I had a blast building and testing two Marshall 18-watt kits for a Premier Guitar story — and I emerged with new respect for this cool 1965 design.
These mini-Marshalls were neglected in their day, but are now treasured. The oft-heard claim that they provide plexi tones at reasonable volumes is only partially true — these are open-backed combos powered by a Vox-like pair of EL-84s tubes. But while they have roughy the same horsepower as the era’s Fender Deluxe and Vox AC15, their tone is undeniably ’60s Marshall. In the studio, they sound far larger than their actual size. And out of the studio, they’re still pretty darn loud.
I’ve never seen three 18-watts in the same place before.
Even though the Mojotone and Tube Depot kits I built share the same schematic (and identical cabinets, both made by Mojotone), the build experiences and final results differed greatly.
And just when I thought I’d scaled the Everest of 18-watt ecstasy, I get a real Marshall 18-watt reissue for an upcoming Premier Guitar review. Stay tuned.
Are any of you guys 18-watt fans? Any observations to share?
It is amazing how different the same EL84s can sound in different amps. I have a Blues Junior that sounds pure Fender and an Orange Tiny Terror that sounds completely different—both powered by EL 84s. I find 18 watts is sufficient in a band that plays at a reasonable volume or a louder situation where I am miked. Heaven help me, though, if I get stuck with 18 watts in a loud band with no mic.
Yeah, totally — you could use an 18-watt to play with a light-touch drummer like Joey Waronker, but a heavy-hitter like Brain would leave you in the dirt!
I've been rocking the Suhr Badger 18 for the past few years and I've loved it. Unique tones, easy to dial in and really push those tubes to feel the magic. Cathode biasing is nice too. Super easy to maintain. Wish I got on board sooner!
I recently repaired a Fender Pro Junior for a friend. He had had it for over 25 years, apparently without it being serviced.
It had deveoped an annoying crackle. The loudspeaker was shot (a Fender branded Emminence) which wasn’t helping, so I replaced it with an Emminence Legend (I found out later these amps shipped with either an Emminence or an inferior Oxford loudspeaker). The crackling turned out to be heavily oxidised valve bases, a common problem with the upside down Fender chassis where all the heat from the valves rises and cooks the bases and other components. I tried cleaning and re-tensioning the bases but eventually I just replaced them.
Like a lot of these small amps the Pro Junior has no bias adjustemnt, so I thought nothing of it and replaced all the valves with high qaulity new ones. After that the amp was never really happy and it ran really hot! As I discovered, the new EL84’s biased nothing like the original Fender’s, heaven knows how they managed to mass produce these amps. I guess their original valve stock was really consistent and they just selected the fixed bias setting to suit. Eventually I fitted a bias trimmer and a new pair of JJ EL84’s. The amp sounded much better but it had a ton of gain … and hum!
I experimented with fitting the different gain versions of the input dual triode – 12AX7 (as originally fitted), 12AT7 and 12AU7. This made a huge difference. The 12AU7 was great for clean tones, but I ended up with the 12AT7 as a good compromise on gain and clean tone. Apparently a lot of people don’t rate the Pro Junior (ones with the crappy Oxford speaker perhaps?) but after all the fiddling around over a period of several weeks the amp ended up sounding pretty good.
Which leads me to speculate if, when people talk about different valves (even the same valve type but from different makers) having a radically different sound, the biggest difference is actually in valve gain. After all most valve amps have little to no negative feedback to control gain.
As for the same output tubes sounding different in different amps … well the circuit configuration, operating voltage, output transformer, loudspeaker and cabinet have a big influence on the sound of the amp. These little 18 Watter combos do have a sound space of their own due to mostly 10inch loudspeakers and small open back cabs. Oh and check out Bill Machrone’s website on the Blues Junior – https://billmaudio.com – I found it really helful when working on the Pro Junior. Sorry about the long, long post.
Don’t apologize for the long post — it’s very interesting! 🙂
Reminds me of a funny story I heard: Someone told me that the head of a large musical instrument company (‘Im not naming names, ’cause this is second-hand gossip) had said, “The EL84 is the greatest-sounding tube ever created, because I can get them for 75 cents each.”
Really like my Tubemeister 18combo. Nice and small just wish the clean channel matched the dirty one in volume. EL84s are a change from the 6L6s in my Fender for sure.Looks like you had a good bit of fun in that build process, nice article very good read.
