Assembly Instructions
for the
3.1 MHz Switch Mode Plasma
Tube Driver Amplifier Kit
PA2 Amplifier shown mounted on HS2 Heat Sink
(The HS2 is not included in kit K1)
Manual v1.00
© 2013 by Ralph Hartwell
Spectrotek Services
All Rights Reserved
The PA2 is a high-frequency switch mode power supply module designed
to furnish a square wave modulated high voltage alternating current at a
frequency of approximately 3.1 MHz across a 50 ohm load impedance.
If the PA2 is installed incorrectly or used improperly, it is capable of
causing severe radio frequency interference. To prevent this from
occurring, observed the following warnings:
The PA2 is to be used as a research device only, or as part of a complete
system to drive a plasma tube.
The PA2 is not intended to be used for any form of radio transmission in
any manner whatsoever.
The PA2 is not intended to be connected to an antenna or to any radiating
element or to be used for any form of radio communications purposes in
any manner whatsoever.
The PA2 is designed solely to be a source of power to light a plasma tube.
All electrical connections to the output terminals of the PA2 are to be
made by the use of properly shielded 50-ohm coaxial cable capable of
handling at least 500 watts at 3.1 MHz.
All connections are to be made in such a manner as to minimize any RF
radiation from the connecting wires to the PA2.
The PA2 has been specifically designed to be driven by a low-level signal
such as is generated by the SSQ-2F v1.41, a GB-4000, or an Atelier
Robin F165, F170 or F175 frequency generator. The PA2 will accept
either a sine or square wave driving signal. However, the PA2 is not a
linear amplifier, and it will not function as such.
The operating frequency range of the PA2 has been restricted to a 1 MHz
portion of the spectrum centered at 3.1 MHz.
Any attempt to drive the PA2 with a radio frequency source such as a CB
radio transmitter, will result in either no power output from the PA2 or
immediate destruction of the STW20NK50Z MOSFET in the PA2.
Arrange for a clean work surface with adequate lighting. You will be working with small
parts, and you may need to use a magnifier for close work. Working on a soft surface,
such as a short nap towel, prevents parts from rolling off the work area and falling on the
You will be soldering small parts in place. If you are not used to soldering such items, it
is suggested that you seek assistance from an experienced person before starting
The circuit board of the PA2 has been designed with ruggedness in mind. Extra-wide and
thick copper traces have been used on the PA2. Because of this, the PA2 will withstand
repeated soldering should repairs be necessary, such as if a part has been installed in an
incorrect location. Nevertheless, it is strongly recommended that you take care in locating
the position of the various parts when assembling your PA2.
You will require the following tools:
Small needle-nose pliers to install the heat sink.
Small flush-cut or side-cutter pliers to cut off the excess wire ends of parts after
soldering them in place.
A #1 Phillips head screwdriver to install the heat sink.
A soldering iron, with a recommended wattage of between 30-70 watts, and a tip
temperature of no more than 700º F. The tip should be a small conical point.
Solder, 60/40, 63/37, or 62/36/2 grade, no larger in diameter than 0.032”. rosin
core flux only. Suitable types are Radio Shack 64-013 and 64-009.
If you prefer, you may use a lead-free solder instead. The PA2 circuit board is
compatible with all lead-free solders.
WARNING! DO NOT use acid core solder!!
Doing so will cause damage to the circuit board and will void any and all
warranties. We will NOT warranty any circuit boards that have been assembled
using any type of acid core solder.
WARNING! The STW20NK50Z is Static Sensitive!!
The STW20NK50Z MOSFET transistor in your PA2 kit has been tested before
shipment. Your STW20NK50Z has been wrapped in aluminum foil to prevent
damage from static electricity during shipment.
Please do not unwrap the STW20NK50Z until you are ready to install it. Be sure to
use antistatic precautions while installing the STW20NK50Z in your PA2 circuit
The wire leads of almost all of the parts will need to be carefully bent (usually at right
angles to the body of the part) according to the assembly instructions. Bend the part leads
using ONLY your fingers! Unless used very carefully, using pliers to bend the leads may
cause the body of the part to break or crack where the lead attaches to the body of the
part. This can result in outright failure of the PA2 to operate, or even worse, it may cause
intermittent malfunctions during operation. Such problems can be very difficult to
Although you may assemble the various parts of the PA2 kit in almost any order, the
following sequence allows you to “build up” from the surface of the board, making it
easier to install the remainder of the parts as you assemble your PA2.
It is suggested that you take the time to inspect the blank circuit board and
familiarize yourself with where the various parts will be installed. Please refer to the
photograph of the complete PA2 in the back of this manual for help in locating the
position of the parts.
