Oestex ©
GUITAR
AMPS PAGE
SECTION 4: THE VACUUM TUBE - also known as “ELECTRON TUBE”
or “TUBE”.
In European countries including the UK, Australia and New Zealand,
the Vacuum Tube is known as a “VALVE” or “Radio Valve”.
The vacuum tube is to an amplifier as the
carburettor is to a motor vehicle engine.
If there is no input regulating device, an
engine will simply run at full RPM and power output - usually to
self-destruction, so the carburettor serves to regulate fuel/air gas mixture
and flow into the engine as a means of regulating engine power output.
By means of controlling carburettor
operation, the driver determines the speed at which the engine operates - to
produce power for transmission through the drive train to the driving wheels.
Similarly, the vacuum tube is an
electro-mechanical electronic regulating device that uses a small input effort
to produce a comparatively large output power.
Just as we would not claim the butterfly
valve in a carburettor produces the engine power output we would not also claim
the input signal voltage to a vacuum tube produces the amplifier power output.
Importantly, the vacuum tube, like the
carburettor neither produces power nor consumes it (excepting for heating
requirements and efficiency losses).
PRIMARY FUNCTIONS OF THE VACUUM TUBE IN A GUITAR AMPLIFIER
In considering ELECTRIC GUITAR audio amplifier design principles, it is first
vital to understand the vacuum tube serves three fundamental purposes or
functions:
1. RECTIFICATION
2. PRE-AMPLIFIER – VOLTAGE AMPLIFIERS, PHASE
SPLITTING/INVERSION AND SIGNAL DRIVE POWER TO POWER TUBES
3. POWER AMPLIFIER
FIRST PRIMARY FUNCTION:
AC TO DC RECTIFICATION
RECTIFICATION
A tube or solid state audio
amplifier operates by (DC) direct
current. This is the same form of electrical energy that powers a motor
vehicle or flashlight or portable radio.
But electrical energy
supplied from the power grid is in a different form – being (AC) alternating current.
So it is necessary to
convert the mains AC alternating current
power to DC direct current to enable
the amplifier tubes to function.
In addition, the DC voltage required to operate power
tubes is usually significantly higher than the mains AC voltage input.
So both voltage and current undergo
change.
The section of the amplifier
that does this is called the Power
Supply.
The process of changing the form of the energy is called Rectification. It follows that tubes
used for this function are called Rectifiers.
The Power Supply includes a Mains
Power Plug and lead (or DIN socket), a Fuse, an On-Off switch, a Power
Transformer, a Tube Rectifier, one or more Filter Capacitors, and sometimes a
Filter Choke.
It is common practice to
include a small switching surge bypass capacitor across the mains input to
bypass switching spikes.
Vacuum Tubes require to be
internally self-heated so the energy for heating is taken directly from the
Power Transformer via dedicated low voltage secondary windings.
Tubes used in the Power
Supply section must be supplied from windings independent to windings provided
for power tubes, driver tubes and pre-amplifier tubes.
Sometimes to eliminate hum
in the Preamp section of an amplifier it is necessary to also use DC Direct
Current for heating preamp tubes.
RECTIFIER CIRCUIT SECTION OF THE
AMPLIFIER’S POWER SUPPLY:
If a tube rectifier
is installed, its function is to convert alternating current (AC) supplied from
the power (mains) ISOLATING transformer secondary winding to direct current
(DC), which is necessary for the power and voltage amplifier tubes to operate.
A FULL WAVE rectifier tube is the only practical option.
For details as
to how this process works see HOW
TO DESIGN AND CONSTRUCT A HIGH
QUALITY POWER SUPPLY FOR AN AUDIO AMPLIFIER USING ELECTRON TUBES at https://www.oestex.com/tubes/power.html
The rectifier tube does not amplify but acts
as a semi-conductor, allowing AC current to pass forwards into the amplifier
but blocks reverse current – i.e. conducts in a forwards direction only.
Some amplifiers use
two full-wave rectifier tubes operating in parallel to deliver more current and
less voltage sag under load current as amplifier power output increases.
Important design elements to watch are:
DIRECTLY
HEATED RECTIFIERS (i.e. a tube having
a combined filament heater/cathode) such as 5AS4, 5R4, 5U4GB, 5Y3GT, 5Z3, 5V4,
6X4, supplying capacitor input filters
produce a peak DC voltage output waveform approximately 1.4 x the rms input
voltage at switch-on, slowly reducing as the amplifier progressively draws
current and settles into its steady state operating condition. Consequently the
first capacitor following the rectifier MUST have a surge rating of at least
1.5 x the rms transformer voltage.
