SIGNALCHAIN
And Now For Something Completely Different…
It’s time again to take a look at all things also important to know that great sound can
tonal, with the intent of giving you even come out of trial and error.
more information to further your adventures
in making music. This month, I thought it You can make your amplifier sound better
would be fitting to share some thoughts and with a screwdriver and some experimental
advice given to me by my late, great friend, tweaking. You first need to determine wheth-amplifier-serviceman and Trainwreck amp er your amplifier has an internal bias trimpot.
designer, Ken Fischer. I was first introduced This type self-adjusts without too much trou-to Ken way back in 1981 via telephone while ble. Some amplifiers are self-biasing and can
working for Groove Tubes in Los Angeles. be voiced by substituting different brands
On the first day of
my new job at GT, my
first call was from the
extremely animated
and hilarious Ken
Fischer, delivered
in his soon-to-be
instantly recognizable New Jersey
accent. Little did I
know at the time that
I would be blessed
with all kinds of tips
and tricks from Ken
for the next quarter
century.
may like the sound of your amp running just
a tiny bit hotter, or perhaps a little bit colder.
There are many shades of great tone to be
found in this dial.
When I bought my Komet 60 head back
in 2000, I called Ken to ask him for some
advice on biasing since the Komet had
EL34 tubes and the Jim Kelley used 6V6s.
He told me that since I was already able to
bias the Kelley there
was no real differ-
ence between the two
– it was still matter
of slowly turning the
bias control and play-
ing the amplifier until
it totally rocked my
world. Granted, the
EL34s reacted differ-
ently than the 6V6s,
but I was able to hear
just where any cross-
over distortion was
rearing its ugly head
and turn the dial until
it was gone – bingo!
One of the things
that Ken often mentioned was that he
didn’t always do
things “by the book.”
Instead, he used his keen instincts and sharp
eye to troubleshoot and solve problems typically found in amps needing repair. One of
his big interests was dialing in an amplifier’s
“sweet-spot” by using his ears – not by digital voltmeter readings. Ken would always talk
about getting the most tone from the tubes
as one of his prime objectives when nursing
broken amplifiers back to health.
Ken would always say that there was a very
fine line – a balancing point – where great
tone began and where that wonderful ear
candy completely evaded you. This month’s
installment is really designed as a lesson in
how to open up your ears to the big sonic
picture and learn that there are indeed times
where a few rules can be broken in the quest
for your perfect sound. These observations
revolve around how you can optimize and
adjust your amplifier’s bias control by unusual
conventions more related to tone and musical character than just electronic criteria. It’s
An amp from the master of biasing by ear, Ken Fischer
of tubes until you hear the results you like.
Other amplifiers require some soldering to
adjust the bias circuit. These are best left to
a qualified amp technician if you’re not comfortable with the potentially lethal voltages
present inside a tube amp. If you do not
have the proper safety equipment or don’t
feel qualified to go poking around inside an
amplifier, please leave it to a professional.
You’ve been alerted to the potential hazards,
so please use some common sense and
everything will be rocking.
My first experience biasing “by ear” involved
a now vintage Jim Kelley amplifier. This amp
had its bias trimpot control conveniently
located for external adjustments – just turn
the trimpot with a jeweler’s screwdriver and
listen carefully. What Ken taught me was tantamount to my future listening abilities. The
trick is to get the amp sounding full and rich
with harmonics and overtones, but there’s a
catch – this is a matter of personal taste. You
Oddly enough, when
you look again at
the amp’s bias voltage with a digital
voltmeter after biasing by ear, the tubes
are typically within the acceptable range
of operating tolerances. This technique
is analogous to intonating a guitar at the
19th fret and then double-checking the
12th fret for any changes. You won’t really
see any change, but you sure will hear
it. This is just another method of getting
closer to the sound you want.
Thank you, Ken – it was an honor and a
blessing to know you for the time we shared.
You will never be forgotten! Remember to
make good music, have fun and be safe
above all. We’ll see you next month.
Dean Farley
is the chief designer of "Snake Oil Brand Strings"
( sobstrings.net) and has had a profound influence
on the trends in the strings of today.
