Build the Amp Maker PP-18 Baby Bluesbreaker Kit

Amp Maker (www.ampmaker.com) is a Suffolk, England based maker of tube amplifier kits, started in 2005. Their design approach is to make good tone affordable. The Amp Maker line of kits today include:

• Woodface 55 (WF-55) - Their easiest to build kit, with 4 watts of tweed-voiced tone with a mahogany control panel. The Woodface WF-55 uses the simplest circuit design of any guitar amp ever produced: the Champ. In 1955, Leo Fender tweaked the circuit of his 'cheap and cheerful' Champ to create the famed 5F1, or Tweed Champ. The result was a fantastic little amp - with a warm and woody tone when clean, and a great raunchy crunch tone when the amp's cranked. The WF-55 uses the same signal path circuit together with a slightly modified power supply, to lower the Tweed Champ's inherent noise level and make the amplifier cheaper to build. Just like the original, there's one control for volume.
  
  

• Single-Ended 5A - is a 5 watt single-ended Class A amp, with treble, middle and bass controls. Gain and Master volume allow for balancing preamp and power amp distortion. A three-band tone stack (treble, middle and bass) allows you to fine-tune your guitar tone. It's a typically 'British sounding' amp, with a bright tone full of harmonics when overdriven. With the distortion available, it feels considerably louder than a cleaner amp, such as the 4W WF-55.
  
  

• Double-Six 1/6/12 - is an amplifier designed for a wide range of clean tones. Most amps are built for maximum gain a have a narrow range of clean tones. The Double-Six has independent treble, middle and bass controls for a wide range of clean tones. It ships with two 6V6 tubes, but it will also run with one or two 6L6s, or one 5881/EL34/KT66/KT77/KT88. The power level is switchable between 1, 6 and 12 watts. There's also a Fat switch to compensate for single-coil pickups, and a Boost switch that removes the treble and bass controls to give a raunchy, overdrive tone.
  
  

• PP-18 Vintage Plexi - is a "baby Bluesbreaker" in an easy-to-build guitar amp kit. The PP-18 circuit uses the Normal channel circuit of the 18W Marshall of the mid to late '60s. Like the original Marshall it has simple preamp with just tone and volume controls and a no-frills cathode-biased 18W power stage. This combination creates a dynamic, touch-responsive medium-gain amp that's perfect for blues and classic rock. The kit uses British-made transformers, Mallory 150 signal capacitors and a hand-wired turret board.
  
  

• SL-18 SuperLite TMB - This kit starts with the PP-18 circuit (above) and adds the preamp from the Single-Ended 5A (above) to provide more preamp gain; treble, middle and bass (TMB) controls; and a master volume for balancing preamp and power amp overdrive that is reminiscent of the mid-1970s style of overdrive tone.
  
  

• PP-36 18-36W Plexi - The PP-36 uses the same circuit as the PP-18 but adds two extra EL84 power tubes and a GZ34 rectifier tube to provide up to 36W of output. It features a continuously adjustable power output level between 18 and 36 watts. This provides some interesting "in-between" tones. For example, at about 9-o'clock on the 18-36W dial, one pair of EL84s are being fully driven for maximum overdrive, while the other pair of EL84s are being driven much more lightly, and mixing in a cleaner tone.
  
  

THE WATKINS DOMINATOR

Now that we've covered the line of Amp Maker kits, let's take a closer look at one model, the PP-18 Vintage Plexi. The origins of this design begin with a man named Charlie Watkins - a British audio engineer and musical instrument maker, who is notable for pioneering loud PA systems for outdoor rock festivals. His company Watkins Electric Music (WEM, www.wemwatkins.co.uk) was founded in 1949, and in 1957 he released the Watkins Dominator amplifier.

This amp is famous for its colorful look, spectacular sound and two angled speakers that Watkins thought would better disperse the sound. The amp has 4 inputs so a whole combo could plug-in and perform through a couple of raw EL84 tubes operating in push-pull mode. The Dominator was the inspiration for the title of Mo Foster's 1997 book "17 Watts?: First 20 Years of British Rock Guitar, the Musicians and Their Stories." The story told is that the title came from a school band member's question of "do we really need that much power?" when a 17 watt Watkins Dominator amplifier was acquired as a replacement for the aging 5 watt amp they had previously been using. Let's give a listen to this demo of the Watkins Dominator:

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Dominator was a significant amp in its own right, but it was also important as it formed the basis for Jim Marshall's first 18 watt amplifier design that would come to be known as the "Baby Bluesbreaker."

Marshall was a successful London drummer and teacher with a small shop selling drums, cymbals and accessories. At the request of some customers he started to carry guitar equipment, most notably Fender amplifiers from America. These amps were very popular but also very expensive. Marshall thought he could produce his own less-expensive alternative to the American amps, and began with a Fender Bassman as the basis for his first product, eventually named the JTM 45. This model was configured as an amplifier head with a separate 4x12 (four 12" speakers) cabinet. The phrase "plexi" is often used in describing some Marshall models due to the use of a plexiglass type material for the control panels, which began with this model.