Another option is to use an INDIRECTLY HEATED RECTIFIER tube – i.e.
a tube having a separate heater and cathode instead of a filament. Examples are
GZ32 and GZ34/5AR4. The advantage of this style of tube is that the DC output
voltage under load is higher than a Directly Heated unit. Also the heater
warmup time is slower, than the power tubes, thereby reducing the switch-on
surge voltage. In some situations the power tube warmup to conduction is slower
than the rectifier, resulting in a surge voltage being present until the
amplifier settles into its steady state operating condition
FILTERS:
CAPACITOR
INPUT FILTERS:
The 100 Hz ripple (hum) voltage present at
the output from the rectifier will produce a loud hum in the loudspeaker. This
is worse with single-ended output stages (i.e. one tube or parallel single
tubes) than push-pull paired tubes. Push-pull operation cancels out some – but
not all - of the ripple, so audible hum may still be present.
A Capacitor
Input Filter comprises a single electrolytic capacitor connected between B+
and ground.
The capacitance value of electrolytic filter
capacitors used with tube rectifiers is limited to about 40 uF for most and 100
uF for a few exceptions. The filter choke is better installed in the negative
supply – i.e. between the transformer CT and ground or between a FWB rectifier
negative terminal and ground.
The capacitance value of electrolytic filter
capacitors used with solid state FWB rectifiers can be as large as required –
e.g. 1,000 uF, however care must be taken to limit inrush charging current to a
safe value for the power transformer windings.
CHOKE
INPUT FILTERS
A PII filter will remove most of the hum but
requires a filter choke and a further capacitor, however for cost, space and
weight considerations many guitar amplifiers do not include a filter choke.
Some designs do instal a small filter choke to supply the driver and preamp
tubes where hum can be troublesome. A filter choke is recommended for
single-ended amplifiers.
In a push-pull amplifier with Fixed Bias to
the power tubes power supply hum can be reduced by careful balancing of power
tube bias, however amplifiers using Self-Bias or Cathode Bias systems
adjustment is not available so matched tubes may be the answer.
Choke
Input Filters produce less ripple
(hum) voltage but require a higher input voltage for any given DC output. Choke
Input Filters are not usually seen in guitar amplifiers due to the extra cost,
space and weight. The AC output voltage is typically 0.9 x the plate to plate
AC input voltage after the load settles into its steady state operating
condition. Note the electrolytic filter
capacitors must be capable of handling the initial switch-on surge voltage,
which will still be at least 1.4 x the AC input voltage. The capacitance value
of electrolytic filter capacitors used with tube rectifiers is limited to about
40 uF for most and 100 uF for a few exceptions. The filter choke is better
installed in the negative supply – i.e. between the transformer CT and ground
or between a FWB rectifier negative terminal and ground.
The capacitance value of electrolytic filter
capacitors used with tube rectifiers is limited to about 40 uF for most and 100
uF for a few exceptions. The filter choke is better installed in the negative
supply – i.e. between the transformer CT and ground or between a FWB rectifier
negative terminal and ground.
IMPORTANT: If a standby-switch is included to isolate the B+
supply to the power tubes, it is the case that until the power tubes are connected
to the rectifier output all surge voltages will appear across any filter
capacitors between the rectifier terminal and the switch and remain until the
power tubes conduct – such as during band breaks. It follows that the filter
caps must have adequate DC WORKING voltage rating that equals or exceeds the
surge voltage.
An alternative method is to switch the AC HV
supply between the transformer secondary and the rectifier tube.
SOLID
STATE RECTIFIERS
SOLID STATE RECTIFIERS may be used to replace tube rectifiers. Solid state FULL WAVE BRIDGE rectifiers offer many
advantages, including virtually no losses to B+ voltage under load, low
under-chassis physical space requirements, low cost, low heat and most
importantly, their ability to handle very large values of filter capacitor to
reduce hum, improve voltage regulation and supply adequate current to the power
tubes when called upon. Despite these advantages, some guitarists do not like
the clean sound they deliver to the speaker so prefer the distorted power sag
characteristics produced by tube rectification.
