Innovation. Amplified.
Chapter 6
Standby…...For
the Truth
by
Hartley Peavey
by rapid combination with oxygen in the air. By eliminating the presence of oxygen, the Tungsten filamen
heated to the point that light was produced (incandescence) thus, creating the “light bulb.” Early light bulb
clear glass and were fairly reliable, but tended to suffer from a blackening effect on the inside of the glass
considerable number of hours of operation. Edison and his team tried many different methods to eliminat
internal “blackening” effect without a lot of success.
Standby…… for the Truth
Incredibly, very few modern technicians (and even
fewer players) understand why so-called “standby”
switches have been placed on guitar amplifiers for
many decades. Almost every player believes that the
standby switch is provided on their amps to put the amp
in “standby mode” while they take a break, so that when
they flip the switch back on, the amp will be instantly
playable. The truth is that’s NOT the original purpose
Standby……
Truth
of a standby switch.
In orderfortothe
fully
understand the
problems
and
virtues
of
utilizing
a
standby
switch, why
oneso-called “standby”
Incredibly, very few modern technicians (and even fewer players) understand
needs
to
understand
a
little
about
how
vacuum
tubes
ches have been placed on guitar amplifiers for many decades. Almost every player believes that the standby
Knowledge
about
tubes
wasso that when they flip the Light bulb with added Electrode
ch is provided onactually
their ampswork.
to put the
amp in “standby
mode”vacuum
while they take
a break,
ch back on, the amp
be instantly playable.
truth
is that’s
the in
original
purpose of a standby switch. Light bulb with added Electrode
fairlywillwidespread
in the The
30’s,
40’s
andNOT
even
the 50’s;
der to fully understand
the problems
and virtues
of utilizing a standby
one needs
but since
the advent
of transistor
amps switch,
(beginning
in to understand a little
ut how vacuum tubes actually work. Knowledge about vacuum tubes was fairly widespread
in the 30’s,
40’s
and
One
of the methods
tried
was
inserting
small metal
electrode
through
the side ofthe
the glass bulb
discovered
that
a acurrent
was
flowing
through
the early 60’s) much of the “in depth” knowledge
about
n in the 50’s; but since the advent of transistor amps (beginning in the early
60’s)
much
of
the
“in
depth”
connecting
that
electrode
to
a
source
of
positive
voltage.
Much
to
the
surprise
of
the
Edison
lab personne
vacuum from the heated filament to the electrode
vacuum
has
been “lost.”
wledge about vacuum
tubestubes
has been
“lost.”
in the side of the glass bulb. This phenomenon was
named “the Edison Effect” and marked the discovery
of what is generally known as “thermionic emission”
(which is the operational basis of most vacuum tubes).
This new two element “light bulb”/tube represented
the first “RECTIFIER,” since it had only two elements
(the filament/cathode and the positively charged plate/
anode). Electrons were able to move through the
vacuum from the negatively charged filament/cathode
to the positively charged plate/anode. Please note, the
flow of electrons (current) traveled in one direction;
i.e., from cathode to anode, NOT vice versa. Thus, the
“Vacuum Tube Rectifier” (diode) was born.
Most people know that Thomas Edison invented the
Once the so-called “Edison Effect” became widely
By eliminating the presence of oxygen, the Tungsten
filament could be heated to the point that light was
produced (incandescence) thus, creating the “light
bulb.” Early light bulbs featured clear glass and were
fairly reliable, but tended to suffer from a blackening
effect on the inside of the glass bulb after a considerable
number of hours of operation. Edison and his team
tried many different methods to eliminate this internal
“blackening” effect without a lot of success.
to VARIABLY CONTROL the flow of electrons…In
essence, to create a kind of “electronic valve.” Fleming
(in the UK) and DeForest (in the US) apparently
discovered (about the same time) that if a third element
was added to the tube, the flow of electrons could be
controlled by applying a variable negative voltage to
this third element, which is usually called a “grid.” In
the early 1900’s, DeForest filed a patent for a three
element vacuum tube that he called the “Audion,”
thus making possible amplification as we know it. The
British called this device a “VALVE” since that’s what it
DOES! The US called it a “TUBE,” since that’s what it
LOOKED LIKE! Both names are “correct!”
Most people know that Thomas Edison invented the so-called “electric light bulb.” He discovered, after
known, laboratories all over the world began
so-called
light
bulb.”
