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  1. duke37

    reparing Receiver - TX-8511

    If the A speakers worked OK, then failed and the B speakers worked for a while, it is unlikely to be a fault in the electronics. I would think it is a dirty switch. Spray with switch cleaner or wash with isopropyl alcohol.
  2. duke37

    Coils

    I do not see how a magnet can cycle up and down in a torroid. Do you mean a cylinder? There is a limitation to the size of the coil. You should fill the available space for the best efficiency. You can use lots of turns of fine wire with low current or a few turns with thick wire and a lot of...
  3. duke37

    why 1K resistor

    They limit the base current to a safe value.
  4. duke37

    Smallest Rocker Switches available (with LEDs)

    I only have old catologues from RS and Maplin. RS do rockers 21*15mm Maplin do toggles which can be spaced 10 or 12mm. You will need to look at the various catalogues.
  5. duke37

    Smallest Rocker Switches available (with LEDs)

    Have a master switch with a beacon, then you can use small unlighted switches.
  6. duke37

    Unregulated power supplies

    Many things come in TO-220 style. This could be a 5V regulator which could overheat if the input voltage is too high. A circuit diagram would help. The higher the current capability of the wall wart, the cooler it will run.
  7. duke37

    a simple noise filter, L or C

    Your + and - supplies need to be very well smoothed as any variation will be fed directly to the 5pF capacitor. A large capacitor on the negative divider would help.
  8. duke37

    Unregulated power supplies

    The 6V supply would almost certainly be safe but the voltage may drop too low under load. The 9V supply looks dodgy but could be used with an added-on regulator (LM317T) which will need a substantial heat sink.
  9. duke37

    a simple noise filter, L or C

    Sorry, I just assumed that the voltage supply at the top of the diagram was positive. Once you have gone through the fet buffer, you have a low impedance source and a load of 1M will not affect it.
  10. duke37

    Old overhead projector blowing bulbs, diode issue...

    You can normally check a diode with a meter, they will either be open circuit or shorted. In your case a shorted diode will give too high a voltage If it is a diode, which I am not sure, then a 400V 10Amp diode would do. It would need to be in the same configuration to fit to the heat sink...
  11. duke37

    DC Shunt Motor

    A very good point. It will never happen because there will be friction to slow the armature down as I pointed out. The only thing perfect in this world is me !
  12. duke37

    a simple noise filter, L or C

    I do not see how the ions will go to the plates without a potential to attract them. To get a turn over frequency of about 10Hz, you need an R*C time constant of 0.1sec. Use C=100nF, R=1M. I believe that fets have high low frequency flicker noise.
  13. duke37

    a simple noise filter, L or C

    I do not see where the DC signal comes in. What frequency do you want to eliminate?
  14. duke37

    DC Shunt Motor

    The shunt winding produces a magnetic field. The armature is the rotating part. There is no difference between a motor or generator in this configuration. If the armature is rotated in the field, it will produce a voltage (back EMF). If this voltage is below the applied voltage, the motor...
  15. duke37

    Difference between DC motor & Stepper motor

    Not quite, a normal DC motor has a commutator which switches the current in the armature as it rotates. The magnet is on the outside. A stepper motor switches the current with external circuitry, the magnet is on the inside. Some DC motors are stepper motors with built in circuitry to...
  16. duke37

    ground to increase cooling capacity of heatsink?

    To get good heat conducton, you need a large area and a short distance. A wire has a small area and a long distance. It is often insulated which will impede the conduction to air. To get better cooling, the heat sink can be colled with a fan or the case of the equipment can be made the heat...
  17. duke37

    4536 Programmable Timer question

    Looking at the data, the binary inputs are to set the division ratio.
  18. duke37

    need help to understand a circuit

    As you say this is a current controller. The current is switched with Q5 and Q6 to define the current in the bases of Q8 and Q9. The zener makes the current constant even if the supply voltage varies so the circuit can be used on a wide range of voltages.
  19. duke37

    Inductor - 4 Pins???

    88mH pot cores used to be used to load telephone lines and many became available on the surplus market. They were often used to make audio filters for RTTY.
  20. duke37

    Band-Pass Filter Help

    If you are using LTspice you can fatten the lines so they can be seen.
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