DISTORTION
Where distortion
is deliberately required one of the easy ways to ensure it is to design in
voltage sag in the B+ supply - i.e. as the load current increases so the B+
voltage reduces – moreso than would otherwise occur.
Simple techniques based on the Power Supply
are:
·
use the lowest
filter capacitor value that will not cause unreasonable hum
·
limit the VA
rating of the power transformer to a safe minimum,
·
insert a 50 Ohms
wire wound resistor of suitable wattage value into the B+ supply,
·
insert a 50 Ohms
wire wound resistor of suitable wattage value between the transformer CT and
ground or between a FWB rectifier negative terminal and ground,
·
in fixed bias
output stages insert a 50 Ohms wire wound resistor between each power tube
socket cathode terminal and ground
·
in fixed bias
output stages adjust the bias as negatively as can be audibly tolerated – say
10 mA per tube, to shift operation into Class B. Note Class B operation
requires AC signal driving power from the previous stage to the grids of the
power tubes. The driving stage may not have adequate output for this mode so
adjust the bias until satisfactory performance is achieved.
·
minimise negative
feedback from the loudspeaker terminals
·
use a half-wave
voltage doubler power supply (is easy with solid state diodes but not practical
with tube rectifiers)
Other techniques are described elsewhere in
this website
CLEAN
SOUND
If a clean sound is required the electrolytic
capacitors in the power supply may be replaced by polypropylene motor start
capacitors. Note the DC rating is 1.4 x the AC rating.
POWER OUTPUT STAGE
The function of the vacuum POWER tube is
to electronically regulate the Direct Current (DC) flowing through it in such
manner that it varies in direct proportion to the applied ALTERNATING CURRENT
(AC) signal voltage. This is effected
by injecting the AC signal driving voltage into Grid #1 of the vacuum tube.
(Other Grids can be used but Grid #1 is the most common configuration).
It is the variable Direct Current flowing
in this circuit that, when applied into a LOAD produces the Alternating Current
OUTPUT via the output transformer into the loudspeaker -.
Thus the Alternating Current OUTPUT
applied into a LOAD produces the useable output from the amplifier.
To simplify our understanding, we could
regard the Power Supply Direct Current circuit as the SOURCE of power -
or INPUT POWER, and the Alternating Current circuit as the LOAD -
or OUTPUT POWER.
Hence the vacuum tube may be classed as a
TRANSDUCER because it converts energy from one form – i.e. Direct Current (DC)
to Alternating Current (AC). On the other hand, the complete Amplifier is not,
because it uses an AC input from the guitar pickups to produce an AC output to
the loudspeaker.
The resultant Alternating Current output
means that a single vacuum tube provides a common current path for BOTH
Direct Current and Alternating Current circuits.
In the case of the DC circuit, that portion
of the current path between Plate and Cathode terminals of the vacuum tube, is
used to REGULATE the DIRECT CURRENT flow in the whole circuit under constant
supply voltage conditions by means of the Control Grid (Grid #1). A negative DC
voltage (Grid Bias) is applied to it so that it will present a negatively
charged element that controls the current flow to the desired level by
interfering - in a deliberately controlled manner - with the ability of the
Plate to attract electrons from the Cathode.
Because the vacuum tube has negligible
internal DC resistance or AC impedance (see tube rectifier characteristics for
typical values) and it is a current path in the circuit supplied by the Power
Supply, it is essential to insert a LOAD into the circuit to limit total current
to acceptable limits - otherwise the tube would behave as a low-resistance
metallic conductor.
The second primary function of the vacuum
POWER tube is to provide a current path for the load on the power supply source
input power - which is in DIRECT CURRENT form.
Without a return path no current will flow in
the power source circuit. That is to say, current can only flow in the circuit
when the vacuum tube conducts.
This is demonstrated by the fact that if the
power supply voltage is applied to the Cathode and Plate terminals of a cold
vacuum tube, current will not flow. However if a fixed resistor - having the
same resistance value as that specified for the design value of AC load
impedance for the particular power output vacuum tube(s) - is inserted
into the circuit in series with the vacuum tube and the tube terminals bridged
with a wire conductor, then DC current will flow to a value determined by the
resistor.
In the case of a Plate loaded output
transformer configuration, the output AC circuit load also is shared with the
DC circuit - i.e. is common to both circuits. This is achieved by installing
the LOAD in series with the Tube Plate and Cathode terminals.
