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  1. duke37

    difference in parameters when circuit switched on and when switched off

    If you have two 60ohms reistors in series, then the voltage will be shared equally between them and the current will be 12/120 = 0.1A. If you have a resistor in series with a bulb, then things are different. The resistance of a bulb varies greatly with its temperature. If you measure the...
  2. duke37

    Comparator inputs

    Put a current transformer in each line, rectify the output curents to get DC, load the outputs with a resistors to get a voltage. Connect these two voltages in opposition and feed a relay through a diode so the relay switches when the voltage A is bigger than voltage B. This might not be...
  3. duke37

    Comparator inputs

    You could connect the two DC voltages in series, one oposing the other, so you have made a comparator. A positive voltage on the output could drive an indicator.
  4. duke37

    Timing coil transistor output to transistor?

    I have not been following this thread but the resulting circuit seems rather strange. You have a diddy 1N4148 feeding in and a fat 1N4007 inside the circuit. Why? What does the 1N4007 do? The input diode stops any negative voltage. If you do wish to have extra protection to the Darlington...
  5. duke37

    1 Mhz oscillator needed

    Look at the CMOS 4047. This will give a square wave with amplitude close to the voltage supply but will have very little current capability. If frequency accuracy is important, then a crystal oscillator is called for.
  6. duke37

    How to wire this AC fan?

    First find your capacitor. It will need to be 1uF, the voltage rating must be for AC and could be higher than on the plate. Second, decide how you wish to connect the wires. I would use a wiring junction box in the UK. Connect the capacitor between green and red. Connect the mains between...
  7. duke37

    Audio preamp problem

    I have never used TINA, I used ECA, a DOS program, many years ago. I used it mainly for heat transfer and vehicle suspension simulation. I have used 5spice once recently but would not be able to tutor someone in its use.
  8. duke37

    Audio preamp problem

    I have not given values of components since the requirements were not given. Perhaps TINA is reliable, I can assure you that strange results can be obtained in practice! If your existing circuit is working just use it. Getting rid of hum can be very difficult. All power supplies should be...
  9. duke37

    How to wire this AC fan?

    Looks like a nice little fan. An AC supply just goes up and down in voltage, it has no specific direction like DC. To get an AC motor to rotate, two (or more) supplies are required with one supply running in front of the other. This gives a rotating magnetic field which the rotor follows. To...
  10. duke37

    How to wire this AC fan?

    I would think that the capacitor is external to the motor as shown in the diagram. With only 1uf, it is probably continuously connected, i.e. start and run. The green and red wires should NOT be connected together, this would short one of the windings.
  11. duke37

    Ultra light / small / bright clip-on LEDs

    Why not use two lines and stuff the power up from the ground. Any voltage loss can be compensated by increased voltage supply. The supply resistance may mean that resistors in series with the LEDs will not be necessary. You can get plastic cord with a stainless steel thread to pass the...
  12. duke37

    How to wire this AC fan?

    The diagram is a little unusual but is clear. You have two wires coming in from the mains on the left. What is the problem? The capacitor is 1microFarad 220VAC working and should be rated for continuous duty.
  13. duke37

    Audio preamp problem

    You have not said what R1 is for. You have not said what gain you want. You have not said what the source impedance is. You have not said what the load impedance is. I attach a diagram of a two transistor circuit which will have a high input impedance and a fairly low output impedance. The...
  14. duke37

    Audio preamp problem

    The input resistor also looks strange to me, perhaps it is to provide power to the previous stage. Negative feedback can increase or decrease input impedance. In this case, the input Z of the transistor will be low also the feedback in anti-phase will reduce it further. If the gain of the...
  15. duke37

    Audio preamp problem

    R2 produces negative feedback so the input impedance of the transistor is low. I would guess that it is about 1k. This will give a high pass filter with the 100n input capacitor with a cut below 1kHz. If you have a low impedance source, you could just increase the capacitance. To reduce...
  16. duke37

    HiPot Selenium Rectifier \ Diode Replacement

    These are rectifiers used in colour tv LOPT stages to produce the EHT. They have many little rectifier pucks inside the tube to in series to get the high voltage capability. High voltage silicon diodes are available, I tried RS but, as usual, got lost in their website. On the first links you...
  17. duke37

    Does this Circuit make sense?

    I do not have a doll's house, I use these bulbs for the dial lights in valve (tube) radios. Using a 8V bulb on the 6.3V supply means that the bulb gives less light but lasts forever. The variation of resistance with temperature can be used to stabilise the output voltage of a Wein bridge...
  18. duke37

    Does this Circuit make sense?

    A 8V 0.15A (1.2W) bulb measures 10ohm on my analog meter which rises to 18ohm in a few seconds as the filament warms. The running resistance would be about 53ohm so resistance ratio equals 5.3.
  19. duke37

    Help me on this circuit formula pls

    That is the voltage drop across the resistors but you have forgotten to include the batteries.
  20. duke37

    12v dc to 6v dc 100w converter

    A CMOS 4047 will give outputs to switch a couple of FETs alternatively. A transformer can be wound on a TV LOPT transfomer core to give the lower voltage. If the transformer is wound as an auto transformer and AC is used to drive the light, then losses would be low (no rectifiers, no output...
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