Dear Amp Man,
Please write a column about the Pignose G40V. I have not
used mine in five years, so I’m curious what’s necessary to
get it up and running. Also, please discuss any mods, like a
standby switch or speaker/line out. I have replaced the factory
speaker with an Eminence Legend. Also, what are your
thoughts on converting the G40V to a head, since its cabinet
is so small? Thanks!
—John Mitchell, Escondido, CA
Hi John,
The all-tube Pignose G40V in
its compact, portable glory. |
Surprisingly, I don’t believe
a G40V has ever crossed my
bench over the years, but I did
some research and found that
these inexpensive, all-tube amps
are a great little find. You get a
40-watt, dual-6L6, 1x10 combo
for not much money—very
cool. The G40V was designed
for Pignose by Dennis Kager,
who many amp freaks know
from his days with Ampeg,
as well as his own company,
Sundown. Cooler yet! The basic
circuit is pretty simple and very
similar to an early master-volume
Marshall. In other words,
it’s a good candidate for a bit
of modification. But let’s get to
your initial questions first.
An amp that has been sitting
this long is more than
likely going to need a bit of
electrical cleaning. You’ll need
to invest in a couple of cans of
electronic cleaner—one with
lubricant and one without.
Clean the input jack and the
pots with the lubricant cleaner.
Clean the tube sockets with
cleaner only. Due to limited
space, I won’t go into cleaning
details right now, but I’m
sure you can find instructions
online if you need them.
Also, as a general practice,
many techs recommend that
you “reform” the electrolytic
capacitors in an amplifier that
has been unused for years.
While I don’t believe that’s necessary
for an amp that’s been
idle for only five years, if you
have the ability to do this, it
certainly wouldn’t hurt.
Warning: Working inside an
amp is very dangerous—it can
even be lethal. So if you are not
familiar with the inner workings
of a tube amplifier and the
possible hazards involved, please
have this work performed by
someone who is.
To do this, remove all the
tubes and connect the amp to a
Variac or similar variable line-voltage
device. With the Variac
set to zero volts, turn the amp
on. If you have the ability to
measure the B+ (high) voltage
in the amp, attach your negative
meter lead to a good chassis
ground point and connect the
positive lead to the center-tap
lead of the output transformer.
From here, you’ll be able to
measure the B+ immediately
after the rectifier circuit. Turn
the Variac on and slowly raise
the level until you measure
approximately 50 volts at this
point. If you do not have the
ability to measure internal voltages,
this would more than likely
be a setting of 10 to 15 volts
on the Variac. From this point
on, there really aren’t any particular
“correct” intervals between
increasing the setting, but every
10 minutes or so, raise the
Variac approximately 10 volts.
Do this until the Variac setting
reaches 100 volts. You can
then lower the Variac to zero
and turn off and disconnect the
amp. This process should have
raised the caps to near their
maximum voltage ratings.
Why didn’t we raise the
Variac to the full 120V AC
line level? With no tubes in
the amp, there is no load on
the power supply. With no
load on the supply, the supply
output voltage becomes
substantially higher and would
stand a good chance of over-voltaging
the filter caps. If this
happens, the caps can explode.
Confetti everywhere! It looks
like someone just had a New
Year’s Eve party inside your
amp—not good.
If all is well with the amp,
at this point you should have a
functioning G40V. Now we can
move on to the extras.
You mentioned adding a
standby switch, and I think
that’s a good idea. Vacuum
tubes should be at operating
temperature prior to having
high voltage applied to them,
and I’m sure its omission on
this amp was purely a price-point
issue.
But you can install one, and
here’s the most effective way I
see to do this. Locate the two
red leads attached to the power
supply circuit board that come
from the mains transformer.
Disconnect both leads from
the circuit board. Install a good
quality DPST (double-pole/single-throw) switch of your
choosing on the front panel
next to the power switch.
Connect these two red leads to
a left and right set of terminals
on the switch. From the other
left and right set of terminals
on the switch back, run a new
pair of wires to the initial
circuit-board connections. You
now have a standby switch to
save those tubes.
You also asked about converting
the G40V to a head,
since the cabinet was so small.
Personally, I wouldn’t do it.
Being that the amp is not
much bigger than a large amp
head anyway, why give up the
option of having a portable,
self-contained combo amp for
rehearsals or small gigs? To play
larger venues, all you need to do
is unplug the internal speaker
and connect the amp to a 2x12
or 4x12 cabinet—in essence,
using the G40V as a head. You
currently have the best of both
worlds, in my opinion.
Next month, I’ll talk about
adding a line out and discuss
a few more possible modifications.
Until then, keep dreaming
about playing that cool
little piggy!
Jeff Bober 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
pgampman@gmail.com.