The value of the DC power so consumed by the
circuit will be equivalent to the maximum AC power output plus circuit losses.
Fundamental to amplifier design is the
principle that maximum power output of an amplifier is limited to the "prospective
power" of the power supply - i.e. the maximum power (Volts x Amperes)
the power supply can deliver in any instant of time into its load.
Actual maximum signal power output (including any distorted component) cannot exceed the
"prospective power" capability less circuit losses. Circuit losses
are always very significant, even at audio frequencies, ranging from about 23%
minimum to about 70% of power supply DC input power.
Thus what is of most significance to us is
that assuming a constant value of load in the circuit, Actual amplifier
power output is regulated by the vacuum tubes in the circuit - not by its load.
Another important concept to understand is
that electron flow in vacuum power tubes does not operate in quite the same way
as in the electroplating process. In that process using Direct Current,
particles of a metal material are transferred from the Cathode to the solution,
thence to the Anode - which is the article being electroplated. The Cathode
metal is consumed by the process and eventually there is none left.
However in a vacuum tube this process does
not occur - i.e. during normal tube operation significant amounts of
Cathode material do not deposit onto the Plate. This tells us that the electron
flow in a vacuum tube may be nothing more than a static stream of conductive
particles that assemble in the tube to bridge the Cathode to the Anode (Plate).
Hence, the performance and "sound"
of an audio amplifier should be far more dependent upon circuit design and
componentry than what goes on in the vacuum tube itself.
Practical experience though tells us
differently and there is provable difference in sound between different tube
types.
SELECT THE TUBE COMPLEMENT
This is also a very crucial step in the
design process.
The choice of tubes is very large, however in
practice, there are only a few types that have demonstrated over time that they
are worthy to be included in a list of preferred tubes for hi-fi amplification.
In my experience most tubes of any given type
number have similar characteristics - irrespective of manufacturer - however it
is worth mentioning that some current production tubes have different
specifications, characteristics and ratings to the original type number specs.
In other words, some current manufacturers have abandoned the convention of
building a tube that strictly conforms to internationally recognised,
"once-only" specifications for any specific type number, permanently
determined at the time of original registration.
The standard protocol has always been that an
incremental change or variant requires either a suffix or a new type number.
Proceed with caution.
OUTPUT TUBES
The choice of output stage configuration will
have already been made, and that will determine the first main category of tube
– i.e. triode, tetrode, pentode or beam power tube.
Top cap or plain.
The next step is to select a tube that will
deliver the required power output.
Tube handbooks usually provide typical
operating characteristics for a range of conditions so the choice must be made
to determine actual operating conditions.
Classes of operation, fixed or cathode bias and
type of interstage coupling from the driver stage need to be determined.
This set of decisions will determine:
· Grid #1 bias voltage
· Grid #1 resistor or transformer impedance
· Cathode bias resistor (if fitted) and bypass
capacitor spec's
· Output transformer load impedance
· Simple or complex transformer
.
.
Notwithstanding any other considerations, there is no doubt that
for a sweet natural sound, the TRIODE is best.
Next comes the ULTRA-LINEAR
option using BEAM POWER TUBES – after Triodes is best for bass.
TETRODE or PENTODE or BEAM
POWER TUBE operation is ideal for electric guitar and is the most commonly used
system throughout the music industry.
TUBE MOUNTING
Tubes may be mounted:
·
vertically with base down (the most common
configuration)
·
vertically with base up
(may require a restraining device to prevent the tube from falling out of its
socket)
·
horizontally
(best for multiple tube configurations because the heat is able to dissipate
more easily)
.
NOTE:
In the case of horizontal mounting, tubes should be mounted with the grid wires
aligned in the vertical plane - to prevent grid sag when hot and consequent
risk of changing grid characteristics - or even creating an inter-electrode
short-circuit. This mounting configuration also enhances heat dissipation into
the surrounding air, resulting in cooler operation.
The
harder the tubes are operated – i.e. more volts and more amps – the more likely
the grid wires will overheat.
WARNING: SOME TUBE TYPES ARE NOT
MANUFACTURED WITH CONSISTENT TUBE ELEMENT ORIENTATION IN RELATION TO THEIR BASE
PIN CONFIGURATION - THESE TUBES ARE NOT DESIRABLE FOR HORIZONTAL MOUNTING
CONFIGURATIONS BECAUSE REPLACEMENT TUBES MAY HAVE A DIFFERENT ORIENTATION THAN
THE ORIGINAL USED TO DETERMINE CHASSIS LAYOUT.
