with over 650 live gigs listed - Mag 4 Live Music

FREE EVERY MONTH Scrumpy ‘n’ Western EXTRA
FACTS ABOUT AMPLIFIERS
Or did you know Part one
If you use an electric guitar or electro
acoustic then you will be using an amplifier
which will come in various sizes from a
small 10 watt practice to anything larger!!
This article is really to give you a better
idea of what you are really using and my be
of help with a bigger purchase in the future.
An amplifier takes a tiny electrical current
and turns it into a much bigger current that
will move loudspeaker cones. The first devise
that could do this was a valve, and the
‘amplification tube’ was patented in about
1906 (oddly enough by two people , who
were working on the same idea but independently.)
The early audio amplifiers were
huge devices with each section of the circuit
forming a separate unit in a rack. The
first known electric guitar design dates
back to the early thirty’s, but the first purpose-built
guitar amplifiers appeared in
America in the 1940’s and were modified
from radio set circuits. Leo Fender had
started ‘Fender Radio Services’ in the early
1940’s as Radio was the then modern
technology of it’s day. The first guitar amplifier
to use transistors, available to buy
commercially was the Burns Orbit combo,
made in Britain about 1963 (Burns being a
top UK brand) The 40 watt combo sported
a tremolo circuit and there were a number
of variations, based on different speakers.
At that time, this ground breaking design
was more expensive than the valve combos
on sale at the time! Where as today a
valve combo will cost far more. Today guitarists
spend a lot of time arguing with
other guitarists whether valve amps are
‘better’ than the many modern designs that
seek to emulate the valve sound. This
could be a complete waste of time as for a
number of reasons like better could mean
to be far more reliable in use or a better
range of tones and many other possible,
undefined criteria.
This could be down to a personal thing, but
generally most top guitar players will use
valve as a better sound. Even the term
‘valve’ is misleading, because they are
NOVEMBER ‘08 29
used in very different ways, in different
designs. As the name states, a valve really
does regulate a flow in a valve amp, but it’s
a flow of electrons, not water. Inside the
valve is a cathode and a plate, with a grid
in between. Electrons flow from the cathode
to the plate. The grid in between controls
the flow of electrons, hence the
valve-like action. The cathode has to be
warmed for this to happen, so there is a
small heater at the bottom of each valve.
This is what you are turning on when you
put the amp into standby. Very small voltages
applied to the grid cause big changes
in the electron flow (current) between the
cathode and the plate, that’s amplification.
The voltages are determined by a variable
input, an electric guitar! You might assume
that when you’re not playing at all, the grid
is at ov but this is not so. In a power valve,
it is likely to be somewhere around - 40v.
The precise voltage used varies from case
to case and is called the ‘bias setting’.
In a Class A circuit, the valve is never idle.
The bias is set so that the valve is passing
current at all times. The first known class A
guitar amp is the Vox AC15, introduced in
1956. Class B amps can produce a lot
more power than class A. They use two
power valves in a push pull configuration or
multiples of these pairs for higher powered
configurations. One of the pair handles the
positive side of the wave form, while the
other handle the negative. The bias is set
so that the valve is idle in between times.
In reality, this arrangement doesn’t sound
so good because there is unwanted distortion
of the waveform at the crossover point
where one valve stops working and the
opposite half of the pair kicks into life.
We will continue next month, meanwhile if
you are looking to purchase a new amplifier
remember guitars do have a sound of
their own, take your guitar with you when
buying a new amp, for you could try out in
the shop using one of theirs, get home and
find you are not satisfied with the sound!!
A good music shop will want you to buy
what you are looking for, since there is the
repeat business, of strings etc.....