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3 watt fm transmitter

This is a circuit that I’ve build a few years ago for a friend, who used it in combination with the BLY88 amplifier to obtain 20 W output power. From the notes that I made at the original schematic, it worked fine with a SWR of 1 : 1.05 (quite normal at my place with my antenna).


This is the schematic of the 3W FM Transmitter


Part Total Qty. Description Substitutions
R1,R4,R14,R15 4 10K 1/4W Resistor
R2,R3 2 22K 1/4W Resistor
R5,R13 2 3.9K 1/4W Resistor
R6,R11 2 680 Ohm 1/4W Resistor
R7 1 150 Ohm 1/4W Resistor
R8,R12 2 100 Ohm 1/4W Resistor
R9 1 68 Ohm 1/4W Resistor
R10 1 6.8K 1/4W Resistor
C1 1 4.7pF Ceramic Disc Capacitor
C2,C3,C4,C5,C7,C11,C12 7 100nF Ceramic Disc Capacitor
C6,C9,C10 3 10nF Ceramic Disc Capacitor
C8,C14 2 60pF Trimmer Capacitor
C13 1 82pF Ceramic Disc Capacitor
C15 1 27pF Ceramic Disc Capacitor
C16 1 22pF Ceramic Disc Capacitor
C17 1 10uF 25V Electrolytic Capacitor
C18 1 33pF Ceramic Disc Capacitor
C19 1 18pF Ceramic Disc Capacitor
C20 1 12pF Ceramic Disc Capacitor
C21,C22,C23,C24 4 40pF Trimmer Capacitor
C25 1 5pF Ceramic Disc Capacitor
L1 1 5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L2,L3,L5,L7,L9 5 6-hole Ferroxcube Wide band HF Choke (5 WDG)
L4,L6,L8 3 1.5 WDG, Dia 6 mm, 1 mm CuAg, Space 1 mm
L10 1 8 WDG, Dia 5 mm, 1 mm CuAg, Space 1 mm
D1 1 BB405 BB102 or equal (most varicaps with C = 2-20 pF [approx.] will do)
Q1 1 2N3866
Q2,Q4 2 2N2219A
Q3 1 BF115
Q5 1 2N3553
U1 1 7810 Regulator
MIC 1 Electret Microphone
MISC 1 PC Board, Wire For Antenna, Heatsinks


  1. Email Rae XL Tkacik with questions, comments, etc.
  2. The circuit has been tested on a normal RF-testing breadboard (with one side copper). Make some connections between the two sides. Build the transmitter in a RF-proof casing, use good connectors and cable, make a shielding between the different stages, and be aware of all the other RF rules of building.
  3. Q1 and Q5 should be cooled with a heat sink. The case-pin of Q4 should be grounded.
  4. C24 is for the frequency adjustment. The other trimmers must be adjusted to maximum output power with minimum SWR and input current.
  5. Local laws in some states, provinces or countries may prohibit the operation of this transmitter. Check with the local authorities.

22 watt audio amplifier

The 22 watt amp is easy to build, and very inexpensive. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts. The circuit is not mine, it came from Popular Electronics.


This is the schematic of the 22 Watt Amp


Part Total Qty. Description Substitutions
R1 1 39K 1/4 Watt Resistor
C1,C2 2 10uf 25V Electrolytic Capacitor
C3 1 100uf 25V Electrolytic Capacitor
C4 1 47uf 25V Electrolytic Capacitor
C5 1 0.1uf 25V Ceramic Capacitor
C6 1 2200uf 25V Electrolytic Capacitor
U1 1 TDA1554 Two Channel Audio Amp Chip
MISC 1 Heatsink For U1, Binding Posts (For Output), RCA Jacks (For Input), Wire, Board


  1. The circuit works best with 4 ohm speakers, but 8 ohm units will do.
  2. The circuit dissipates roughly 28 watts of heat, so a good heatsink is necessary. The chip should run cool enough to touch with the proper heatsink installed.
  3. The circuit operates at 12 Volts at about 5 Amps at full volume. Lower volumes use less current, and therefore produce less heat.
  4. Printed circuit board is preferred, but universal solder or perf board will do. Keep lead length short.

12v to 24v dc-dc converter circuit

This simple DC-DC converter can provide up to 24V from a 12V source. It can be used to run radios, small lights, relays, horns and other 24V accessories from a 12V vehicle with a maximum draw of about 800mA. It can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won’t drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses.


Schematic for the 12 To 24V DC-DC Converter circuit


Part Total Qty. Description Substitutions
R1, R2, R3, R4, R8, R7 6 100K 1/4W Resistor
R5 1 470 Ohm 1/2W Resistor
R6 1 10K Linear Pot
C1 1 0.01uF Mylar Capacitor
C2 1 0.1uF Ceramic Disc Capacitor
C3 1 470uF 63V Electrolytic Capacitor
D1 1 1N4004 Rectifier Diode
D2 1 BY229-400 Fast Recovery Diode See Notes
Q1 1 BC337 NPN Power Transistor
U1 1 LM358 Dual Op Amp IC
L1 1 See Notes
MISC 1 Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1


  1. R6 sets the output voltage. This can be calculated by Vout = 12 x (R8/(R8+R7)) x (R6B/R6A).
  2. L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H).
  3. D2 can be any fast recovery diode rated at greater then 100V at 5A. It is very important that the diode be fast recovery and not a standard rectifier.
  4. Q1 will need a heatsink.