He discovered,
y thousands of “trial
and error”“electric
experiments,
that he
could create
light by heating aafter
Tungsten filament to
experimenting
many
thousands
of
“trial
and
error”
experiments,
that
andescence” in a vacuum. If the vacuum were not present, the white hot filament would instantaneously
vaporize with light bulbs with secondary
electrodes
anodes (or plates). Scientists on both
light
by heating
Tungsten
filament
to
apid combinationhe
withcould
oxygencreate
in the air.
By eliminating
the apresence
of oxygen,
the Tungsten
filament could called
be
ed to the point that
light
was
produced
(incandescence)
thus,
creating
the
“light
bulb.”
Early
light
bulbs
featured
sides
of
the
Atlantic
realized that if they could establish
“incandescence” in a vacuum. If the vacuum were not
r glass and werepresent,
fairly reliable,
but
tended
to
suffer
from
a
blackening
effect
on
the
inside
of
the
glass
bulb
after
a
a one way flow of electrons, this phenomenon would
the white hot filament would instantaneously
siderable number of hours of operation. Edison and his team tried many different methods to eliminate this
be even more useful if some method could be devised
vaporize
by
rapid
combination
with
oxygen
in
the
air.
nal “blackening” effect without a lot of success.
One of the methods tried was inserting a small metal
electrode through the side of the glass bulb and
connecting thatLight
electrode
to a Electrode
source of positive
bulb with added
voltage. Much to the surprise of the Edison lab
personnel, they
One of the methods tried was inserting a small metal electrode through the side of the glass bulb and
necting that electrode to a source of positive voltage. Much to the surprise of the Edison lab personnel, they
2
2
a third
wasthird
added
towhich
thewhich
tube,
the
flowcalled
ofcalled
electrons
could
by applying
a variable
negative
voltage
toelement
thistothird
element,
is usually
a a“grid.”
InInbe
the
early
DeForest
fileda apatent
patent
a three
voltage
this
element,
is usually
“grid.”
thecontrolled
early 1900’s,
1900’s,
DeForest
filed
forfor
a three
voltage
to this
third
element,
is the
usually
called athus
“grid.”
In thepossible
early 1900’s,
DeForestas
filed
patent
a British
three
element
vacuum
tube
that that
hewhich
called
“Audion,”
amplification
as
weaknow
know
The
British
element
vacuum
tube
he called
the
“Audion,”
thusmaking
making
possible
amplification
we
it. it.for
The
element
he since
called
thethat’s
“Audion,”
making
possible
amplification
as since
we
know
it. what
The
British
called
thisvacuum
device
atube
“VALVE”
that’s
what
it thus
DOES!
The
US
it a “TUBE,”
“TUBE,”
since
that’s
what
it LOOKED
called
this device
athat
“VALVE”
since
what
it DOES!
The
UScalled
called
that’s
it LOOKED
called
this Both
device
aare
“VALVE”
since that’s what it DOES! The US called it a “TUBE,” since that’s what it LOOKED
LIKE!
names
are “correct!”
LIKE!
Both
names
“correct!”
LIKE! Both names are “correct!”
Since the discovery Since
of the
“Edisonof the
Effect”
in ahas“two
element”
vacuum
the discovery
“Edisonand
Effect”the
and the discussed
electronic valvethe
(tube)fact
muchthat
progress
been made
in
Since
the
discovery
of
the
“Edison
Effect”
and
the
electronic
valve
(tube)
much
progress
has
been
made
in
electronic valve
(tube)
much
progress
has
been
tube,
current
(i.e.
the
flow
of
electrons)
flows
just
ONE
the Since
tubes (valves)
themselves,
as“Edison
well as Effect”
the associated
Thevalve
earliest
usemuch
for audio
amplification
was made
in longin
the discovery
ofasthewell
andcircuitry.
thecircuitry.
electronic
(tube)
progress
haswas
been
the
tubes
(valves)
themselves,
as
the
associated
The
earliest
use
for
audio
amplification
in
long
distance (valves)
telephony asthemselves,
“repeaters” for “longline”
amplifiers
operate
using “direct
current” (DC)
made in the
tubes
welluse.asObviously,
WAYaudio
(from
theuse
negatively
charged
cathode
thedistance
tubes
(valves)
themselves,
as for
well“longline”
as as
the associated
circuitry.
earliest
for audio
amplification
was
in long to the
asmeans
“repeaters”
use.
