BRINGING A GIBSON DUO-MEDALIST BACK TO LIFE, PT. 1 BY JEFF BOBER
hi Jeff:
I recently traded my Vox
Valvetronix VT50 for an
old Gibson Duo-Medalist.
Although the online comments I initially found about
the Duo-Medalist were lackluster, I’ve come across articles that tout the untapped
potential of this old tube
amp—they even cite [legend-ary Trainwreck amp builder]
ken Fischer to support this
claim. Though I’m a novice, I
have a friend who is capable
of performing electronic
surgery. I was wondering if
you could shine additional
light on this amp and weed
out fact from fiction concerning its mod potential. For
your reference, I’ve attached
information I’ve found online
about the Duo-Medalist,
including its schematic.
by the way, the amp’s
footswitch is MIA, so I can’t
engage the tremolo. I’m curious whether we can perform a
miracle on that, as well.
Sincerely,
Tommy kirst
of Gibson amps in that publication, but that’s not to say that
Ken didn’t supply this information somewhere at some point
in time.
The bottom line is that
the modification mentions
removing a few resistors and
capacitors to improve the amp’s
performance. I’ve taken a look
at the schematic, and it’s my
opinion that this modification
should definitely improve the
frequency response and increase
the gain of your amp. Let me
explain the modification and
then give you a better way to
execute it. We’ll then also look
at a few other potential modifications that can make your
Duo-Medalist even better.
In the initial modification,
we will be removing an RC
(resistor/capacitor) network
in the preamp stages of the
Normal and Reverb channels.
It appears that this was incorporated to set the frequency
response of the amp. Removing
this will definitely change its
tonal characteristics, but since
you aren’t happy with the performance of the amp anyway,
we’ve got nowhere to go but up.
In looking at the schematic,
we can see a network of three
resistors (470k, 220k, and 220k)
and three capacitors (330 pF,
470 pF, and .0068 µF) attached
to pin 5 on both V1 (the
Normal channel) and V2 (the
Reverb channel). Since this is a
multi-chassis amp, your friend
will need to remove the Duo-Medalist’s preamp chassis—the
chassis containing all the preamp
tubes—to locate these parts.
Now, although I said we would
be removing these components
from the circuit, that doesn’t mean
we need to completely remove
them. I’m going to give you a way
to execute this that’s both substantially easier and reversible, should
you ever wish to return the amp
to its stock circuitry.
This schematic for a vintage Gibson Duo-Medalist can also be
downloaded at gibson.com/Files/schematics/duo-medalist.jpg. Image
courtesy of Gibson Guitar Corp.
The 2-channel Duo-Medalist in all its ’70s glory. Photo by David Hilts
Hi Tommy:
I’m glad to see you’ve found a
cool old tube amp! But simply
having tubes doesn’t guarantee
an amp will sound great. Some
amps need a bit of help before
they can ascend to the “pretty
cool” category. Let’s see if we
can raise the cool factor of your
Gibson Duo-Medalist.
In your email, you supplied
me with some posts and links that
mention information supposedly
supplied in The Trainwreck Pages
by the late, great Ken Fischer. I
knew Ken and was familiar with
the original Trainwreck Pages pub-
lished in the Angela Instruments
catalog of many years ago (this
fantastic parts catalog was obvi-
ously a true labor of love for
Steve Melkisethian at Angela
Instruments). There’s no mention
Locate the tag board terminal
where the wire from connector
S2 Pin 1 attaches. This should be
the start of the RC network. Now
locate Pin 5 of V1 (the 6EU7 clos-
est to the side of the chassis). This
is where the RC circuit connects
to the preamp tube. Run a short
wire from the S2 Pin 1 connection
to V1 Pin 5. Now locate the .0068
µF capacitor that is part of this
network. One side of it should be
connected to a grounded terminal.
Leave that lead connected and dis-
connect the lead that’s attached to
the junction of the two 220k resis-
tors. Lifting this lead will eliminate
any additional noise from being
injected into the signal path.
JEFF BOBER, one of
the godfathers of the
low-wattage amp revolution, co-founded and was
the principal designer
for Budda Amplification.
Jeff launched EAST
Amplification in 2010, and he can be
reached at pgampman@gmail.com.
