Copyright 1999, 20th Century Guitar Magazine.
In the June 1996 issue of 20th CENTURY GUITAR MAGAZINE, I wrote
an article that described how to make a clone of a Fender AB763 Vibroverb
("Project Vibroclone"). That project proved to be wildly popular and to
this day I receive inquiries from people who are building their own Vibroclone.
Another "how to" project of mine is re-creating a Fender 6G7 Bandmaster.
This project will probably not be as popular as making a Vibroclone, but
the results are still very cool and worthwhile.
The other neat thing about this project is that, unlike Project
Vibroclone, no fiddling with the electronics is necessary. All you need is
a Bandmaster amp chassis that is already in good working order (hint: take
it to your tech for a tune-up) and a custom-made cabinet to put it in.
First, some background - the 6G7 Bandmaster is a rare amp.
It was only made for a few months in very late 1959 through about mid-1960.
It has a 3x10 speaker configuration just like the tweed 5E7 Bandmaster that
preceded it, but it has a horizontal chassis with front controls and is
covered in brown tolex. Fender modified the Bandmaster circuit in Fall 1960
(6G7-A) and dropped the 3x10 combo design for a piggyback arrangement with
a 1x12 tone ring speaker cab, later switching to a sealed 2x12 cab.
Photos, from top: Cutting solid pine boards
for cabinet; Special template (on workbench) used to cut finger joints; Finger-jointed
boards glued and ready for assembly. Upper right: The final product: Project
|The Bandmasters available
for use in the project include the blonde (6G7-A), blackface (AB763), and
silverface (AB568, AA1069) models. The model that most closely resembles
the original 6G7 circuit is, not surprisingly, the 6G7-A. The main difference
is the more complex (3-tube vs 2-tube) vibrato circuit on the 6G7-A. The early
6G7-A's (late 1960 through 1961) have an 8-ohm output transformer just like
the '60 6G7 (transformer part no. 45217). The later 6G7-A Bandmasters (late
1961 through 1963) have a 4-ohm transformer (transformer part no. 125A6A).
The blackface and silverface also use this 4-ohm tranny and will work just
fine though they won't look quite as authentic and will sound different due
to their different circuitry.
Just to digress for a moment_ there is one other Fender amp
that is closely related to the 6G7 Bandmaster that can be used for this project,
namely, the brown Pro. The earliest version from 1960 (6G5) is identical
to the 3x10 Bandmaster right down to the middle volume control and 8-ohm
output transformer. The only difference is that the Pro was mated to a 1x15
speaker cabinet. The later Pro (6G5-A) is identical to the 6G7-A piggyback
Bandmaster circuit and would work well, too. Although their circuits are
very similar, I would not recommend using a brown Concert or Super for this
project since they already have multiple 10-inch speaker configurations.
Please note (seriously!) - do not go crazy and try to modify
your vintage Bandmaster for this project. If you want an exact replica of
the 6G7 circuit, build one from scratch. Chassis and components for such an
undertaking are available from several suppliers. This intent of this project
is to use an existing amp without modification of any kind. The beauty of
this idea is that it preserves the vintage value and aspects of the "donor"
Photos, from left: Master cabinet builder
Jeffrey Suits assembling cabinet; Cabinet is checked for squareness during
the clamping and glue-drying process; Inside of cab is stained just like Fender
did in the old days.
For my own project I used a '61 6G7-A Bandmaster. This amp
has an 8-ohm output transformer and was a good choice for me since my efforts
to find an original 1x12 tone ring cab came up empty (though I found a bunch
of 4-ohm 2x12 cabs during my quest). Again, the overriding factor here was
not to compromise the originality of the amp in any way. The project is
completely reversible since it simply requires moving the amp chassis from
one cabinet to another.
The next thing I needed was a combo cabinet and I turned to
Gregg Hopkins at Vintage Amp Restoration in St. Louis for a faithful recreation
of the original. To me, this was the most important aspect of the project
and it had to be perfect. I wanted the amp to look like a very early 6G7 so
I specified a cabinet with no metal corners, a sharp, flat, front-top edge,
and grill cloth used on tweed Fender amps. I was really pleased with the
results and even the color of the stained interior matched that found on
Fender amps from 1960.
For Project Bandmasters that use blackface or silverface donor
amps, the combo cabinets can be made with the appropriate cosmetics, i.e.,
black tolex with silver sparkle grill for the blackface look or black tolex
with blue sparkle grill for the silverface look.
At the time that this project was underway, speaker selection
was somewhat limited. The original 6G7 used either Jensen P10R or P10Q speakers
and I wanted to capture the sound of those speakers in this amp. I could
try to find original Jensens or go with modern "vintage style" speakers.
Since the output transformer of my amp has an 8-ohm impedance (and changing
the transformer was forbidden under the "no butchering of vintage amps"
proviso) I needed to use 16-ohm speakers. Three 16-ohm units wired in parallel
yield a total impedance of 5.3 ohms which is close enough to 8-ohms that
I wouldn't have to worry about stressing or blowing the output tranny.