Obviously,
audiotoThe
amplifiers
operate
“direct
current”
(DC)
andcircuitry.
atelephony
convenient
of converting
thefor
AC
mains/line
voltage
direct charged
current
wasusing
necessary.
Above, creating
we
the associated
The
earliest
use
audio
positively
anode)
thus
distance
telephony
as “repeaters”
for “longline”
use. tube,
Obviously,
amplifiers
operate
usingjust
“direct
(DC)a vacuum
and discussed
a convenient
the ACvacuum
mains/line
voltage
to audio
directthecurrent
necessary.
wecurrent”
the means
fact thatofinconverting
a “two element”
current
(i.e.
flow ofwas
electrons)
flowsAbove,
ONE
WAY (from
amplification
was
in
long
distance
telephony
as
tube
diode
that
today
we
call
a
“RECTIFIER.”
Because
and
athe
convenient
converting
thevacuum
AC mains/line
voltage
to
direct
wasflows
necessary.
Above,
wewe
discussed
the factmeans
that in of
a cathode
“two
element”
tube,
current
(i.e. the
flow
ofcurrent
electrons)
justdiode
ONEthat
WAY
(from
negatively
charged
to the
positively
charged
anode)
thus
creating
a vacuum
tube
today
discussed
the
fact
that incathode
a “twotoelement”
vacuum
tube,anode)
current
(i.e.creating
the
flow
ofcharacteristics
electrons)
flows
just
ONE
WAY
(fromthey were
“repeaters”
use.
Obviously,
audio
of
the
unique
oftoday
these
thefor
negatively
charged
the
positively
charged
athey
vacuum
diode
that
we
call a“longline”
“RECTIFIER.”
Because
of the
unique
characteristics
ofthus
these
tubes,
were tube
almost
universally
used
totubes,
call
a “RECTIFIER.”
Because
oftothethe
unique
characteristics
of
these
tubes,
theylater.
were
almost
universally
used
negatively
charged
cathode
positively
charged
anode)
creating
a vacuum
tube
thattotoday
weDC until the
amplifiers the
operate
using
“direct
and
almost
universally
used
to diode
convert
AC to
convert
AC
to DC
until
thecurrent”
invention
of(DC)
the
solid
stateadiode
manythus
decades
AC of
to DC
until
the invention
the solid
state diode many
decades
later.
a “RECTIFIER.”
Because
ofthe
theofunique
characteristics
ofinvention
these
tubes,
used to
convenientcallconvert
means
converting
AC
mains/line
of they
the were
solidalmost
stateuniversally
diode many
decades later.
convert
AC
to
DC
until
the
invention
of
the
solid
state
diode
many
decades
later.
voltage to direct current was necessary. Above, we
3
3
3
It is importantIt istoimportant
understand
at least
basic
first)inside
variety
of vacuum
tube
rectifiers utilized
to understand
at least the
the basic
process(and
that occurs
the vacuum
tube when
the cathode
tube/valve
“mechanics,”
should know“directly
that there are
a numbercathodes.”
of different
processemits
thatelectrons.
occurs Before
insidediscussing
the vacuum
tube
when youso-called
heated
Essentially,
configurations
of vacuum tube
rectifiers.
As far as audio
are cathodes
concerned, we
need
be aware
of just twoversions of the
the cathode
emits electrons.
Before
discussing
tube/amplifiers
these
are
merely
modified
basic types. Theyou
simplest
(and first)
variety
vacuumare
tube rectifiers
utilizedfilaments
so-called “directly
heated cathodes.”
valve “mechanics,”
should
know
thatof there
Tungsten
themselves,
having no additional
Essentially,
these
cathodes
are
merely
modified
versions
of
the
Tungsten
filaments
themselves,
having noitself,
additional
a number of different configurations of vacuum tube
structure other than the “heater”
usually being
structure other than the “heater” itself, usually being treated with some kind of “emissive” coating. The first heater
rectifiers. As far as audio amplifiers are concerned, we
treated with some kind of “emissive” coating. The
cathodes were pure Tungsten, which were less than “ideal” as a cathode. Further research into the chemistry of
need becathode
awarematerials
of justproduced
two basic
types.