In all cases at least 6 mm or 1/4" inch
spacing must be provided between tubes to ensure their bulb temperature does
not exceed rated limits. Ensure the actual Plate Dissipation does not exceed
the rated value for the tube.
Adequate ventilation is
essential. Do not mount tubes near components likely to ignite or to be
affected by heat – e.g. electrolytic capacitors, transformers, cables, plastic
components, wooden cabinets etc. - allow at least 2 inches (50 mm) free air
clearance. Electrolytic capacitors can dry out then explode.
In the case of rectifiers and power tubes the
most common tube internal design configuration is where the Plate assembly is approximately
rectangular in section - often with a join in the centre of the wide faces.
The vertical wire posts that support the
Plate assembly are nearly always on the hottest faces of the tube - often
accompanied by extra cooling fins that extend out from the Plate.
In all cases it is advisable to instal the
tube such that the wide face of the Plate - which is the hottest part of the
tube - is facing away from adjoining components or other tubes.
The Cathode and Grid wires can sometimes be
seen from the outside and these indicate how the tube is constructed, however
in the case of Beam Power Tubes the internal wires are usually hidden inside
the Plate and Beam electrode assembly.
If a cooling fan (easy nowadays with the
availability of low-cost computer fans) is installed, ensure the fan blows
towards the narrow face of the Plate assembly so that heat radiated from both
sides of the Plate is cooled. Do not instal the fan too close to a rectifier or
power tube because the RADIATED heat will extend a significant distance - allow
at least 50 mm (2") clearance between a fan and a power tube.
PREAMP and DRIVER TUBES
Here we have a wide choice, but essentially
it is one of triodes or pentodes.
Both styles come in low, medium or high gain
varieties.
Triodes are available in single or twin
styles (in the same bottle)
Guitar and Bass amplifiers often operate
under severe conditions of vibration - just feel the floor of a stage!!!!.
Recommended tubes for low-noise, low hum and
low microphony, are the 12AY7/6072 triode and EF86/6BK8/Z729/M8195 pentode,
however very good results will be obtained from more readily available tubes.
In general the 6AV6/12AX7/7025 family provide
a "bright" sound, or tone, the 12AT7, or 12AU7 or 12AV7 a
"neutral" or "natural" sound, and the 6CG7/6SN7 a
"gutsy" or "bassy" sound. All of course, will provide a
"flat" frequency response when an amplifier is on test.
All popular tube types are available in
military or industrial versions – usually vintage stock.
The “W” suffix after the type number
generally means “ruggedised” for rough conditions – such as a guitar amp on
stage. Refer to the tube data sheet to confirm.
The letter “A” suffix after the type number
generally means a controlled heater warm-up time. This helps reduce switch-on
surge current to the rectifier tube. The letter “A” sometimes refers to a
different attribute so check the data sheet.
The letters “B” and “C” refer to upgrades
from the original type - check the data sheet.
The letter “G” refers to a glass bottle
upgrade from the original metal type - check the data sheet.
The letters GT, GTA, GTB, GA, GB and GC”
refer to upgrades from the original glass bottle type - check the data sheet.
Many tubes are made in variants from the
original version. Variants have a different type number and may have higher
ratings or a different pinout - check the data sheet.
Many tubes having USA, Euro, British, Russian,
Chinese, Japanese, Indian and other type numbers are interchangeable - check
the data sheets.
Euro type numbers sometimes have “SQ - special
quality” equivalents offering a 10,000 hour life and other attributes. The type
numbering of popular types is re-arranged to indicate the SQ version. e.g. an
EL84 becomes an E84L (SQ version) or EF86 becomes an E86F. Check the data
sheets.
US SQ tubes have a 4 digit number – refer data
sheets.
US military and industrial tubes have a 4
digit number – refer data sheets.
It is wise to consult the tube specs to
determine why it has an industrial number, because often the industrial
characteristic have no impact on "sound" at all – e.g. long life. It
may be "ruggedised" or have particular selection, inspection or test
characteristics directed at specific non-audio applications.
Note however, regardless of type number, it
is well established empirically, that the material and dimensions of the Plate
element affect the sound tonal characteristics and many audiophiles have
specific preferences in this regard.