12v to 120v inverter

Have you ever wanted to run a TV, stereo or other appliance while on the road or camping? Well, this inverter should solve that problem. It takes 12 VDC and steps it up to 120 VAC. The wattage depends on which tansistors you use for Q1 and Q2, as well as how “big” a transformer you use for T1. The inverter can be constructed to supply anywhere from 1 to 1000 (1 KW) watts.

Important: If you have any questions or problems with the circuit, see the forum topic linked to in the Notes section. It will answer all your questions and provide links to many other (and better) inverter circuits.


This is a schematic of the Inverter


Part Total Qty. Description Substitutions
C1, C2 2 68 uf, 25 V Tantalum Capacitor
R1, R2 2 10 Ohm, 5 Watt Resistor
R3, R4 2 180 Ohm, 1 Watt Resistor
D1, D2 2 HEP 154 Silicon Diode
Q1, Q2 2 2N3055 NPN Transistor (see “Notes”)
T1 1 24V, Center Tapped Transformer (see “Notes”)
MISC 1 Wire, Case, Receptical (For Output)


  1. Q1 and Q2, as well as T1, determine how much wattage the inverter can supply. With Q1,Q2=2N3055 and T1= 15 A, the inverter can supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power.
  2. The easiest and least expensive way to get a large T1 is to re-wind an old microwave transformer. These transformers are rated at about 1KW and are perfect. Go to a local TV repair shop and dig through the dumpster until you get the largest microwave you can find. The bigger the microwave the bigger transformer. Remove the transformer, being careful not to touch the large high voltage capacitor that might still be charged. If you want, you can test the transformer, but they are usually still good. Now, remove the old 2000 V secondary, being careful not to damage the primary. Leave the primary in tact. Now, wind on 12 turns of wire, twist a loop (center tap), and wind on 12 more turns. The guage of the wire will depend on how much current you plan to have the transformer supply. Enamel covered magnet wire works great for this. Now secure the windings with tape. Thats all there is to it. Remember to use high current transistors for Q1 and Q2. The 2N3055’s in the parts list can only handle 15 amps each.
  3. Remember, when operating at high wattages, this circuit draws huge amounts of current. Don’t let your battery go dead :-).
  4. Since this project produces 120 VAC, you must include a fuse and build the project in a case.
  5. You must use tantalum capacitors for C1 and C2. Regular electrolytics will overheat and explode. And yes, 68uF is the correct value. There are no substitutions.
  6. This circuit can be tricky to get going. Differences in transformers, transistors, parts substitutions or anything else not on this page may cause it to not function.
  7. If you want to make 220/240 VAC instead of 120 VAC, you need a transformer with a 220/240 primary (used as the secondary in this circuit as the transformer is backwards) instead of the 120V unit specified here. The rest of the circuit stays the same. But it takes twice the current at 12V to produce 240V as it does 120V.
  8. Check out this forum topic to answer many of the most commonly asked questions about this circuit: 12 – 120V Inverter Again. It covers the most common problems encountered and has some helpful suggestions.

6v to 12v converter

This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.


This is the schematic of the Voltage Inverter


Part Total Qty. Description Substitutions
R1, R4 2 2.2K 1/4W Resistor
R2, R3 2 4.7K 1/4W Resistor
R5 1 1K 1/4W Resistor
R6 1 1.5K 1/4W Resistor
R7 1 33K 1/4W Resistor
R8 1 10K 1/4W Resistor
C1,C2 2 0.1uF Ceramic Disc Capacitor
C3 1 470uF 25V Electrolytic Capcitor
D1 1 1N914 Diode
D2 1 1N4004 Diode
D3 1 12V 400mW Zener Diode
Q1, Q2, Q4 3 BC547 NPN Transistor
Q3 1 BD679 NPN Transistor
L1 1 See Notes
MISC 1 Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board


  1. L1 is a custom inductor wound with about 80 turns of 0.5mm magnet wire around a toroidal core with a 40mm outside diameter.
  2. Different values of D3 can be used to get different output voltages from about 0.6V to around 30V. Note that at higher voltages the circuit might not perform as well and may not produce as much current. You may also need to use a larger C3 for higher voltages and/or higher currents.
  3. You can use a larger value for C3 to provide better filtering.
  4. The circuit will require about 2A from the 6V supply to provide the full 800mA at 12V.

power supply

When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find.


This is a schematic of the Power Supply


Part Total Qty. Description Substitutions
C1 1 14000uF or 10000uf 40 VDC Electrolytic Capacitor
C2 1 100uF 50Vdc Electrolytic Capacitor
C3 1 0.1uF Disc Capacitor
C4 1 0.01uF Disc Capacitor
R1 1 5K Pot
R2 1 240 Ohm 1/4 W Resistor See Notes
U1 1 LM338K 1.2 to 30 Volt 5 Amp Regulator
BR1 1 10 Amp 50 PIV Bridge Rectifier
T1 1 24 V 5 Amp Transformer
S1 1 SPST Toggle Switch
MISC 1 Wire, Line Cord, Case, Binding Posts (for output)


  1. The regulator comes in a TO-3 case and MUST be used with a LARGE heatsink. You may want to mount a small fan to blow air across the regulator (I did).
  2. The filter capacitor is large. It won’t fit on any board so bolt it to the case.
  3. You can, of course, add a volt and amp meter.
  4. Since this project operates from 120 VAC, you must include a fuse and build the project in a case.
  5. R2 may need to be decreased to 120 Ohm if you experience voltage drift at light loads. 240 Ohm may not load the output appropriately on some regulators. The datasheet for the LM338K does specify 120 Ohm (I suggest you use a 1/2W unit) so you may just want to use 120 Ohm and not bother with the 240 Ohm resistor showin the parts list. This has been discussed on the forum.




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