A few questions…
1 – how do they like a clean boost at the input?
b) – what’s the relative weight of the two output transformers (approximately)?
iii: any guess on benefits of implementing other tone stacks, like with a concentric knob? Maybe a mid/treble thing if the bass is already not too prominent.
One of the crazy things about most tube amp designs is that they normally have an input gain stage immediately followed by a passive tone stack, which on all settings introduces a huge gain loss! And most Mid controls don’t do anything you can’t do with combinations of the Bass and Treble.
Also most tone stacks don’t operate the way you might expect. For example you might think setting bass and treble to 5 would give you a flat response. Well far from it! It’s worth playing with Duncan’s Tone Stack Calculator (or other similar app) to see exactly what your tone stack does https://www.duncanamps.com/tsc/index.html. Of course you can say that how tone stacks sound is the most important thing, but I find its instructive to see what they actually do to the frequency response.
Hi Terry, I’m familiar with the Duncan tone stack program. My curiosity arises because I think that single tone knobs were mostly economic decisions in the original designs. Why is it good to have a 3-band control on a 100W design but not on an 18W design? Put another way, does the 100W design really need a 3-band control, or is it there simply to satisfy the need for more apparent “features” per cost? Passive tone control parts cost is pretty minimal.
Hi Jermaine,
Yup, I think you are right, the single tone control is to keep the cost down. As far as I can tell the tone control in this circuit is strictly a bass cut filter that shifts its -3db point between 125Hz and 400Hz. Switching it out altogether might give a bit more low end. The 3 band controls usually appear on the more powerful and expensive amps, so yes its a more apparent features thing. Although having both Bass and Treble controls does give you a bit more tonal flexibility – at least you can choose to cut either bass or treble or cut the mids. As I said the third Mid knob is pretty redundant and on a lot of amps with just Bass and Treble the Mid control position in the tone circuit is just replaced by a fixed resistor.
As far as cost savings go, all the early guitar electronics, including amps, was built to a very, very tight budget and to a price point. So saving maybe 1$ on parts, plus labour costs to wire them was a big deal. Most of the early guitar electronics would perform better from an engineering point of view if it had the parts left in to the design that were removed in order to save on manufacturing costs. For example the story goes that the Wah Wah pedal was invented because Brad Plunkett’s line manager had told him he had to save money by designing a cheaper tone circuit for the American builds of the Vox Super Beatle amplifier.
I meant that as an example of how nit picky cost saving in the guitar electronics industry was, rather than an example of parts being removed. Although the standard Vox style Wah Wah pedal itself is pretty minimal on parts and as a result it has a rather low input impedance and a rather high output impedance. Which is why it doesn’t like driving a Fuzz Face (another example of a pedal using minimal parts) which has a very low input impedance.
I’m so glad you you did this article. I noticed you mention this amp one of the other videos, I had wanted to request a story about it, and low and behold here it is.
I recently bought a Weber 6M36 kit. This is like the 18 watt with two extra power tubes for a 36 watt version. I haven’t started building yet, so I was really interested in hearing about your experience.
Same here! I haven’t tried a Weber kit yet, but I’d love to.
I’ve had a couple of Blues Juniors over the years, but managed to kill them by touring them across Canada in the dead of winter. It’s interesting how different each iteration of that design has sounded: recent versions behave radically different than the first edition.
I’m currently using a Jet City 20 head with my rock band. They’re pretty freakin’ loud, so there’s not a lot of headroom, but jeez, that thing has got some serious rock’n’roll attitude, a bit like a hotrodded JCM800 with less volume and bass on tap – altogether a different beast than a Blues Jr. or AC15, and eminently useable.
In the GP article you mentioned previously building a Ceriatone clone with various mods. I wondered if you could comment on how it sounded vs. the Mojotone / Tube Depot units you built, I expect the components [esp. transformers] might have some effect on the overall tone. Thanks!
Great question. I didn’t say more, though, because the topology is so different. My Ceriatone has both the three-band tone control AND the EF86 power tube. It’s a little ruder/looser than the others, but MUCH noisier.
I’ve built several Ceriatone kits, and recommend them. But they’re almost no documentation. For beginning kit builders, I’m tempted to suggest starting with Tube Depot just because the docs are so great.