first which
heater
cathodes
were
pure Tungsten, which
a cathode
thatThe
wassimplest
treated with thorium,
reduced
the optimum
operating
3
temperature by about 1,000 °F. Unfortunately, Thoriated Tungsten
is extremely brittle and sensitive to shock;
therefore, later research indicated that a tungsten filament coated with barium and/or strontium oxide, not only
were less than “ideal” as a cathode. Further research
into the chemistry of cathode materials produced a
cathode that was treated with thorium, which reduced
the optimum operating temperature by about 1,000
°F. Unfortunately, Thoriated Tungsten is extremely
brittle and sensitive to shock; therefore, later research
indicated that a tungsten filament coated with barium
and/or strontium oxide, not only enabled substantially
lower operating temperatures, but also increased
emission of electrons. Later calcium carbonate was
added to this coating to stabilize the tube’s operation
by minimizing another internal problem to the tube
called “secondary emission (which is another tube
amp phenomenon beyond the scope of this paper).
ortant to understand at least the basic process that occurs inside the vacuum tube when the cathode
Tube Type Rectifiers
Before discussing tube/valve “mechanics,” you should know that there are a number ofRecognizing
different the problem with rectifiers that delivered the high B+ voltages almost instantaneously, tube
designers developed
“INDIRECTLY
HEATED”iscathode
rectifiers which delayed
AVAILIBILITY
The early
used “directly
heated
cathodes”
cathode
rectifier
presently
the 5AR4/GZ34.
This
tube of full high
vacuum tube rectifiers.
As farrectifiers
as audio amplifiers
are concerned,
we need
be aware
of
just
twonumerous
voltage since the cathodes of these rectifiers often had relatively slow (controlled) warm up time. In audio
(which
themselves,
merely
heater
filaments
has
a controlled
up time
designed
simplest (and first)
varietywere
of vacuum
tube rectifiers
utilizedthe
so-called
“directly
heated
cathodes.”
amplification,
the most
popular indirectlywarm
heated cathode
rectifierespecially
presently is the 5AR4/GZ34.
Thisto
tube has a
controlled
warm
up timethe
especially
designed
match of
the warm
time of indirectly
the other indirectly
heated cathode tubes
cathodes are merely
modified
of the Tungstenoxide).
filamentsThey
themselves,
having no
additional
coated
with aversions
barium/strontium
produced
match
warm
up totime
the up
other
heated
in an amp. Fortunately, the 5AR4/GZ34 is readily available and (in most instances) can replace the venerable 5U4
an the “heater” itself,
usually
being VERY
treated RAPIDLY
with some kind
of “emissive”
The firstcases
heater
output
voltage
when
turned coating.
on. Since
in an3 amp.
Fortunately,
the
5AR4/GZ34
and in somecathode
(wheretubes
there’s adequate
amp heater
current) the smaller
(2 amp)
5Y3. An additional benefit o
re Tungsten, which
were
less
than
“ideal”
as
a
cathode.
Further
research
into
the
chemistry
of
indirectly
heated
cathode
rectifiers
is
that
they
are
usually
more
efficient,
while
at
the
samereplace
time providing less
these directly heated cathodes were often used to is readily available and (in most instances) can
voltage
drop across the tube because of its more efficient design. Using these “controlled warm up tube” rectifiers,
produced a cathode
that
was
treated
with
thorium,
which
reduced
the
optimum
operating
power other tubes (valves) whose cathodes were
thenegates
venerable
5U4
andswitch
in some
cases
(where
there’s
a major
the need for
a “standby”
because their
controlled
warm up time
accomplishes (more
bout 1,000 °F. Unfortunately, Thoriated Tungsten is extremely brittle and sensitive
todegree,
shock;
or full
less) the adequate
same thing (automatically)
thatheater
a “standbycurrent)
switch” is SUPPOSED
to do. Most(2
modern
audio amps using
“INDIRECTLY
HEATED,”
a
problem
arose
when
the
3
amp
the
smaller
amp)
Tube
Type
Rectifiers
search indicated that a tungsten filament coated with barium and/or strontium oxide,
not
only utilize (or should) a controlled warm up rectifier such as the 5AR4/GZ34.
tube type
rectifiers
platetemperatures,
voltage (B+)
appliedemission
BEFORE
the “indirectly
5Y3. An additional benefit of indirectly heated cathode
ally lower operating
but was
also increased
of electrons.