My personal preference is for long black
plates in all tubes. Plate material varies from manufacturer to manufacturer
and between batches and is not shown in tube data sheets.
The choice of an "industrial" grade
or "premium quality" tube does not always provide superior results to
a domestic equivalent.
Where possible, choose Preamp and
Phase-splitter tubes that have a high heater/cathode voltage rating – usually
200 VDC.
Prefer Preamp and Phase-splitter tubes that
have twisted heater wires. This hum-reducing feature is not mentioned in data
sheets so look inside the tube bottle.
Some of the RCA Hi-Fi circuits use pentodes,
such as the 6AU6, 6CB6, 6U8, and 5879. There is also the Euro EF86.
Irrespective of the class of tube – i.e.
receiving, industrial, RF, military or hi-fi - care should be taken in
selecting actual tubes - for any given type number there are very wide
variations in tube characteristics such as hum, noise, microphony and
reliability. The most reliable method is to just plug a tube in and try it.
Where substitute or equivalent type numbers
are selected, check the tube specs to ensure the pinout matches the socket
wiring.
Note: Some modern
production twin triodes are fitted with smaller diameter pins than vintage
tubes. Consequently modern sockets may not accept vintage tubes.
Sometimes it will be necessary to use
shielding cans around driver tubes to eliminate hum and stray RF pickup - however
cans tend to increase the risk of microphony (mechanical feedback).
Do not mount driver stage tubes near magnetic
components such as transformers or loudspeakers - to prevent magnetic
interaction or hum induction. This is
relevant to combo amps where the chassis is inverted and tubes are located
close to the speaker magnet and cone vibrations.
Microphony can be an issue in combo amps. If
present it may be necessary to change the tubes until a quiet unit is found, or
try a “W” version if available. The 6SL7 is renown for microphony but can be
replaced by the military 5691.
SPARE TUBES
Always carry a spare set of
tubes – and fuses.
Although quality manufactured
tubes can last 20 to 30 years or more, some commercial guitar amplifier designs
push the tubes to their limits so last no more than a year or two.
Worn power tubes produce less
power.
Worn preamp tubes generally
lose top end and sound dull.
The reason electron tubes
are plug-in is because they can wear out over time or fail.
A failed tube can be easily
replaced in-situ, whereas failed solid state devices usually require a trip to
the service shop and big bucks in parts and labour.
All tubes are designed to
run hot so DO NOT try to replace a hot tube with bare hands.
When installing or removing a
tube always CAREFULLY insert or remove it perpendicular to the socket face to
avoid bending the pins.
Miniature 7 and 9 pin tube
pins must be carefully oriented with the socket to ensure the tube is not
inserted incorrectly into the wrong socket terminals.
If a tube fails during a gig
it can be replaced in a few minutes – depends mainly on access to the socket.
If you are designing and
building your own amplifier make sure the covers can be removed easily and quickly.
Holding up a show while you repair your amp is not well received by your
audience.
Always carry the right tools
to enable replacement – might be just a screwdriver.
NEW OR USED – WHICH IS BETTER?
Many people believe the only
good tube is a new one.
But a moment’s thought tells
us that the only difference between a new and used tube is that as soon as a
new tube is plugged in and switched on it becomes used.
Tubes are vacuum sealed, can
sit on a shelf for 60 years then work first time plugged in.
What does matter is the
condition of the tube and its performance.
Tube tests tell us that many
new tubes have low emission as a result of manufacturing tolerances. So a low
new tube can be not as good as a high used tube.
What is more important is
that tubes in a full-wave rectifier, push-pull phase inverter stage, or power
output stage are matched for current. Where the amplifier provides adjustable
grid bias matching is not so important.
So long as a tube does the
job for which it intended it can be regard as good.
CARE
DO NOT wash electron tubes with water or detergent because
the type number will be washed off.
Some tube types can be recognised by their construction but
most of the twin triode family look the same
Try not to drop a tube onto a concrete floor. Miniature tubes
tend to survive but expensive power tubes will most likely shatter.
To ensure good contact in the tube socket clean the tube pins
with a toothbrush to remove dirt and grime. Chemical cleaners can be used but
keep away from the bottle lettering.
REMEMBER - ALWAYS TAKE CARE WHEN WORKING WITH
HIGH-VOLTAGE - DEATH IS PERMANENT!!
Contact:
"electron"
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This page last modified 11 July 2023