Tube Depot’s cool little tweed Champ kit, a relatively simple circuit board build with superb assembly instructions by Rob Hull. (You can hear it here.)

Thanks to Logan Tabor and Andrew Simmons of Mojotone — and to Bruce Clement of BC Audio for rescuing my sorry workbench ass.

25 comments to Mojotone British 45 Kit

  • trevor deke bajus

    Man, I love how EL34s sound clean. So incredibly overlooked.

    • Joe Gore

      Actually, you hear the KT-66s here, but I agree with your essential point, Trevor: Squeaky-clean Marshall is SUCH an overlooked and underused sound. Back in my first serious bands, when I was playing mostly clean-toned African- and Afro-Caribbean-influenced guitar, I used a master volume 100w Marshall through a 2×12 cabinet. Simple, Fela-style single-note lines were just SO authoritative. I’ve always like that sound and wished more players made use of it.

  • Davin

    If you don’t mind my asking, what were your “bonehead mistakes” as you put it? I’ve built one amp without any errors (shoutout to the BYOC Tweed Deluxe and their stellar instructions) but now that I’ve got that in my blood I expect I’ll tackle another one soon and probably won’t have as much luck.

    • Joe Gore

      I messed up the connections at the rectifier tube. (And while he was in there Bruce found something else screwy, but I forget what.) I’ve never made a BYOC amp kit, but I’ve built a LOT of their pedal kit. It was one of the main ways I learned to make pedals. Keith V.’s build instructions are simply superb. (I’ve done work along those lines for clients, and it’s HARD!) I’m equally impressed by the amp kit instructions Robert Hull created for Tube Depot kits back when he worked for the company. Frankly, my advice is to either a) get something with good instructions, or b) have someone lined up who can help, and be prepared to pay a bit.

  • Ian Gray

    How timely! Thanks for this, I have been eying up the Bluesbreaker clones for the last fortnight, thinking one would be my next build project. That said, I feel a tad nervous about plunging into the MojoTone kit given your experience and the paucity of instructions. In closing, I really enjoy your approach of writing comments rather than trying to be the usual YouBoob host/presenter who comes off as distracted, falsely friendly and usually pretty much not someone whose playing I want to return to ever again. There ought to be standards and in my vote, you set the level of the bar. Thanks again.

    • joe

      Hiya, Ian! Thanks so much for your kind words here and elsewhere. I appreciate it even more than you might expect.

      I love the way my two Mojotone kits sound. But for solid documentation, check out rival products from BYOC and Tube Depot. I built Mojotone and Tube Depot 18-watt clones for a Premier Guitar review a couple of years ago. I slightly preferred the sound of the Mojotone kit, and that’s the one I play. But they were both fine amps, and the Tube Depot kit includes Robert Hull’s superb construction manual. I haven’t tried the BYOC amp kits myself yet, but if the documentation is of the same quality as their pedal kits, it’s awesome. They really do it right.

  • Skot Jakubiec

    Very nice amp/sound, and beautiful playing as always. I look forward to you posting clips with you playing. I have a copy of a JTM45 as well, though I don’t know which manufacturer- a friend built it for me 15 years ago. When I used it through the obvious 4-12 the bass response was overwhelming and basically muddy and unusable. But once I started using it with an open backed 1-12 with a celestion G12H it really came alive! It is also a great platform for experimenting with various V1 and PI tubes. I am using 6V6s (with a bias adjustment) right now, but I think I prefer the KT66s.

    • joe

      Oh, cool! The amp sounded great with the EL-34s too. I probably should have made some benchmark recordings, but I was too eager to play with the new amp. My vague sense is that the KT-66s are a bit more full-frequency — lower lows, airier highs — at the slight expense of what we think of as that signature Marshall midrange thing. I’ve never owned a KT-66 amp before, and most of the JTM-45s and spinoffs I’ve reviewed over the years had EL-34s, so I’m just sort of going for the novelty. 🙂

      The THD cab, which I’ve had since the mid-90s, is weird and cool. It’s got two 10s and one 12 (its nickname was “Mickey Mouse” cab ’cause the baffle cuts look like him). It’s also got a semi-open back: not wide-open like a combo cab, but with perhaps a 4-inch-wide opening in the back, so it diffuses more like a combo and less like a 4×12. I recently replaced the original THD Longhorn speakers with new Celestions — two Gold 10s and a Creamback 12. I love the Creamback, which I’d heard in several review amps, and in the Carr Lincoln combo I got last year.

