Produced between 1987 and 1992, the Fender
Champ 12 is a 12-watt, 1x12 combo with a
single 6L6 power tube and a pair of 7025 preamp
tubes. Photo courtesy of telecaster.com
I have a Fender Champ 12 from the late ’80s that I’m curious about. The input jack is
broken, and it has never been re-tubed or probably even serviced since it was new. I’ve
given up on trying to get any useful, adjustable gain out of it, and the reverb is pretty
much just full on or off. I primarily use it as a practice amp at home, typically at lower
volumes, and I’d love to get tones similar to a Fender Tonemaster. Is that possible?
When a customer brought his Champ 12 in
for service years ago, a couple of this amp’s
unique “innovations” had me scratching
my head. There are aspects of the electronic
design I’ve not seen in any other Fender amp.
The Champ 12 I repaired had multiple
problems: Its output was low and distorted,
and it wouldn’t switch channels. Before
pulling a schematic on the unit, I took
a few minutes to troubleshoot it. Sure
enough, the output looked very bad on the
oscilloscope, and there was no low voltage
for the switching circuitry. When I started
tracing the wiring associated with the
switching circuitry, it unexpectedly led me
to the output stage! I figured this can’t be
right—someone must have already gotten
their inexperienced, grubby little paws into
the amp and moved some wires.
It was then I realized what was actually
going on. The amp had been designed to
tap voltage off of the cathode circuit in
the cathode-biased output stage as a low-voltage
source for the switching circuitry.
Wow, I hadn’t seen that before. I checked
the resistors in the cathode circuit, and
then replaced one that was way out of tolerance.
That was it—the switching circuitry
now had voltage and the output of the
amp was great. Okay, I won’t forget that
the next time a Champ 12 comes in with
the same set of problems. But let’s move
on to your amp and see if we can address
some of your concerns.
The first thing I’d suggest is to re-tube
the amp, especially if that has never been
done before. You may hear a noticeable
improvement. Also, be sure to have
the cathode resistors in the output stage
checked, as we already know what kinds
of problems they can cause. I’d also recommend
having the broken input jack
replaced. It’s generally the number 1 input
jack that breaks and typically that’s the most
useable input for guitar.
Being a 10–12 watt amp, the Champ 12
is, of course, never going to sound as big
and bold as the 100-watt Tonemaster, nor
will it have that kind of distortion unless the
entire circuit is completely rebuilt. So what
I’m shooting for is to bring the amp’s tone
closer to the Tonemaster.
We’ll start with the tone stacks, as
they’re noticeably different in these two
amps. Locate the three main capacitors in
the Champ’s tone circuit—C3, C4, and
C5. Replace the 250 pF ceramic cap (C3)
with a 150 pF with at least a 250V rating.
Next, replace the 0.1 μF (C4) with a .047
μF 400-600V. Feel free to use the original
C5 cap here, as C5 will be replaced by a
0.022 μF 400-600V cap. This should set
up the tonal characteristics to be closer to
You mentioned the amp didn’t have
much gain adjustability. This may be due to
the type of “shunt-to-ground” volume controls
(something I generally don’t care for)
used in the Champ 12, but if you’ve found
the gain is a bit too loose and broken up, I’d
suggest changing the value of C1. Using a
25 μF capacitor on the first gain stage can
sometimes provide too much amplification
of the lower frequencies, which can muddy
up the overdrive. I’d suggest switching the
locations of C1 (25 μF) and C8 (0.68 μF).
Install the 0.68 μF capacitor in the cathode
stage of V1A and the 25 μF capacitor in the
cathode stage of V1B.
Another option would be to switch the
locations of C1 and C12, instead of C8.
This would place the 25 μF cap one stage
further down the line.
You mentioned that the reverb is delivering
all or nothing, but this may be due to
an incorrect adjustment. The reverb in these
amps is the other unique “innovation” I
mentioned earlier. It’s actually driven by the
signal going to the speaker!
I had seen this done before in early amps
from a different manufacturer, but not in a
Fender. It seems this unique design requires
the proper adjustment of an internal pot to
work properly. I won’t go into the procedure
for this because you can find it on Fender’s
supplied schematic for this amp. If you
have this adjusted properly, it may make
your reverb a bit more useable, although I
wouldn’t expect full reverb bliss from this
Last and definitely not the least, I’d
encourage you to change the speaker.
The Tonemaster came stock with either a
Celestion Vintage 30 or Celestion G12-
80, both of which would sound substantially
different from the stock Fender
blue-label speaker currently in your amp.
I hope these suggestions make your amp a
real Tone Champ!
is one of
the godfathers of the
low-wattage amp revolution,
co-founded and was
the principal designer for
Budda Amplification. Jeff recently launched EAST
Amplification, and he can be reached at