Wiring Circuit

• The bulb must be a low current type (12V 40-50mA or 6V 50mA) in order to obtain good long term stability and low distortion.
• Distortion @ 1V RMS output is 0.15% using a 12V 40mA bulb, raising to 0.5% with a 12V 100mA one.
• Using a bulb differing from specifications may require a change of R6 value to 220 or 150 Ohms to ensure proper circuits oscillation.
• Set R5 to read 1V RMS on an Audio Millivoltmeter connected to the output with R7 rotated fully clockwise, or to view a sinewave of 2.828V Peak-to-Peak amplitude on the oscilloscope.
• With C1, C2 = 100nF the frequency generated is 100Hz and with C1, C2 = 1nF frequency is 10KHz but R5 requires adjustment.
• High gain transistors are preferred for better performance.

Parts:

R1____________5K6  1/4W Resistor

R2____________1K8  1/4W Resistor

R3,R4________15K   1/4W Resistors

R5__________500R   1/2W Trimmer Cermet

R6__________330R   1/4W Resistor

R7__________470R   Linear Potentiometer

C1,C2________10nF  63V Polyester Capacitors

C3__________100µF  25V Electrolytic Capacitor

C4__________470nF  63V Polyester Capacitor

Q1,Q2_______BC238  25V 100mA NPN Transistors

LP1___________12V  40mA Filament Lamp Bulb (See Notes)

J1__________Phono chassis Socket

SW1__________SPST  Slider Switch

B1_____________9V  PP3

Clip for 9V PP3 Battery