If you look at the blank circuit board, you will see that one side of the blank circuit board
has a serial number engraved on it. This is the Solder Side of the circuit board. The other
side of the board, the Parts Side, has the part number “STW20NK50Z” placed next to the
three mounting holes for the STW20NK50Z transistor. All of the parts are to be installed
on the side of the board that has the STW20NK50Z identification. All of the soldering is
done on the opposite (Solder Side) of the board.
The parts side of the board also has outline drawings of all the parts, as well as their part
number, (C1, R1,) or their value, (1500, 0.47,) thus making it easy to identify where the
various parts should be placed.
For each assembly step, locate the listed part, and identify where on the circuit board it
will be placed. Some of the parts in this kit may be furnished with the leads already prebent to the correct shape for insertion in the PA2 circuit board. However, some kits may
include parts with leads that have not been pre-bent. If you have one of these kits, it will
be necessary to carefully bend the leads of some of the parts to fit. When this is
necessary, it will be in the assembly instructions.
After inserting the leads of each part through the proper holes in the PA2 circuit board,
carefully tug on the free end of the wire lead to seat the part close to the circuit board. Do
not apply excessive force trying to seat the part firmly against the board. If the part is
positioned slightly above the board, that is OK.
Note that several parts must be installed so that they are sitting slightly above the surface
of the circuit board, and not tightly in contact with it. This is done for proper heat
dissipation when the PA2 is in operation. If these parts are not properly spaced above the
board, it is possible for the PA2 to fail during operation.
After inserting each part, bend the free ends of the wire leads at a 45º angle to prevent the
part from slipping out of the circuit board when the board is turned upside down to solder
the part in place.
Solder the part in place, inspect the solder joint, and then cut off the excess lead wires
with the flush cutter pliers.
As you install each part, put an “X” or a check mark in the “” box to the left of each
part. Assembling the parts in sequence helps to prevent assembly errors.
Install ( 2 ) 1N4148 Diodes
Please be sure to orient the black cathode band on the 1N4148 diodes to match the
markings on the circuit board.
Install ( 1 ) 5 Volt Zener Diode
Please be sure to orient the black cathode band on the Zener diode to match the marking
on the circuit board.
Install ( 1 ) 4700 Ohm Resistor
4700 Ohm ( Yellow Violet Red )
Install ( 1 ) 470 Ohm Resistor
470 Ohm ( Yellow, Violet, Brown )
Install ( 1 ) 18 K Ohm Resistor
18,000 Ohm ( Brown, Gray, Orange )
Install ( 1 ) 8-Pin DIP Socket
Install ( 1 ) 4-Pin White plastic connector for cooling fan
When installing the terminal blocks, be sure to install them so that the holes for the
connecting wires are facing away from the circuit board.
Depending on manufacturing tolerances, the terminal blocks may be a tight press fit into
the circuit board. Be sure to seat the terminal block completely against the circuit board
before soldering. Double check to make sure the wire holes in the terminal blocks are
facing the outer edge of the circuit board before soldering the terminal blocks in place.
To make soldering the terminal boards onto the circuit board an easier task, insert the
terminal blocks onto the circuit board and hold them in position with your hand. Now,
turn the board upside down and carefully place it down on the surface of your
workbench. The PA2 circuit board should now be laying flat against the back of each of
the terminal blocks. It is now an easy task to solder the terminal blocks into position.
Install ( 1 ) 2 Position Terminal Strip at This Location:
Install ( 1 ) 6 Position Terminal Strip at This Location:
GND - +19, GND - + HV, PWR, GND - RF OUT
Install ( 1 ) 3 Position Terminal Strip at This Location:
Install ( 2 ) 47 uF 16 V Electrolytic capacitors
Install ( 1 ) 1000 pF Disc Capacitors
1 nF
Install ( 2 ) 2200 pF Disc Capacitors
Install ( 1 ) 8200 pF Poly Film Capacitor
Install ( 1 ) 15 Ohm 1 Watt Resistor
Bend one of the leads of the resistor down towards the body of the resistor so that both
leads point in the same direction.
Install ( 3 ) 4.7 uH Ferrite Core Inductors
Please see the photographs at the back of this assembly manual for correct orientation of
these inductors before soldering them in place.
Bend one of the leads of each inductor down towards the body of the inductors so that
both leads point in the same direction.
Mount the inductors vertically with the inductor bodies placed against the PA2 circuit
board against the solder holes that do not have traces visible on the Parts Side of the
circuit board. The folded over wire lead should pass through the hole in the circuit board
which has a copper trace connecting to the solder pad.
Install ( 2 ) 7.5 Ohm Resistors
Please see the photographs at the back of this assembly manual for correct orientation of
the resistors before soldering them in place.
Bend one of the leads of the resistor down towards the body of the resistor so that both
leads point in the same direction.
Mount the resistors vertically with the resistor bodies centered over the outermost holes
in the mounting pads. There is a diagonal trace connecting the two solder holes where the
unbent lead of each of the resistors will be soldered. The bottom end of each resistor
should be standing about 1/4 inch or 6 mm above the surface of the circuit board.