      Your setup — with the G12H and open back — probably sounds great! 🙂

      • mwseniff

        I really like the KT series of tubes in general and they do sound different than their pentode cousins. In case you don’t know KT stands for kink-less tetrode. So these tubes have only 4 active elements lacking the suppressor grid of it’s pentode cousins 5 active elements. The design of the tube reduces and almost eliminates the kink in the power curve graphs that is present in the pentode tubes. I think they have a smoother sound with a sort of burnished overdrive when pushed. I have the EH reissues in a few amps and they sound quite good I can’t really compare them to the NOS because I used my last NOS KT-66s up in my Ampeg VT-40 12 years ago. The new KT-88s make my friends with Dynacos pretty happy. I have a pair of KT-120’s I am considering putting them in my Fender Super Twin (150 watt amp). That pair of tubes will replace 6 6L6s should be stupidly clean and loud great for pedals. The amp sounds great in the demos. Unlike many folk I really like a clean sound from a Marshall style amp, they seem to have their own sparkle.

        • joe

          Thanks for that — I hardly knew any of that stuff. Well, except one thing: clean Marshall tones can be awesome. (I got the habit when I was in a mostly African band in my early 20s, where I played nothing but crispy-clean sounds through a 100-watt Marshall.) But I’ve hardly touched an amp over 20 watts in the last decade or so, so the big-bottle thing feels like a new experience to me. I want to hear more about those KT-120s — something I’ve never even heard of!

          • mwseniff

            They are a higher wattage / higher voltage new version of the KT-88. There is also a KT-150 that is capable of more power yet and a Kt-90 and a KT-100a also exists, Bob Carver uses KT-150s in his new monoblocks very high end hifi gear. These are all made in Russia by Mike Matthew’s factories and are sold as Tungsol branded. You can check them out at the New Sensor/Electro-Harmonix website. If you buy them get them burnt in and matched by someone that knows how, New SensorEH seem to do a good job. That last piece of advice goes for any output tubes even S-E amps as it catches the duds and you get a stable tube with long life. I actually have been toying with the idea of using a KT-150 as an S-E class A amp like a Champ on steroids it might be an ideal pedal platform if I can find an output transformer for it I can afford.

  • Like I suspect everyone that follows Tonefiend I really look forward to your new posts – the demos are so great to listen to.

    Interesting you mention the post phase inverter master volume, I wonder how well this mod usually tracks. In theory you want the two outputs from the phase inverter to present equal drive to the two output valves (or however many valves in pairs there happen to be in the output stage). I don’t know how well the two tracks in a typical dual pot match each other.

    On the other hand it makes sense that the phase inverter may be adding a lot to an amps distortion character (and so you want to include it before a master volume) because, apart from the considerable attenuation of the usually passive tone stack, each stage in an amp adds gain so it seems to me more likely that the phase inverter is going to start clipping before the input stages.

    • joe

      Hi Terry! In my experience, the PPI master volumes tend to sound very convincing, at least at less-than-extremely attenuated levels. This entire demo was recorded with the master at 50%. In my recent video on two Carr amps, I demonstrate taking it WAY down — like, heavy distortion at literal whisper levels. It sounds shockingly decent.

      Now I’m curious about an amp design that omits the tone stack entirely (well, maybe a low-pass pot or switch if absolutely necessary) but where you adjust the spectrum by solely balancing jumpered bright and darker channels. On this amp, I find myself tweaking that way, and almost never touching the dedicated tone pots.

