Carl's Custom Amps British Bluesmaster 20W to 1/10W JTM-45 Style head with Power Scaling

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Carl's Custom Amps
Las Cruces, NM, United States
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About This Listing

Carl's Custom Amps

British Bluesmaster 20W to 1/10W JTM-45 style head with KT66s
Finally a JTM-45 with the ability to control the volume!

Carl's Custom Amps is high demand please allow 10 to 12 weeks for your amp to be built, tested and shipped.

This is for the 20W version but I also offer a 45W and 45W+ version. For most players 20W is more than enough power. 

You can choose your tolex and piping colors!

For the foreseeable future build times will be between 10 to 16 weeks. We are experiencing very high demand. Each amp is built one at a time with great care so no rushing is possible. Thank you to everyone who has purchased for your business and patience!


Early Marshall amps were incredible—-rich, thick, bluesy and mean! There just something about a KT-66 loaded early 60’s JTM. Jimi Hendrix, Eric Clapton, Angus Young, Joe Perry and countless others have used them. However they too loud to be used by most players. They are great pedal amps but the real magic is getting the amp to sweet spot. The British Bluesmaster delivers all those early Marshall sounds but is fitted with London Power so you can get real power tube overdrive at low volumes. The volume can be controlled as transparently as possible from full power down 1/10W.

The channels are internally jumpered so you don’t need a patch cable. Also we’ve added a bright boost switch to the amp (not pictured) so the amp is more useful darker guitars or if you want little more bite. The SAG (the tube rectifier effect) is completely variable so you can go from solid-state rectifier sounds to tube rectifier sounds and beyond!

London Power’s Power Scaling:

The 60s and 70's Plexi are incredibly  loud amps and were designed for big stages.  They too loud for most players to use even in a club setting.  The British Overdrive series features variable power which solves this issue. Power Scaling allows the player to dial in anything from full power down to 1/10W. So these amp are capable of playing anything form a bedroom to a stadium.  Many amps have  "wattage" and "power" controls that sound unnatural. London Power’s Power Scaling  is different from most of these and very transparent.  Plus in any setting below full power it extends the life of the power tubes.  

Other Features:

Linked Input:  

The amp has a linked input so there no need to use a patch cable to jumper channels. This allows you to blend the sounds of normal and bright channels.

SAG Control:

One of the cool things about JTMs was the bloom of notes that comes from the use of tube rectifier. The one trouble is that the sag is set meaning you cannot get more or less and that the sag changes with volume changes. Instead of the tube we’ve added SAG control. It allows the user to adjust the sag/compression and makes the amp more reliable!

Tube Swapping:  

The 20W, 45W and 45W+ Watt versions all come with KT66 power tubes but can use any of the following power tube types with re-baising: EL-34, KT77, 5881, 6L6WGC, 6L6GC, 6V6 or 6550s. Bias ports and externally accessed bias pots allows the user to swap tubes. The 20W and 45W version uses two power tubes and the 45W+ version uses four power tubes for the bigger “100W Marshall” feel without the extra volume. Two of the power tubes in 45W+ version can be pulled for the two tube power section sound with no affect on power output.


All tube,  Bright and Normal volume controls, boost switch, Crisp/Stock Switch, Vibe Switch (Negative Feedback)  treble, mids, bass, and presence, power and limit controls,  ON/ OFF Switch,  hand wired for great sound and reliability with a method that shortens the signal path, super quiet grounding for low noise, special resistor selection for low noise and great tone, adjustable fixed bias, solid state rectifier.

Malory 150 and Panasonic Tone Caps, Panasonic/Nichicon Ultra Long Life Filter caps, Heyboer Hammond Output transformer, custom made toroidal power transformer, Cliff jacks (made in the UK), aluminum chassis, 12 ft power cord JJ's Tubes.

Don’t waste your time or blow out you ear drums—get awesome tone!

Customer Comments:

 “I reached out to Carl a few months back, and explained to him what I was looking for in an guitar amplifier. I was looking for the that gritty, bluesy, dirty, sweet tones of the yesteryear. He recommended his British Bluesmaster with the London Power Scaling Design. I had never heard of London Power Scaling, but it sounded pretty intriguing. An amplifier that could get that heavenly cranked JTM-like tone, even down to a whisper volume, if needed. This amp sounded like it was just what I was looking for. So I said "lets do this", Carl said 'will do".

 So fast forward a little bit. I now have the Bluesmaster in my possession, I'm chomping at the bit to hook it up and hear her sing! Now here'e thing, it took me a solid week to learn to dial in the overdrive, not because it was difficult, but because the clean tones on this amp are some of the best that I've ever heard! No kidding, maybe the best. I just kept wanting to hear it clean. So sweet, full, dynamic and responsive, even without reverb. And I'm a certified reverb junkie.Now add a little bit of reverb to it and it's like a walk in the clouds!

But enough about the clean tones, it's the dirt and grime that people want to hear about, and this circuit does dirt very well! And it will get this great overdrive from bedroom volume, to noise ordinance violation summons volume! Just some small adjustments to the power and limit knobs will take you from the edge of breakup, to head long over that edge! It's hard to explain to someone what great tone is, but you know it when you hear it! I dig this amp, a lot. “

 Josh C.

“After a delightful evening tweaking my Bluesmaster, I can put my perceptions into a review. You may comment as you see fit. Here we go.

I received my Carl’s Custom Bluesmaster 20 watt a couple of days ago and find it to be the best amp I have ever come across. I’ve spent a fortune trying countless tube and solid state amps, all high end, and while they each have their own great sound, none produced what I heard in my head, but I got by with the gain just high enough to “put hair on it,” without sounding like a 14-year-old who doesn’t know how to use his new distortion pedal. Not to mention the fact that most of my practicing is at home, where I could never really let the amp move the speaker, and the sound was ultimately never satisfying, often frustrating to the point of blunting my interest in playing.

Not so with the Bluesmaster. Right out or the box I recognized that basic tone, flowing, creamy and singing, and all your recalled tones from the early 1970’s come rushing back. The guitar sounds “true” with the Bluesmaster driving humbuckers though the old 212 Celestion cab. The London power scaling (“Variable Power”) takes a bit of experimenting with (like with that exotic seasoning that was missing from your favorite dish), but after a few hours practice, I use the Limit control as a volume knob (employing the actual wattage knob as a sort of gain governor). True to Carl’s instructions, keep the “Limit” level lower than the wattage level, and the creamy overdrive stays genuine (as opposed to reminiscent of a gain pedal, never quite there), just as you remember from those priceless LPs. What you hear out of a Bluesmaster is almost like some  fundamental timbre that separates this from all the modelling amps (and many tube amps) out there, ever closer, but still hopelessly far away from what those of us who know that sound from “back in the day” are seeking. Open chords sound like a roar, but with a tight, smooth character, no circuit-generated gravelly candy sounds here.

It’s difficult avoiding the use of wine-tasting jargon, but Carl’s new Bluesmaster amp is enough to satisfy even the most frustrated jaded cork sniffer. My only concern is that I can’t stop playing it. If vintage Marshall is what you’re hearing in your head but never through your ears, give a Carl’s Custom Bluesmaster a listen in a real live setting, and you’ll feel right at home.

Bravo. “

Dennis O.

Reviews of this Shop


Product Specs

ConditionBrand New (New)
Brand New items are sold by an authorized dealer or original builder and include all original packaging.learn more
Made In
  • United States

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