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  1. duke37

    Emitter Base Breakdown

    Thank for the replies and the experiment. Reverse current through the emitter/base junction will not necessarily create damage. I have a Heathkit HW100 transceiver which uses a transistor junction as a Zener diode. Duke
  2. duke37

    Resonance

    An efficient antenna must be at least a quarter wavelength long. The wavelength = 300 000 000/freq meters Work out the antenna size for 0.57Hz 500mhz is very low. Do you mean 500MHz?
  3. duke37

    Toroidal transfomer help

    There must be more than four wires. Two for the primary and three or four for the secondarys. The primary wires will be opposite to the secondaries and thinner wire. Give us the label again and a photo also.
  4. duke37

    Resonance

    An audio amplifier will only respond to RF signals if it is not working properly. It is anybody's guess how any particular amplifier does this. Some audio signal generators use a Wien bridge oscillator which can be tuned with a pair of ganged resistors or capacitors. A frequency range of...
  5. duke37

    Emitter Base Breakdown

    What happens to the collector current of an npn transistor when the permitted base emitter reverse voltage is exeeded. Using LTspice for a BC547B does not allow for junction leakage. The base voltage goes to -100V with no limit.
  6. duke37

    Simple Phototransistor switch circuit

    Yes, a 555 would do the job with a feedback resistor. It would replace the fet also if he only wants to drive a couple of leds.
  7. duke37

    TCI Ignition ( by bux15)

    The IGBT looks as if it will do what you want. I do not have a schematic for this. I made a capacitor discharge ignition 20 or 30 years ago and bought one by Sparkrite. These worked well. As I said before, a 1 ohm coil will dissipate a lot of heat and could well burn out if the points are...
  8. duke37

    Simple Phototransistor switch circuit

    The Op does not want a linear circuit, he wants to switch the output fully on or off. The positive feedback alters the set point to give a dead band. Perhaps *steve* or Harald could adjudicate on this.
  9. duke37

    Transistor ID help find

    Depending on what your meter does, it may be a germanium transistor with about 0.25 drop across the junctions. The base is the middle pin. You can find which is the emitter and collector by measuring the gain either way round. The measurements you have made would indicate that it is OK. What...
  10. duke37

    What value of capacitor to drop the ripple %

    You could connect the output with to a load of say a 12V headlight bulb and look at the number of pulses with an oscilloscope. It appears to be more than a rectifier, with SCRs there must be a control circuit. Information is creeping out bit by bit.
  11. duke37

    What value of capacitor to drop the ripple %

    In #4 we got some critical information. The supply is three phase and with full wave rectification there will be six pulses per cycle. The voltage will never drop to zero like a single phase supply, even so, I do not see a capacitor doing anything significant. It may be that a rectifier is...
  12. duke37

    Toroidal transfomer help

    A picture may help. Many amplifires have transformers that can be driven from either 230V or 125V AC by using a tap on the input winding or two windings which can be connected in series (230V) or parallel (125V) for use in different countries. There seems to be two indepedent output...
  13. duke37

    TCI Ignition ( by bux15)

    What is TCI? There are many circuits for transistorised ignition triggered by the points. To comment on your circuit. 1. The relay will give a time delay which could be unacceptable particularly at high revs. 2. The relay should not be necessary, the points originally took the full...
  14. duke37

    Simple Phototransistor switch circuit

    The two set points should be the npn fully on of fully off. The amount of hysteresis sould be set by a resistor in the collector. Too much feedback (too low a resistance) will latch the circuit in one direction permanently.
  15. duke37

    Bug zapper Q

    I misquoted, Wikipedia 'dielectric field strength of air' = 3MV/m or 3kV/mm If you are connecting to the mains you could be in danger.
  16. duke37

    1n400X complete datasheet

    The 1N4007 is 1000V, why go for less? The 1N4007 series is common and may be made by many manufactures so they may have different specifications. They do not seem to specify speed. The UF4007 is a high speed 1000V diode with specified switching time of 75ns.
  17. duke37

    Simple Phototransistor switch circuit

    EinarA That looks like a good start, however, I would drive the base from the drain of the fet so it is turned fully on or off. In order to avoid the problem of npn gain, I would put a resistor in its collector to set the hysteresis. Duke
  18. duke37

    Magnets and science

    Electromagnetic pulses can be shielded with a conductor, silver is the best, copper is very good and aluminium is the lightest. A constant magnetic field can only be shielded with a magnetic material shuch as iron. Look up Faraday cage.
  19. duke37

    Amplifiers

    1. OK 2. You have the divider upside down. The source resistance is lower than the load resistance so the voltage will only be dropped a little. The equation becomes 10k/(10k+200)*20mV. 3. As you say. 4. As Harald says for the second amp etc. It is coming along nicely.
  20. duke37

    Amplifiers

    1. What is the transducer output at room temperature? 2. What will the transducer out be when loaded with the amplifier. A 200 and 10k voltage divider.? 3. What will be the amplifier output when this is amplified? Do the same maths for the second amplifier.
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