    • Martin Beer

      I had wondered about the pot matching issue, but I’ve tried checking the resistance of a cheap Alpha dual pot at various points along its travel, and the two tracks varied by only a couple of percent. That’s probably as close as the fixed resistors in the original Marshall. I guess that might change as the pot wears though.
      Omitting the tone stack could be interesting, but it might turn the amp into a fire-breathing gain monster, as the stack is quite lossy.

  • Blake Cooper

    Joe, I am absolutely enchanted by your playing! Can’t say when or if the time will be right for me to build one of these beasties, but I sure enjoyed build pictures and comments. A lovely demo!

  • Martin Beer

    That sounds great, I’m surprised at how clean some of those sounds are. I built an amp based on the later ’60s 1987 circuit, and find I really have to keep the channel volumes low or roll back on the guitar volume to get it to clean up like that. Maybe I should try more of a JTM45 preamp with the shared cathodes for the next one.

    • joe

      Hi Martin. Hmm — that’s interesting to me! Granted, hardly anyone ever uses those squeak-clean Marshall tones, but I don’t usually have trouble summoning them (and they sound great, contrary to conventional wisdom). I wonder why you have that issue! (Terry probably knows.) 🙂

      • Martin Beer

        The preamp voltage is at the lower end of normal on the amp I built, which might make it a little dirtier, and there are a couple of differences in gain and voicing with the 1987 circuit that take it in a crunchier direction. That one was for a friend who likes it that way, so I didn’t tweak it further, but I might go more JTM45ish when I build one for myself – yours certainly sounds sweet in the video.
        But maybe part of it is just me adjusting after playing a blackface Fender-ish amp with low gain and that big midrange dip they have – I find it almost a bigger change than swapping guitars!

  • Skot Jakubiec

    This talk of an amp eliminating the tone stack really intrigues me- like a tweed champ in big boy pants. I’m a minimalist at heart, and I see the amp as the actual instrument, the guitar simply the controller. I like the idea of taking the sound/character of the amp, and working with that, instead of a “do-all” type of thing. That’s why I love my ’69 champ- it definitely has a character. When I adjust the tones knobs on the champ or my JTM45 copy, there isn’t a drastic effect- you still hear the amp, just slightly different shades of it. As far as I’m concerned, I could get rid of them, and with manipulations of my guitar controls and my hands, get all the variety I would need. Maybe just the hi and low inputs. I have often considered having my champ modded to a tweed circuit, but I haven’t had the balls to mess with an almost 50 year old amp that way yet- though I know it is just a matter of time.
    I had a newer ampeg GVT5H that had a Baxandall eq and that had a dramatic effect when messing with the tone, but the amp sounded “blah”- not having it’s own sound. I prefer to hear the amps personality.

  • Skot Jakubiec

    On a side note- is there an easier way, that I am overlooking, to navigate to the older blog posts on this site, other than just working my way backwards on the previous post link? I seem to remember at one point there being a list by month along the right margin. I like to look through and reread all the old blogs and comments. Also, my heart wouldn’t be broken if you posted videos of your playing on a daily basis!

  • ray

    I know I’m a couple of months late to the comment chain here but I just have to thank you for pointing out that Marshall amps can be great clean too. My “keep it forever” amp is a humble 1995 Bluesbreaker reissue that I’ve owned since new. I do the wound up to ten distortion thing through it for fun every now and then but my personal sound (such as it is) is based on running the amp in a clean and deep sounding manner. The sort of sound that you might associate more with a blackface Fender. I love it and the amp works great with the embarrassing number of effects pedals I usually have plugged in the front end. Over the years I’ve tried the Bluesbreaker with all sorts of 6L6’s, EL-34’s and KT-66’s up to and including some original GEC KT-66’s I found back in the 90’s. My favorite has proven to be the KT’s. The GEC’s died ages ago so I’ve been using modern KT-66’s for quite a while. They sound fine to my ears.

  • SlickRick63

    Joe.
    You have an interesting vibe going on that really comes through in your playing style.Thank God for giving us uniqueness. It’s what keeps music alive!

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