Later calcium
Recognizing
the problem
with is
rectifiers
that delivered
the highmore
B+ voltages
almostwhile
instantaneously,
tube
heated”
cathodes
of the
audiobyamplifier’s
tubes
reached
rectifiers
that they
are usually
efficient,
at
ded to this coating
to stabilize
the tube’s
operation
minimizing another
internal problem
to the
developed
cathode
which
delayed
AVAILIBILITY
temperature.
Whenbeyond
thedesigners
full
voltage
the “INDIRECTLY
same time HEATED”
providing
lessrectifiers
voltage
drop
across
the of full h
ndary emission their
(whichoperating
is another tube
amp phenomenon
thehigh
scope
of thisnumerous
paper).
since the cathodes of these rectifiers often had relatively slow (controlled) warm up time. In audio
(B+) is applied significantly BEFOREvoltage
a tube
reaches tube because of its more efficient design. Using these
amplification, the most popular indirectly heated cathode rectifier presently is the 5AR4/GZ34. This tube has a
y rectifiers usedoperating
“directly heated
cathodes”
(which
were
themselves,
merely
the
heater
filaments
temperature, the cathodecontrolled
coatingwarm
can
be especially
“controlled
warm
upthe
tube”
toother
a major
degree,
up time
designed
to match
warmrectifiers,
up time of the
indirectly
heated cathode tu
um/strontium oxide).
They
produced
output
voltage
VERY
RAPIDLY
when
turned
on.
Since
thesethe
“stripped” of its ability to emit electrons.
This
destructive
needavailable
for a “standby”
switch because
in an
amp.
Fortunately, thenegates
5AR4/GZ34
is readily
and (in most instances)
can replacetheir
the venerable 5
thodes were often
used tois
power
other“cathode
tubes (valves)
whose cathodes
“INDIRECTLY
and
in some
(where there’s
adequate
3 ampup
heater
current)
the smaller (2 amp)
5Y3.orAnless)
additional bene
process
called
stripping”
and
itwere
iscases
mainly
controlled
warm
time
accomplishes
(more
lem arose when the full plate voltage (B+) was applied BEFORE
the “indirectly
heated”rectifiers
cathodes
of they are usually more efficient, while at the same time providing less
indirectly
heated
cathode
is
that
for THIS REASON that socalled “standby”
switches
the same thing (automatically) that a “standby switch”
r’s tubes reached their operating temperature. When the full high
voltage
is the
applied
voltage
drop (B+)
across
tube because of its more efficient design. Using these “controlled warm up tube” rectifie
were
provided
on
numerous
electronic
devices
using
SUPPOSED
to do. Most modern audio amps using
ORE a tube reaches operating temperature, the cathode coating
can be
“stripped”
of itstheis
ability
a major
degree,
negates
need to
for a “standby” switch because their controlled warm up time accomplishes (m
DIRECTLY
HEATED
RECTIFIERS
(with
INDIRECTLY
tube
type
rectifiers
should) atocontrolled
warm
his destructive process is called “cathode stripping” and it is mainly
forthe
THIS
REASON
that so- that a “standbyutilize
or less)
same
thing (automatically)
switch”(or
is SUPPOSED
do. Most modern
audio amps u
HEATED
TUBES for
operation)!
rectifier
such warm
as the
5AR4/GZ34.
tube type rectifiers
utilize
(orup
should)
a controlled
up rectifier
such as the 5AR4/GZ34.
witches were provided
on numerous
electronic
devices using DIRECTLY
HEATED
RECTIFIERS
Y HEATED TUBES for operation)!
4
Recognizing the problem with rectifiers that delivered
the high B+ voltages almost instantaneously, tube designers developed numerous “INDIRECTLY HEATED”
cathode rectifiers which delayed AVAILIBILITY of full
high voltage since the cathodes of these rectifiers often
had relatively slow (controlled) warm up time. In audio
amplification, the most popular indirectly heated
4
strument amplifiers. In many cases, these so-called
“standby” switches are provided only because they are
“expected” to be there. One should always be aware
that the REAL reason the standby switch is provided is
to switch OFF the high voltage (B+) UNTIL the tubes
reach their FULL OPERATING TEMPRATURE, so as to
avoid “cathode stripping” of the indirectly heated cathodes of the preamp and output tubes.
