For testing, I used a Gibson Les Paul Heritage 80 model. After re-checking the chassis and cabinet connections, I turned on the amplifier, and let it warm up. I started at low volumes and progressively turned up the volume to 10, all while keeping the other settings such as presence, bass, middle and treble at 10. Upon hearing the first chords, I was immediately struck by a new “openness.” The amplifier seemed to breathe and had a new, airy sound to it – it did not sound as tight as the smaller reissue cabinet. With 30 percent more space in the cabinet than the reissue, the trebles seemed revived and the amp now had an “airy” bottom-end. Comparative testing with another stock Bluesbreaker reissue verified the tonal improvements.
An interesting side note; in 1997, Marshall produced a limited edition white Bluesbreaker called the “Limited Edition 1997.” It was basically was the same amplifier as the 1989 reissue, with one important difference: the limited edition’s cabinet incorporated the deeper 10.5” thickness, as can be found in the original Model 1962 Series II.
Step 2: The Electronics
Before digging into the guts of the Bluesbreaker, a word of caution: this phase deals with potentially dangerous electrical voltages and it is highly recommended that only a trained and competent amplifier repair person or skilled electrician perform these tasks.
This phase involves swapping out the reissue transformer, changing the 6L6 vacuum tubes to KT66s, and replacing the filter capacitors.
The Transformer and Tubes
There are now some good vintage transformer manufacturers around, so one has a choice in the matter. Since the original Model 1962 used a Radiospares (RS Deluxe) transformer, the objective here is to get one like it. When I did my conversion, I purchased a Mercury Magnetics model O45RSL- 8-M (mercurymagnetics.com).
When it comes to power tubes, the only one to use here is the revered KT66. There are however, a few brand options available. One could either purchase a matched set (two are needed) of original GECs, or purchase a pair from companies offering reissue KT66s. The European and American tubes manufactured in the 1950s and 60s (new old stock) are superior in tone, quality and reliability. Tubes now manufactured in Russia and China such as Groove Tube, the new Tung-Sol, and JJ/Tesla offer comparable tone and are reasonably priced. Since these tubes are made overseas, it is difficult to isolate a superior brand, and although tonal quality is improving with better consistency, tone remains an individual choice. For my conversion I used a matched set of Chinese Valve Art tubes, and was not disappointed.
Since we are changing out the power tubes, it is highly recommended to replace the 12AX7 (ECC83) preamp tubes as well. Again, there are several good options here which include SED Winged “C,” Electro-Harmonix and Ei/Ei-Elites. Replacing the GZ34 (5AR4) rectifier tube is also a must for optimum performance. The same tube suppliers listed above carry the GZ34, in varieties like Sino, Sovtek, or the very expensive Phillips metal base.
Filter Capacitors
Replacing the big can-style filter capacitors will definitely give your reissue more clarity. Filter capacitors are rated in the ZZxZZ format. The reissue Bluesbreaker has two 50x50ìF capacitors which must be replaced. The blue 50x50ìF filter capacitor, located closest to the GZ34 rectifier tube should be replaced with a 32x32ìF/600V capacitor. The other 50x50ìF gets replaced with a 16x16ìF/450V capacitor. JJ and F&T are two good options for filter capacitors.
Caution: These changes should only be done by a good amplifier repairperson. Also remember to have your KT66 vacuum tubes rebiased. I had renowned Bluesbreaker guru Ted Breaux finalize and tune my Bluesbreaker electronics.
Before using the amp at full volume, a suitable warm-up for the newly installed electronics should be done by simply powering up the amp and leaving it on Standby for a good hour or so. While it’s warming up, pay close attention to any unusual odors or burning, as a bad solder joint or incorrect wiring could cause a short circuit.
Once the amp has warmed up, with no guitar plugged in set the Presence, Bass, Middle and Treble controls to 10. Then start increasing the volume of Input 1 slowly, listening for any peculiar pops or sizzling noises in the process. If you don’t hear or notice anything unusual, you should be set to go.
For the “sound” test I used the same Gibson Les Paul Heritage 80; for the tonal comparison, I used the Primal Solos CD, starting with the solo in “It Hurts to Be In Love.” Before cranking the amp to 10, I employed the same gradual progression of low volume checks, listening for any unusual noises and so on. When I got to 10, I was astounded!
I was able to produce the same overtones and harmonics as the recording.
Likewise, the treble response was spectacular. I had read that Clapton used a Rangemaster treble booster with his amp, but I was getting the “sound” without one. The F9 chord in “Have You Ever Loved a Woman” shimmered and went into harmonic overload, exactly like the recording. The only notable difference was in the bass registers, as it seemed harsh at times and slightly lacking in tightness – additionally, some of the treble response seemed a little harsh. But I was definitely hearing 95 percent of that Clapton-spec sound, as no EL34 or 6L6 had ever sounded like this. It was now time for a speaker change.
| The cabinet after installing the Weber Blue Dogs |
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Step 3: The Speakers
I narrowed my choice of Alnico speakers down to the Celestion G12 Alnico Blues and the Weber P12B Blue Dogs. The Celestions were rated at 15 watts while the Webers were rated at 30 watts – I decided to try the higher-wattage Weber P12B. After swapping out the reissue Greenbacks for the new Blue Dogs, I played the amp at lower volumes for several hours. At these levels (5-6), I was pleasantly introduced to the British chime of the 1960s. Early Beatles rhythm and lead guitar sounds were easily obtainable, particularly within the mid and bass ranges.
I then tried the full throttle test. At full volume, I was in for quite a shock – the mid and bass ranges nearly cut me off at the knees. The treble side was knife-edge harsh and the amp was monstrously louder. I was obviously disappointed, as none of this remotely sounded like a Bluesbreaker. I had read that Alnico speakers may require an extended “break-in” period, and I hoped that was the case here.
I removed the Blue Dogs from the Bluesbreaker cabinet and reinstalled them into a 2x12 cabinet I was using for weekend gigs. After a few weekends of extended playing, I noticed the sound changing, as I was having to re-adjust my amp head settings. After a few more weekends, I definitely noticed something happening. It was now time to re-install the Blue Dogs back into the Bluesbreaker cabinet.
Upon trying it again, something magical happened to the overall sound of the amplifier. Right there in my basement, and out of my rebuilt Bluesbreaker, came the sound. I was flabbergasted, as it sounded incredible. I must have played the amp all night. I was nailing all of Clapton’s Bluesbreaker riffs, and they sounded identical to recordings. The A minor solo break in “All Your Love” sounded amazing, and like the recording, it was drenched in sustain and overtones. “Stormy Monday” from
Looking Back was spot on.
Finally, my Bluesbreaker renovation was complete. The amp sounded just like it should, some 40 years ago. Doing this yourself makes all the difference, as you become a part of the equation – with a little work and dedication, you can experience Marshall just as Clapton discovered it.