Showing posts with label Neon. Show all posts
Showing posts with label Neon. Show all posts
Thursday, September 25, 2014
Simple Neon Lamp Tester Circuit
- This tester can also be used to check IF transformers used in AC mains operated radio receiver.
- Though this tester is not very accurate, it can give a reasonably good indication about the condition of the components being tested.
- Neon lamps are ideal indicators for simple testers to check large resistances of leaky capacitors and mains lF transformers.
- For accuracy, the component being tested should not have any shunting resistance. lf a shunting resistance is present, disconnect one end of it before testing.
- Such a defective component cannot be easily tested with simple test equipment.
- The tester circuit uses a relaxation oscillator, the frequency of which is determined by capacitor Cl and the external resistance (leakage resistance of the component under test) between the probes.
- Two flashes per second on neon lamp indicates 200 megohm leakage resistance, four flashes l00 megohm, eight flashes 50 megohm, and so on.
- Moreover, as it tests capacitors at a fairly high voltage—closer to that of the operating voltage-it offers an advantage over a VTVM which is operated at a low voltage and gives inconclusive results.
- Being high-voltage, low-current devices, the neon lamps are very sensitive.
- The grid of an IF amplifier usually has a high AC impedance and its primary is operated at a high voltage.
- A small leak in the lFl` can cause considerable trouble.
Wednesday, September 24, 2014
Simple Neon Tube Flasher Circuit
Flashing neon globes have use in many applications, however their relatively high working voltage precludes their general use where a mains supply is not available.
This simple neon tube flasher circuit enables neon tubes or bulbs to be operated from a low voltage dc supply. The voltage required to ignite the neon tube is obtained by using an ordinary filament transformer (240-6.3Vl in reverse. Battery drain is quite low being in the region of 1 to 2 milliamps for a nine volt battery. O1 is a unijunction transistor and operates as a relaxation oscillator. its frequency of operation is determined by R2-C1. The pulses from Q1 are directed to O2 which in tum drives O3 into saturation. The sharp rise in current through the 6.3V winding of the transformer as 03 goes into saturation induces a high voltage in the secondary winding causing the neon to flash. The diode D1 protects the transistor from high voltage spikes generated when switching currents in the transformer.
This simple neon tube flasher circuit enables neon tubes or bulbs to be operated from a low voltage dc supply. The voltage required to ignite the neon tube is obtained by using an ordinary filament transformer (240-6.3Vl in reverse. Battery drain is quite low being in the region of 1 to 2 milliamps for a nine volt battery. O1 is a unijunction transistor and operates as a relaxation oscillator. its frequency of operation is determined by R2-C1. The pulses from Q1 are directed to O2 which in tum drives O3 into saturation. The sharp rise in current through the 6.3V winding of the transformer as 03 goes into saturation induces a high voltage in the secondary winding causing the neon to flash. The diode D1 protects the transistor from high voltage spikes generated when switching currents in the transformer.
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