It is interesting to note that the original 6G7 Bandmaster
used three 8-ohm speakers for a total impedance of 2.7 ohms which is a 3-fold
mismatch for the 8-ohm output transformer. Post-tweed era Fender transformers
(mainly Schumacher units) were very tolerant of up to a 2-fold mismatch
in output impedance. This is why most of the brown, blonde and blackface
amps have and extension speaker jack. You can run your Deluxe Reverb with
an 8-ohm extension cab (yielding a total impedance of 4-ohms) without a
hitch. Perhaps the 3-fold mismatch on the 3x10 Bandmaster is part of the
secret to its great sound.
Finding three, original 16-ohm Jensen P10Q speakers seemed very unlikely
and the reissues were not yet available. That left me with MojoTone P10R clones
and WeberVST P10R or P10Q speakers, all of which were available in 16-ohms.
I opted for the WeberVST P10Qs because it has a larger voice coil than the
R-model speaker and can handle more power. Ted Weber has also been considering
the idea of making these speakers with 12-ohm voice coils which would yield
a total impedance of exactly 4-ohms for three speakers
wired in parallel. This would be the perfect setup for those Bandmasters
with 4-ohm output transformers (the vast majority of Bandmasters out there
are 4-ohm units).
The WeberVST P10Qs come with removable magnet covers. The speaker
fit on the baffle board was perfect, but the clearance between the magnetic
cover of the upper left speaker (when viewed from the rear of the amp) and
the transformers was very tight. The easiest thing to do is to remove the
magnet cover from that one speaker (or all of them for consistency), but since
nothing was touching or rattling I elected to keep the cover in place.
The final cosmetic details needed were a "flat" Fender logo,
brown knobs and a cover. The logo was no problem since I used the one that
was on the Bandmaster head cab. The blonde Fender amps, such as my 6G7-A
Bandmaster, were fitted with blonde controls knobs and the brown Fender
amps, such as the 3x10 Bandmaster, were fitted with brown knobs. Brown repro
knobs and amp covers are available from a number of suppliers and I ordered
these through Vintage Amp Restoration. The knobs were installed without a
problem and the original blonde knobs were stored along with the head cab
for safe keeping. The cover is a repro brown Victoria cover that looks authentic
and does a great job of keeping the kids from fiddling with the amp's knobs
when I'm not lookin'.
Photos, from top: Stain colors are accurate
and made from a "secret blend"; Table router used to bevel edges of cab; Gregg
Hopkins measuring and cutting brown tolex; The donor amp - a 1961 6G7-A Band
The only electronics tweaking that I did for this project was re-tubing
the amp. Tube selection is quite good these days with quality offerings
from current makers as well as new old stock (NOS). The 40-watt brown and
blonde Fender amps have some pretty high operating voltages that often approach
the 500VDC mark. This Bandmaster (and my brown Pro) have a B+ voltage of
495 so sturdy power tubes were in order.
The Svetlana 6L6GC is a good choice when considering a currently
manufactured tube. I opted for a pair of NOS Sylvania 6L6GC and adjusted the
bias to 33 mA per tube at idle. These have a transparent, glassy sound with
good bottom end and strong mids. For the preamp tubes, I went with a NOS
JAN Philips 12AX7 for the phase inverter and vibrato, and a NOS RCA 12AX7
for the first gain stage of each
channel. The RCAs have a warmer sound compared to the Philips 12AX7s which
How does it sound? Good. Real good. Better than my '63 Concert!
It has the classic Fender clean sound. It will overdrive, but man is it loud
when this happens. The WeberVST speakers are very efficient and don't get
flabby or muddy sounding. They produce strong, tight bottom end, but not
at the expense of high-end chime. A Fender Reverb Unit will thicken up the
sound (and who doesn't like reverb?) turning the 3x10 Bandmaster clone into
a great rock or blues amp. I suspect harp players might like it as well.
As an aside, some people may be wondering if "Project Bandmaster"
is a blueprint for making intentionally fraudulent 3x10 Bandmasters. To the
untrained eye it would appear that way, but nearly all the 3x10, brown,
6G7 Bandmasters have a "middle" volume control, i.e. -the controls are laid
out Bass, Treble, Volume. All subsequent Bandmaster have controls that are
laid out Volume, Treble, Bass. So, the VTB control layout is one clue though
it's not flawless because while I was preparing this article I was contacted
by a gentleman who owns an original 1960 6G7 Bandmaster (3x10) which dated
to May 1960 and had the later Volume, Treble, Bass layout!! Another clues
to the originality of a 6G7 Bandmaster is the lack of an extension speaker
jack on the back of the chassis along with the mysterious Pulse Adjust hole
and 5 preamp tubes (6G7-A's had 6 preamp tubes). So, while my Project Bandmaster
could pass as the real thing at first glance, closer scrutiny would quickly
reveal that it's not. And Project Bandmasters using blackface or silverface
donors don't stand a chance of being passed off as an original.
So there you have it. A 3x10 Bandmaster using a genuine vintage
Fender amp, but at a cost that is about one-third (or less) of an original.
Got a blonde, blackface, or silverface Bandmaster head laying around? Use
it for a Project Bandmaster donor_ you'll like the results!!
Photos from top: Grill cloth is stretched
and held by a wenzeskillian clamp while pneumatic staple gun fastens cloth
to baffleboard; Covering a cabinet is an art form and it takes skilled hands
to get the corners just right; Clearance between the WeberVST P10Q magnet
cover and transformers and power tubes was very tight, but not a problem.
About the author: Greg Gagliano's lucky number is 3 and
that's why he likes his 3x10 Bandmaster.
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