Mounting the resistors in this manner allows the maximum cooling airflow between the
7.5 Ohm ( Violet Green Gold Gold )
7.5 Ohm ( Violet Green Gold Gold )
Install ( 5 ) 0.47 uF capacitors
Install ( 1 ) 2200 pF Mica Capacitor (Rectangular)
The capacitor should be mounted “on edge.”
Looking at the PA2 circuit board, you will notice that there is a double part outline and
four mounting holes on the circuit board provided for the installation of the 2200 pF Mica
capacitor. Depending on the style of Mica capacitor supplied in your kit, you will use
either the outer two holes or the inner two holes to mount the Mica capacitor.
Please see the photographs at the back of this assembly manual for correct orientation of
the capacitor.
Install ( 1 ) 470 uF 25 V Electrolytic Capacitor
Install ( 1 ) 220 uF 200 V Electrolytic Capacitor
Install ( 1 ) MC7812 Voltage Regulator
NOTE – Be sure to install the MC7812 so that the exposed metal side of the device is
facing away from the circuit board.
Install ( 1 ) IRF730P MOSFET Transistor
NOTE – Be sure to install the IRF730P so that the exposed metal side of the device is
facing away from the circuit board.
Install ( 1 ) L3 Air Core Inductor
Please see the photographs at the back of this assembly manual for correct orientation of
this inductor before soldering it in place.
The air core inductor L3 in your PA2 kit is supplied with leads that are cut to the proper
length. Make sure that the enamel insulation is removed from the outermost ¼” of each
connecting wire on L3.
If necessary, carefully bend the wires on L3 so that they pass through the mounting holes
in the PA2 circuit board. Be careful not to bend the leads too far so as not to split the
plastic insulation that holds the coil turns together. Insert the leads of L3 through the
holes in the circuit board and carefully solder them in place.
Install ( 2 ) TO220 Mini Heat Sinks
NOTE: It is advisable to apply a small amount of heat sink compound (“thermal grease”)
to the heat sink before attaching the heat sink to the transistor or voltage regulator.
Install on MC7812 Voltage Regulator
Install on IRF730P MOSFET Transistor
Install ( 1 ) TC4427 Integrated Circuit in its socket.
4427 socket (Previously installed.)
Install ( 1 ) STW20NK50Z Transistor
Using the 3-connector terminal block for mounting the STW20NK50Z, simply insert the
pins of the STW20NK50Z as far as they will go into the holes of the terminal block and
gently but firmly tighten the clamping screws of the terminal block.
Note that when you mount the PA2 circuit board in its final location, it may be necessary
to bend the pins of the STW20NK50Z in order to obtain the proper clearance of the PA2
circuit board from the heat sink.
When installing the transistor on the heat sink, be sure to use the supplied Bergquist
thermal pad (white in color) or a good quality, high thermal transfer insulating sheet
between the transistor and the heat sink.
The heat sink used should be able to dissipate a heat load of 100 watts or more.
The part of the heat sink where the MOSFET is mounted must be at least 3/8 inch / 9.25
mm thick. This is necessary so that it will be able to spread out the heat from the
MOSFET. Using a heat sink with less thickness risks damage to the MOSFET due to
overheating at high power levels,
Using a magnifying glass and a bright light, carefully inspect the top and bottom of the
finished circuit board for any unwanted solder splashes between connections, short wire
clippings, or anything else that may cause problems during operation of the PA2.
Should you wish to remove the solder flux residue from the finished circuit board, you
may use a commercial flux remover or 100% Isopropyl alcohol. Use only 100%
Isopropyl alcohol. Rubbing alcohol is NOT suitable for removing the flux residue due to
its high water content and the denaturing ingredients contained in rubbing alcohol. After
cleaning the board, allow it to dry thoroughly before continuing.
This completes the assembly of the PA2 circuit board.
The following resistance checks are to be taken with no external connections to the
circuit board.
Using an Ohmmeter, measure the resistance between the + 19 and GND terminals and
between the + HV and GND terminals. The resistance readings should be greater than
one Megohm. The resistance reading may be low at first when the Ohmmeter leads are
connected, but the resistance reading will increase as the filter capacitors charge up from
the Ohmmeter voltage,.
After the resistance reading stabilizes, reverse the Ohmmeter leads and make sure the
resistance in the reverse direction also reads greater than one Megohm.
Your PA2 module is now ready for use. Please consult the
PA2 Instruction Manual for final setup and operating
Partially Assembled PA2 - Showing Correct Orientation of Parts.
Inductor L3, TO220 Heat Sinks, TC4427 and STW20NK50Z are not yet installed.
Assembled PA2
Inductor L3, TO220 Heat Sinks, TC4427 and STW20NK50Z have been installed.
Schematic Diagram of the PA2
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