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The
Purpleheart
(Click here to see more pictures)
Pictured above is one
of three EL-34 based Purpleheart Amplifier Heads that I designed in
the late 1990's. I built 3 of these amplifiers total - 1 prototype
and 2 for production. The wooden cabinets were built by Matt
Friedman of Acacia Instruments [Custom Basses--Unfortunately as of a
few years ago, he is no longer building his beautiful basses]. The
chassis is 1/8" thick aluminum. All parts are standard JCA Circuits
fare--PEC and Clarostat RV4N Series Sealed 2 Watt Pots,
Silver/Teflon wire, Angela Ceramic Sockets, NKK Heavy Duty Switches,
Mallory, LCR, Cornell Dubilier Capacitors, Dale RS Series Power
Resistors, and Xicon 1 Watt Carbon Film Resistors. The amplifier
also uses MOV protection on the AC power switch. The Output
Transformer is one of Joe Pampel's fabulous Obsolete Electronics
Incorporated [OEI] "Plexi" 3.4K transformers. The power transformer
is a sturdy CCS rated Hammond 300 series. The amplifier is fixed
bias. The rectifier uses FR307 Fast Recovery Epitaxial Diodes in a
Full Wave Center Tap configuration. The amplifier delivers 38 Watts
RMS at clipping @ 1KHz input with EL-34's. It delivers 21 Watts RMS
at clipping @ 1KHz input with 6V6's. The bias set device is actually
a locking Kilo Dial Counter for a Clarostat 10 Turn Pot. It's a
great way to set the bias easily and I love it. I use this setup
with all of my fixed bias amps because it is just so easy to swap
out tubes depending on the situation. I have been using this
particular Kilo Dial Counter and Clarostat 10 Turn Pot since the mid
1990's. Let's say you want to use favorite pair of XF2 Mullards for
the stage or a wonderful pair of RCA Grayplates for the studio. A
simple swap between these takes about 2 minutes or less. Once I show
guys how to use this setup, they find that it is simply a matter of
keeping a note with the particular dial setting for a favorite pair
of tubes and setting the dial to that number when installing them.
The controls from left
to right are Input, Volume, Treble, Mid, Bass, Presence, Standby,
and Power. It has an IEC AC Mains Receptacle, Mains Fuse, Bias Test
Points, Output Stage Fusing, an Ohmite Brand Rotary switch for
4,8,16 Ohm selection, and a parallel pair of Speaker Output Jacks.
I originally built the
first prototype using a Purpleheart Cabinet, Valence, and Faceplate
as well as a Pau Amarillo wood JCA Circuits logo inlay. This
amplifier in the photos also uses the same cosmetics and wood
selection as the prototype. I also built one with a Purpleheart
Cabinet, Bubinga Faceplate and Valence, and Ebony JCA Circuits
inlay. I sold the Bubinga amp to a fellow co-worker over 4 years ago
who uses it extensively throughout the Philly scene. In over 4
years, I am proud to say that he has never had a single failure or
problem of any kind. His cabinet is really beat up though from
countless gigs, but the amp functions perfectly. I like that he
really uses the amp and that it is a much tougher amp than it might
appear. He used to use JCM 800 and JCM 900 100 watt tops. He thinks
that the 38 watt Purpleheart amp is more than loud enough, and
basically outdid his Marshalls for sheer volume and tightness
through the same cabs!
The circuit contains
elements of Dave Reeves' fabulous HiWatt DR103, Jim Marshall's
classic JTM45, and Ken Fischer's superb Trainwreck Express. I was
really in my Trainwreck inspired stage very heavily in the mid/late
1990's when I designed this amplifier. It uses a Plexi/Vox style
preamp with a cathode follower and a somewhat HiWatt inspired Long
Tail Pair phase inverter. Cosmetically, it is certainly Trainwreck
inspired. However, the circuitry is a completely original JCA
Circuits design which is not a clone of anything out there. But I
will say that Ken was very complimentary in his positive comments
about my design work and the sound quality of this head. It has
oodles of power, tightness, and gain. It's a very sweet lead amp.
This has a bit more gain than the GR 1.6 yet is still very quiet
with little shot noise, thermal noise, only 8mV of actual 60Hz hum
cranked using modern Russian tubes, and is just generally well
behaved using only AC on the filaments. It's kind of an uncanny
circuit. With a good selection of distortion pedals, the right
technique, and guitar, I have been able to pull off very convincing
Jerry Cantrell/Alice In Chains types of "Chunge" tones with this
head set up with 6V6's! No squealing headaches from obnoxious
feedback either. The amp takes pedals extremely well. Using the
beautiful and classic EL-34 power tube, cranked up, this amp is just
pure balls to the walls thick, searing harmonics without the need
for any pedal help. The circuit was actually designed around the
EL-34 power tube and it's characteristics. Going straight into the
amp with my PRS Standard 24, I am getting the most delicious, round,
complex harmonically dense clean tones out there. The amount of
actual imaging and clarity is simply out of this world! The EL-34
takes on the role of providing a very linear, solid and "close"
sound. Cranking her up leads up a bit more into edgier territory.
The amp delivers the epitome of the perfect "Woman Tone". Going a
bit further, the amp slides into Leslie West territory. With a P-90
the amp is just purring along for your "Nantucket Sleighride" if you
like. Then, moving on with the volume about 80%-90%, it just kicks
and screams with more "Modern" heavy tones. Borderline Boogie sear.
Very killer indeed. EL-34's are simply Awesome in this circuit. I
really love this power tube. This is certainly not a bedroom amp at
all though! 21 watts [6v6's] or 38 watts [EL-34's] through a
Mesa/Boogie Thiele ported cab loaded with an EVM 12L has tons of
tight bottom with enough crunchy harmonics to pull off any job you
might have. Playing through a Vintage 4X12 with a quartet of 25 Watt
Greenbacks or AlNiCo Blues will take you back to the roots of great
playing and tone. Playing through a nice JCM 900 Lead Celestion
cabinet with G-12T75's will give great power chord work a huge
soundstage. Using the right pedal will deliver the nastiest tones
from this amp. That's how I am able to nail the heavier side of
things using a pair of 6V6's in this circuit. The high efficiency
and tight damping of the fabulous OEI 3.4K OT, the huge, heavily
rated CCS rated Hammond 300 series PT, and the very nicely tweaked
out feedback circuit coupled to a sweet and quiet preamp makes for
very surprising results with the 6V6 and EL-34 tube choices. I like
to do things a bit differently, yet simply using highly tweaked
classic style circuitry.
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