The
BLUESBREAKER:
Revisited
The Model 1962 reissue schematic
one dedicated to the tremolo circuit. The
Mullard GZ34 rectifier tube was again used.
Two can-type filter capacitors were used:
one LCR 32µf x 32µf at 600 volts mounted
on top of the chassis near the output transformer, and a second LCR 16µf x 16µf at 450
volts mounted inside the chassis.
Speakers
The amp’s speakers consisted of two 12”
Celestion G12s, rated at 20 watts, 15 ohms,
and with an Alnico magnet. These speakers
were essentially the same as those used in
Vox AC30s, and are extremely fragile when
pushed beyond their limit. Because Clapton
ran the amplifier at full volume, the Alnicos
may have been damaged. He may have
replaced them with the higher wattage,
ceramic magnet Celestion Greenbacks.
The Objective:
Convert a Reissue to Clapton-Spec
I started my investigation into obtaining
this sound over 20 years ago. In addition to
the “Beano” studio CD, there were other
John Mayall albums that included “live”
cuts from Eric Clapton’s time with the
Bluesbreakers. Although these recordings
were done with crude equipment, they
captured the raw and unrestrained sound of
Clapton’s guitar and amplifier. To my ears,
these recordings were most realistic, as
they lacked any studio treatment. I quickly
knew what sound I was after.
In 1994, Mike Doyle’s book, The History
of Marshall, was released and included an
eye-opening chapter on the Bluesbreaker.
That chapter confirmed the reissue’s lack of
authentic sound, and it became obvious that
in the amp’s conversion to Clapton specs the
only salvageable pieces would be the electrical chassis, the control panel and some
of the cabinet hardware – the cabinet and
speakers would have to be replaced.
With that, I decided to do the conversion in
a logical progression and planned to document the progress. I preferred a progressive
approach, as it would give me a chance to
analyze each change made separately. In
addition, since this conversion would be fairly expensive, it would be easier on the budget to purchase items over a period of time.
The changes required could be grouped into
three categories:
1. Cabinet: Since the reissue cabinet was
too small, it could not be used. I’d have to
find a new cabinet that is the correct size.
The reissue’s casters, amplifier strap handle
and the plastic Marshall logo badge could
still be used.
2. Electronics: Swap out the reissue output
transformer for a vintage correct one, re-tube
with KT66 vacuum tubes and change out the
filter capacitors.
3. Speakers: Change to an Alnico magnet type.
I should note that it is possible to make
deeper changes, such as replacement of
the circuit board, resistors, potentiometers