Peavey provides an “AUTOMATIC STANDBY FEATURE” on most of its tube amps through the use of
what are called “inrush current limiters.” These are devices having a “reverse temperature coefficient,” i.e.
they have substantial resistance when COLD and alIt should be noted
that
some ampthat
designers
and musicians
prefer
using the technically
inferior
direct heated most no resistance after they WARM UP! When these
It
should
be
noted
some
amp
designers
and
musicathode rectifiers because of their less efficient operation, as compared to more modern types such as the
GZ34/5AR4
or the
smaller GZ-81
indirectlythe
heated
cathode rectifiers. The
older rectifiers,
such as heated
the 5Y3, 5U4, 5R4, devices are inserted 7 into the power supply, they prescians
prefer
using
technically
inferior
direct
etc, etc. have a higher voltage drop, resulting in less B+ and have a more pronounced tendency to “sag” under load.
ofcertain
their
less
operaSomecathode
players and amprectifiers
designers believebecause
this is desirable for
playing
styles.efficient
The more modern
tube rectifiers ent a resistance to the “inrush” of current to the power
are more efficient, have less voltage drop, better regulation (less sag) as well as providing the tube longevity benefits
tion,
as
compared
to
more
modern
types
such
as
the
supply, thus considerably SLOWING down the “warm
of their controlled warm up. In spite of the above, you will sometimes see modern amplifiers designed with
the
cheaper
and less efficient directly
heated
typessmaller
of tube rectifiersGZ-81
such as the 5Y3
and 5U4. It is myheated
opinion that if
GZ34/5AR4
or
the
indirectly
up” process and allowing the tubes to reach their optube rectifiers are to be used, the more modern and efficient indirectly heated types are the FAR better choice (and in
most cathode
cases provide a direct
replacement).
A
word
of
caution
is
in
order,
the
two
amp
heater
rating
of
the
5Y3
has
rectifiers. The older rectifiers, such as the 5Y3, erating temperature BEFORE the full high voltage (B+)
sometimes been a limitation in replacing that particular tube with the GZ34/5AR4, since the latter’s heater current
5U4,are5R4,
etc.(3 amp)
have
is applied to the plates. This can be thought of as a
requirements
the sameetc,
as the larger
5U4. a higher voltage drop, resulting
in
less
B+
and
have
a
more
pronounced
tendency
Most musicians WRONGLY assume that the standby switch is provided primarily to disable the amplifier in kind of “automatic standby switch.” Most Peavey tube
such to
a way“sag”
as to provide
instantaneous
operation
by switching
on the “standby”
Some
even refer to this
under
load.
Some
players
andswitch.
amp
designers
amps utilize these “inrush current limiters” (whether the
switch as a “beer button” to cut off the amp during breaks in a performance. Unfortunately, this very widely held
MISCONCEPTION
(and is
does)desirable
cause problems. The
of these problems
should be
understoodThe
if one
believe can
this
fornature
certain
playing
styles.
amp features a standby switch or not). We do that as
wants to maintain optimum tube life and performance for as long as possible.
more modern tube rectifiers are more efficient, have a safety factor simply because most players have no
As stated above, standby switches have more or less become an “expected feature” of modern tube
less
voltage
drop,
better
sag)
as well
idea what the standby switch is actually for. Hopefully,
instrument
amplifiers.
In many
cases, these
so-calledregulation
“standby” switches (less
are provided
only because
they areas
into the power supply, they present a resistance to the “inrush” of current to the power supply, thus considerably
“expected”
to
be
there.
One
should
always
be
aware
that
the
REAL
reason
the
standby
switch
is
provided
is
to
providing the tube longevity benefits of their controlled the
above
sheds
some
real temperature
purpose
SLOWING
down the “warm
up” process
and allowinglight
the tubes on
to reachthe
their operating
BEFOREand
the full
switch OFF the high voltage (B+) UNTIL the tubes reach their FULL OPERATING TEMPRATURE, so as to avoid
high voltage (B+) is applied to the plates. This can be thought of as a kind of “automatic standby switch.” Most
“cathode
stripping”
of theIn
indirectly
heated
of the preamp you
and output
tubes.
warm
up.
spite
ofcathodes
the above,
will
sometimes see proper
use
the
switch
Peavey tube amps
utilizeof
these
“inrushstandby
current limiters” (whether
the amp features a standby switch or not). We do
that as a safety factor simply because most players have no idea what the standby switch is actually for. Hopefully,
modern
amplifiers
designed
with
theof cheaper
and
Peavey provides
an “AUTOMATIC
STANDBY FEATURE”
on most
its tube amps through
the less
use of what the above sheds some light on the real purpose and proper use of the standby switch.
are called “inrush current limiters.” These are devices having a “reverse temperature coefficient,” i.e. they have
efficient
heated
typesafteroftheytube
rectifiers
suchareas
substantial
resistancedirectly
when COLD and
almost no resistance
WARM UP!
