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  1. duke37

    I need help in connecting a transistor to the battery terminals

    Elecrolytic capacitors ARE polarised and must be connected the right way round. The transistor is connected the right way round but if it is connected direct to the battery there is likely to be smoke when it is turned on.
  2. duke37

    Confused about transformer windings

    Connecting the primary windings in series should be OK but they MUST be connected correctly. The secondaries can be connected in parallel if the transformer has been made to have identical voltages. If the voltages are not identical then one winding will feed power into the other. They MUST...
  3. duke37

    A SIMPLE RADIO RECEIVER

    That looks like a good site, I would go for the MK484 circuit with transistor amp to drive modern headphones.
  4. duke37

    Older Shunt Gear Motor and dc controller

    A permanent magnet motor uses a permanent magnet (surprise, surprise) to supply the static magnetic field. A shunt motor uses a winding to make an electromagnet. No field current, no magnet, no torque, no speed. Find the two wires which feed the field, they may have a resistance of 1k or so...
  5. duke37

    Solar Panels in uk

    My Maplin 2011/12 catalogue has lots of solar power kits of various sizes.
  6. duke37

    Back EMF in Solenoid

    I do not know what you mean by leakage reactance. The solenoid will have reactance. The current in an pure inductance will be out of phase with the voltage. So, when the voltage is at maximum, the current will be zero and will gradually build up. When the voltage has got to zero, the current...
  7. duke37

    Relay configure trouble

    To hold the relay on, you need another contact which is made when the relay is pulled in and provides power to the relay coil.
  8. duke37

    Need help solving battery mAh question..

    It can be right. The motor generates a back EMF when it is turning which is proportional to speed. Thus a motor running on 12V may be producing 11.9V back EMF. The current taken will be 0.1/R. The slower the motor runs, the less the back EMF and the more current.
  9. duke37

    A SIMPLE RADIO RECEIVER

    We all do this for fun. I would suggest that you start with a crystal set, using a coil, capacitor, germanium or Schottky diode and a set of high impedance phones. The power comes fron the antenna so needs to be long, say 50m. Then go to an amplified crystal set using your transistor but a...
  10. duke37

    Relay configure trouble

    Do you want the relay to latch on?
  11. duke37

    Allow only one motor to start, at any given time

    According to my abacus, 2 HP = 1892W 1892W on 120V is 15.8A So, you can only run one motor on this supply. Motors can take up to 8 times full load current to start so even one may be too much depending on the motor and trip mechanism.
  12. duke37

    Hunting light

    Show us what you have. It should be possible to change it over.
  13. duke37

    Amplitude and Frequency

    Dave You are right, a sine wave would be best but I wonder if it would be any more efficient than a square wave. A sine wave would need a sine wave oscillator (Wien bridge?) and a class B amplifier with perhaps 60% efficiency. A square wave could be generated with a 555 or 4093 with only...
  14. duke37

    question about radio parts

    AM and FM radio are somewhat different but all radios have a means of controlling the gain so that the sound level will be similar even if the received signal strength varies greatly. This control , the AGC or automatic gain control, can be used to drive a signal strength indicator. An AM...
  15. duke37

    Amplitude and Frequency

    What square wave will you be adding? The glass will resonate at a certain frequency, you should make an experiment to find out what this is. Once you know the frequency, you can make an oscillator and chose a transducer to generate the sound. You can generate a square wave, sine wave or...
  16. duke37

    Amplitude and Frequency

    Here is a picture of an acoustic parabolic mirror. Not very portable ! :):)
  17. duke37

    9.6VDC,3.3Ah power want to convert to the AC power

    It is strange that your machine is so sensitive. A silicon diode will drop about a volt so you could try 2 diodes in series with one power lead. The diodes will need to be connected in the forwad direction. Chose 5A or more diodes, they may need to be fixed to heat sinks.
  18. duke37

    Amplitude and Frequency

    The wavelength can be large. Bottom C organ pipes will be 32ft long for half wave but a piccolo is only a few inches long. The speed of sound is about 340m/s so the wavelength at 6800Hz will be 340/6800 = 1/20 or 50mm (2 inches). Quite within the possible range of a parabola. Perhaps...
  19. duke37

    Amplitude and Frequency

    If you run a damp finger round the rim of the glass, you can get the glass to resonate so you can determine the frequency needed. The sound level can be quite high. To make the glass break, you will need a level mucch higher than this and very accurately matched in frequency. It may take several...
  20. duke37

    Amplitude and Frequency

    If the wine glass is to break, you will need a high quality thin wall glass not a thick chunky one. It will only break when driven at its resonant frequency and it will take time for the vibration amplitude to build up. The Q of the glass will be high so the driving frequency must be...
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