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  1. duke37

    Parameters needed to design a Butterworth filter?

    This is a difficult one. You must decide what filtering you want and this will decide the type and complexity of the filter. If I remember rightly, there should be no ripple with a Butterworth filter. I have a book 'Electronic Filter Design' by Arthur B. Williams. I could look up a design...
  2. duke37

    #5000

    Congratulations. You have been a stalwart member of the forum.
  3. duke37

    Pot Core dismantling

    I do not have photo equipment at present to take a picture. The pot cores I have tried to open all seem to shatter, the glue is as strong or stronger than the ferrite. The present one I would like to dismantle is out of a Kestral electric fencer and is used as a blocking oscillator with a...
  4. duke37

    Pot Core dismantling

    What is the best way of taking a used pot core apart? I have tried the big hammer method, I have not managed to dismantle without detroying it. It would be nice to save the bobbin so that the number of turns can be counted.
  5. duke37

    AM/FM Modulator

    People make very low power transmitters to use with old medium wave radios. These produce an AM signal only. Look up pantry transmitter. AM can be seen on a scope and the modulation depth can be measured. FM would be difficult to see on a scope since the amplitude is constant. You could...
  6. duke37

    CRT High Voltage Power Supplies

    It would be very inconvenient to have the deflection electrodes at a few thousand volts. The drive amplifiers need to be directly connected to go down to DC. Z axis modulation on my scope is AC only and fed through a capacitor. I have not made a TV but perhaps you could investivate the circuit...
  7. duke37

    CRT High Voltage Power Supplies

    Televisions use a high positive voltage to energise the screen. The beam deflection is magnetic with scan coils which are insulated from the high voltage. The cathode needs to be close to earth to allow variable brightness. Oscilloscopes use electrostatic deflection and the deflection plates...
  8. duke37

    External Thermometer for Dry Iron

    A dimmer switch would work if it were capable of providing the current that the iron requires. A diode in series with the supply will halve the power and diodes of sufficient capability are easy to obtain. The diode could be switched either manually or when the iron is lifted from its stand to...
  9. duke37

    automatic dark sensor

    A resistor across C2 will dump some of the input current and reduce the dissipation in R3 and the Zener. Replacing R6 with a Zener will increase the amplifier gain. Investigate the effect of R5 and R7 to get it to operate the switch. Do your experiments with a 9V battery. I do not see the...
  10. duke37

    FM radio with impedence 5 Ohm output

    If it is an old radio, it will have valves, if it is newish, it will have transitors. A valve radio must have a speaker load or things can go horribly wrong. Put a resistor, 5Ω to 10Ω across the output and put a potentiometer, 100Ω to 1000Ω across this and take the output from the ground...
  11. duke37

    FM radio with impedence 5 Ohm output

    Depends what you mean by PC speaker. These often contain a powr supply and amplifier. All you need is the basic speaker. If you wish to use a PC speaker which takes its signal from an audio card, then you will need to attenuate the signal from the radio.
  12. duke37

    Wind powered generator using radiator fan?

    Another problem with brushed PM motors is that the cheaper ones have the rotor windings in slots parallel to the rotor axis. This means that the motor will jerk from one slot to the next, this is known as cogging. A certain amount of torque is required to start the rotation and there will be a...
  13. duke37

    Low voltage drop 8 amps Ac to DC power converter

    Rough calculation - The voltage across R1 will be the emitter/base voltage of the TIPs (0.7V) plus the voltage across R2 to R4. Thus at 3A output the voltage across R1 will be 0.7V + 0.1V = 0.8V. The current through R1 will be about 50mA. With a 14V transformer you should get up to 19V...
  14. duke37

    Relationship of frequency and capacitance.

    I think that the book refers to the operation of an oscillator using a tuned circuit. The frequency is 1/(2*pi*sqrt(L*C)), thus the bigger the capacitor, the lower the frequency.
  15. duke37

    Wind powered generator using radiator fan?

    I have used an old radiator fan motor to drive a coil winder. I used the back EMF to measure speed so it could be used as a generator. It had a permanent magnet and brushes. I would think that brush friction would be a problem in your application. The torque generated by a small fan would be...
  16. duke37

    Transformer trouble

    R5 does not maintain a steady voltage across the primary, it maintains a very, very small current. In order to get a decent amount of output, you will need a buffer amplifier to provide the power and a single tuned transformer (not double tuned). Why are you using tuned circuits? A similar...
  17. duke37

    Best brands of pots?

    The first electronic organs used mechanical pots for volume control but these wore out and were noisy. They were replaced by a bulb running on DC and a foot operated shutter to alter the light shining on a light sensitive resistor such as an ORP12. I have never used a Hall effect device but...
  18. duke37

    Help Me Understand This Inverter Circuit

    The dropbox does not work for me. If you run a transformer on double its rated voltage, you will need to double the frequency to limit the core flux.
  19. duke37

    Best brands of pots?

    What does the pot do? If it needs to operate many times, you could consider a light shutter or Hall effect device for greater reliability.
  20. duke37

    dc-cdi 12/220 issue

    Frequency check from? The 4047 data and a slide rule.
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