When these devices
inserted
the 5Y3 and 5U4. It is my opinion that if tube rectifiers 6
are to be used, the more modern and efficient indirectly heated types are the FAR better choice (and in most
cases provide a direct replacement). A word of caution
is in order, the two amp heater rating of the 5Y3 has
sometimes been a limitation in replacing that particular
tube with the GZ34/5AR4, since the latter’s heater current requirements are the same as the larger (3 amp)
Above, we mentioned the concept of “cathode stripping,” which can occur when the full high voltage supply
is applied to the anode (plate) of a tube BEFORE its heater/cathode reaches normal operating temperature. The
5U4.
Above,
we this
mentioned
the
of be“cathode
mechanism that causes
is often not understood,
but anyconcept
tube amp user should
aware that electronsstripare
emitted from the cathode in basically a “two step” process. As the cathode is heated to incandescence (i.e. turns
ping,”
which can occur when the full high voltage supred) a small “cloud” of electrons develops around the cathode itself. These electrons literally “boil” off the cathode
material into the space around it, and this is known as “space charge.” Ideally, electrons are attracted to the anode
Most musicians WRONGLY assume that the standby ply
is applied to the anode (plate) of a tube BEFORE
(plate) from this “cloud,” as opposed to directly from the cathode material itself. When the cathode has not reached
its proper
operating temperature (i.e. thereaches
cathode is not yetnormal
incandescent/glowing)
electrons are “ripped”
from the
switch is provided primarily to disable the amplifier in its
heater/cathode
operating
temperabarium/strontium/calcium carbonate cathode coating itself, causing a phenomenon known as “cathode stripping.”
The
standby
switch
was
provided
to
allow
the
tubes
to
reach
their
full
operating
temperature
(thus,
establishing
the
such a way as to provide instantaneous operation by ture.
The mechanism that causes this is often not un“space charge” around the cathode) BEFORE the high voltage is applied to the plates.
switching on the “standby” switch. Some even refer to derstood,
but any tube amp user should be aware that
While the above is fairly simple and basic explanation, one should also be aware that EXCESSIVE USE of a
standby switch can cause
destructive process
withinthe
the tube.
If the tubes in thein
amp basically
are allowed to operate
this switch as a “beer button” to cut off the amp dur- electrons
areanother
emitted
from
cathode
a
for considerable lengths of time with the standby switch off (no B+/high voltage) the cathode material itself tends to
build up a destructive
within itself, and
is referred
to as “cathode poisoning.”
The “old to
timers”
used to
ing breaks in a performance. Unfortunately, this very “two
step”process
process.
Asthisthe
cathode
is heated
incancall this phenomenon “SLEEPING SICKNESS!” When a tube is at full operating temperature and no current is being
drawn (as is the case with
no B+/high
voltage)red)
a high resistance
layer is gradually
formed atof
the “interface”
between
widely held MISCONCEPTION can (and does) cause descence
(i.e.
turns
a small
“cloud”
electrons
the oxide coating and the nickel cathode structure. This layer of barium orthosilicate causes tube performance to
problems. The nature of these problems should be develops
cathode
electrons
degrade significantly. around
It is important thatthe
the standby
switch NOT be itself.
left in the “offThese
position” (no B+)
for more than 15
to 20 minutes at a time to avoid “poisoning” the tube’s cathodes.
understood if one wants to maintain optimum tube life literally “boil” off the cathode material into the space
Ideally (in the standby mode) a tube should be operated with REDUCED heater current AND REDUCED
and performance for as long as possible.
around
it, and
is known
as “space
charge.”
plate voltage (instead
of FULL this
heater current
and NO plate voltage).
I know of no instrument
amp thatIdeally,
has ever used
this expensive technique.
electrons
are attracted to the anode (plate) from this
In addition to the current inrush limiters, Peavey utilizes a somewhat different approach to standby
As stated above, standby switches have more or less “cloud,”
ascurrent
opposed
to directly
from
cathode
mateoperation. The inrush
limiters help protect
the amplifier at turn
on (coldthe
start) but
conventional standby
switches (that remove the B+ from the plates) can cause poisoning of the cathode, which can rapidly damage tube
become an “expected feature” of modern tube in- rial
itself.