THE MARSHALL BLUESBREAKER

Around this time, according to legend, Eric Clapton asked Jim Marshall to build him a combo amp (amp and speakers in one cabinet) that would be powerful enough to use on stage but still fit in the trunk of his car. This led to the first Marshall model #1961 with four 10" speakers which was used by Clapton until it was lost during travel in Greece. Marshall replaced it with the model #1962 with two 12" speakers. The reputation of this amplifier was formed when Eric Clapton, who had just joined John Mayall & the Bluesbreakers, used one to record the historic Blues Breakers with Eric Clapton. After that, the amplifier came to be called "Bluesbreaker." Listen to this track, "Hideaway", from the album to hear the Bluesbreaker amplifier in action:

A typical Bluesbreaker amp put out 35 watts and therefore would break up more quickly than larger amplifiers. This was the quality that Clapton wanted, since the best sound came when the amp was played at full volume. Larger amplifiers were just too loud to use in this way, but with 35 watts Clapton had the sound engineer mic the amp from across the room while he played it as loudly as possible, as if playing live. With this amp, Clapton and Marshall set the standard for electric guitar tone. According to Aaron Pittman's excellent "The Tube Amp Book," the following are the key reasons for this tone:

• KT66 power output tubes produce a round, bell-like tone with soft distortion.
• 12AX7 phase inverter section produced more compression and distortion.
• Open backed cabinet made of dense baltic birch plywood, with two 12" 20-watt Celestion speakers placed side-by-side was well suited to recording.
• Different resistor and capacitor values in the passive tone circuit allowed for more gain and shifted the frequency curve up and out.
• Higher B+ plate voltage on the tubes produced a more aggressive tone, especially when coupled with the hot alnico humbucker pickups of Clapton's Les Paul.
• Increased negative feedback compared with the Bassman amp, which gave greater emphasis to even-order harmonics characteristic of Marshall amps.

THE MARSHALL BABY BLUESBREAKER

Beyond the great tone, Marshall also succeeded in his design objective of lowering cost, with the "Bluesbreaker" selling for about one half the cost of the American Fender Bassman, and about one third less than the British Vox AC30. But Marshall also wanted to better compete with lower priced amps, particularly from Vox, and set out to develop a lower power combo amp.

As mentioned above, Marshall used the Watkins Dominator circuit as his starting point to produce the model #1958 18 watt combo amp with two 10" Celestion speakers. This amp used three 12AX7 (ECC83) preamplifier tubes for high gain, a pair of EL84 power output tubes and an EZ81 tube rectifier. With a "plexi" panel and snakeskin grille these amps looked and sounded much like a smaller version of the Bluesbreaker, leading to the moniker "Baby Bluesbreaker."

One key to the sound of the Baby Bluesbreaker was the tube rectifier, which "sagged" at high power. "Sagging" in this context means that at higher power levels the internal resistance of the rectifier tube rises somewhat, creating more voltage drop across the rectifier, and less output voltage from the power supply. This means that on loud peaks the plate voltage of the tubes drops or "sags" a bit, which momentarily lowers the gain of the tubes, effectively causing some compression of the signal. The final key to the Baby Bluesbreaker sound was the use of the EL84 power tube, which have their own distinct sound that is often described as "sweet." When driven to full power they become more brassy with a distortion characteristic described as "brittle" and evocative of the the Vox amps of the day.

The model #1958 was released in 1964 and discontinued in 1969, a victim of the "bigger is better" trend where guitarists sought out amps with 50 to 100 watts. However since that time many guitarists have learned that great tone in a small package is highly desirable. As more players learned that small vintage amps yielded great tone at more usable volumes a funny thing happened - the small amps began to sell for about the same price as the big amps in the vintage market. If viewed on a dollar per watt basis, vintage model #1958s command about five times the rate of vintage Marshall JTM100s. These small amps are now priced out of reach for the player who wants to take them on gigs. Fortunately there is an alternative that delivers the best of both worlds - tone and price. This brings us to the Amp Maker PP-18 Baby Bluesbreaker Kit.

THE AMP MAKER PP-18 VINTAGE PLEXI KIT

There are many circuits and kits available to recreate the early 18 watt Marshall amps (see www.18watt.com for much more on this topic). We've chosen to feature the PP-18 as it is a complete kit that was designed to be easy to build and as inexpensive as possible, at around $370.00. That's for the time saver kit with pre-punched AC02 chassis as well as front and rear gold 'plexi' control panels. A less expensive version is available if you're retrofitting another amp with a new turret board.

The PP-18 uses the normal channel circuit with just tone and volume controls. It is a dynamic and touch-responsive medium-gain amp that's perfect for blues and classic rock. At 18 watts it's loud enough to keep up with most drummers for pub and small club gigs. The kit uses British-made transformers and Mallory 150 signal caps - all hand-wired on a full-size British-made turret board. The build rates a 2 on Amp Maker's complexity scale of 1-5. One thing that makes it easier is a hand-made turret board that takes any guesswork out of laying out the amp's components and wiring. This photo will give you an idea of the straightforward layout of the turret board.

The kit building is guided through a very nice online construction manual which we suggest you review before purchasing. Our review showed it to be clear, detailed, well illustrated and with a nice procedure for testing. Here's a look at the completed chassis.

Finally, check out a demo of this amp below, and visit www.ampmaker.com to learn more about the kit, pricing, shipping and other models.