When
cathode
hasgridsnot
itsshuts
proper
performance.
We have
found thatthe
disabling
voltage to the screen
of the reached
output tubes effectively
the tube
operation down to a major degree yet (by retaining full voltage on the plates) allows current to continue to flow albeit
at a greatly reduced rate. This “standby” technique effectively prevents so-called “sleeping sickness”/cathode
5
7
operating temperature (i.e. the cathode is not yet incandescent/glowing) electrons are “ripped” from the
barium/strontium/calcium carbonate cathode coating
itself, causing a phenomenon known as “cathode stripping.” The standby switch was provided to allow the
tubes to reach their full operating temperature (thus,
establishing the “space charge” around the cathode)
BEFORE the high voltage is applied to the plates.
Given that the true purpose of a standby switch is generally not understood, and the fact that the improper
operation of the standby switch can cause problems
when EITHER ON or OFF, I feel it is vital that the player
understand the true purpose of a standby switch. However, the player also needs to understand the problems
that can occur when the standby switch is used improperly, causing the aforementioned “cathode stripping” on one hand, and “cathode poisoning” on the
other hand, both of which can (and often do) cause
tubes to fail prematurely.
While the above is fairly simple and basic explanation,
one should also be aware that EXCESSIVE USE of a
standby switch can cause another destructive process
within the tube. If the tubes in the amp are allowed
to operate for considerable lengths of time with the
standby switch off (no B+/high voltage) the cathode
material itself tends to build up a destructive process
within itself, and this is referred to as “cathode poisoning.” The “old timers” used to call this phenomenon
“SLEEPING SICKNESS!” When a tube is at full operating temperature and no current is being drawn (as is
the case with no B+/high voltage) a high resistance
layer is gradually formed at the “interface” between the
oxide coating and the nickel cathode structure. This
layer of barium orthosilicate causes tube performance
to degrade significantly. It is important that the standby
switch NOT be left in the “off position” (no B+) for more
than 15 to 20 minutes at a time to avoid “poisoning” the
tube’s cathodes.
Even though it is “counterintuitive,” ideally the standby
switch should be eliminated through the use of some
kind of AUTOMATIC device that slows up the turn on
process and allows the tube heaters and the associated cathodes to reach full operating temperature BEFORE the full high voltage (B+) is applied. We have
found that “inrush current limiters” operate perfectly
in this role, have no moving parts, and thus very effectively optimize tube life in an amplifier. This is why
Peavey uses “inrush current limiters” in most of its
tube amps (whether a standby switch is incorporated
of not). These devices can be considered “automatic
standby switches,” providing the maximum protection
to the tubes. Almost as good is the usage of controlled
warm up rectifiers such as the 5AR4/GZ34.
Hopefully the above will “shed some light” on the single
most misunderstood feature of tube guitar amps.
More information about this is available on Peavey’s
website and on “PVTV.”
Ideally (in the standby mode) a tube should be operated with REDUCED heater current AND REDUCED
plate voltage (instead of FULL heater current and NO
plate voltage). I know of no instrument amp that has
ever used this expensive technique.
In addition to the current inrush limiters, Peavey utilizes
a somewhat different approach to standby operation.
The inrush current limiters help protect the amplifier at
turn on (cold start) but conventional standby switches
(that remove the B+ from the plates) can cause poisoning of the cathode, which can rapidly damage tube
performance. We have found that disabling voltage to
the screen grids of the output tubes effectively shuts the
tube operation down to a major degree yet (by retaining full voltage on the plates) allows current to continue
to flow albeit at a greatly reduced rate. This “standby”
technique effectively prevents so-called “sleeping sickness”/cathode.
poisoning if the standby switch is accidentally left on
for an extended period. This method also reduces
stress and arcing in the standby switch itself because
of the reduced current draw of the screens of the tubes/
valves.
6
7
Innovation. Amplified.
Peavey Electronics Corporation • 5022 Hartley Peavey Drive • Meridian, MS 39305
Phone: (601) 483-5365 • Fax: (601) 486-1278 • www.peavey.com • ©2006 Printed in the U.S.A.