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  1. duke37

    Advice please.

    I may be able to find a lead from a US ghetto blaster. I do not know whether it had an earth. I have got my neighbour looking for it. Would you be interested?
  2. duke37

    Potentiometer Resistance ?

    This is a suggestion for crude motor speed control. When the slider is at the bottom there will be no voltage on the transistor and so no collector current. When the slider is at the top, there will be 5.5V across the 1k resistance so about 5mA base current. If the transistor has a gain of 100...
  3. duke37

    IR/UV Light

    Do not run LEDs in parallel without individual current control.
  4. duke37

    Electrolytic capacitor in timing use?

    I do not see an electrolytic capacitor of any value across a base/emitter junction. C3 is 1nF C7 is 10nF There is no 10µF These can be plastic film types. (polyester ot polypropylene)
  5. duke37

    Bridge Rectifier Output ??

    You have something very wrong if the rectified voltage is so low. you are very likely to have something fail if run like this. Show us a circuit diagram of what you have made so we can comment. You do not need a controlled voltage to drive leds unless you need a controlled light output.
  6. duke37

    Potentiometer Resistance ?

    You have not said what current the motor takes. You have not said how stable the speed should be. A potentiometer is normally a small component and will fail if too much power is dissipated by it. It would be better to use the potentiometer to set a small current to the base of a transistor...
  7. duke37

    sw radio

    The crystal set takes all its power from the aerial. The power can only be extracted efficiently by inserting the set between aerial and ground. Sets with amplifiers can manage a much smaller input. The connection will be to the common line in the set, often termed ground. You could show us a...
  8. duke37

    Schottky Diode

    The voltage change across a capacitor is given by the equation dV/dt = I/C If my calcs are correct, then a 5V ripple at 150A and 50Hz will need 4.5F. This is impractical for an impecunious student. I am not sure about the need for a stable voltage. Cheap welders use leakage inductance in...
  9. duke37

    Schottky Diode

    Now you are beginning to talk turkey. The reference says the diode bridge is suitable for welding so I would go for that. Note that you will need considerable heat sinking, perhaps fan cooled.
  10. duke37

    Timer circuit to control coaxial switch

    If all you want is change over, then you will need to energise one or other of the control lines. This could be done with a 555 and a transistor to invert the output to one line. A 555 will need a much higher voltage than the relay requires so some attenuation would be necessary. A CMOS 4093...
  11. duke37

    Schottky Diode

    You are likely to get much more than 100V spikes with a welder. The schottky diodes may not like this. They should run much cooler than standard diodes. The first circuit you show only passes current for half the time. The arc could go out during the other half of the cycle. There is...
  12. duke37

    Linear power supply design

    If you are using less than 1A, you do not need a booster transistor. The TIP42A is the wrong way round.
  13. duke37

    Electric motor heat question

    If the motor is dissipating 140W it will burn out unless it is big. You need to find the voltage and current when stalled to get the power dissipation. It does not matter what is stalling the motor.
  14. duke37

    help no heat

    You will need to give more information. What is a ymgi mini split system. What country are you in? Can you supply pictures of the equipment and the faulty board?
  15. duke37

    Linear power supply design

    The electrolytic capacitors are used to smooth low frequencies but they are ineffective at high frequencies so they are paralled with small low inductance capacitors. Why do you need over 1A (or 40V) to drive a preamp circuit?
  16. duke37

    Bridge Rectifier Output ??

    The voltage will not be stable and will vary with the load. For calculations you will need to use a high voltage if the load is low and a lower voltage when the load is high. Voltage regulators are used after the capacitors to give a constant voltage for voltage sensitive circuits.
  17. duke37

    number of coils to a generator.

    ]In Canada the mains frequency will be 60Hz so an alternator with just three poles, one for each phase will need to run at 3000RPM 3600RPMif connected to the mains. You can use more poles to give a lower speed but the alternator will be bigger. I would suggest that you get the turbine running...
  18. duke37

    Electric motor heat question

    The torque will be roughly proportional to current. PWM can be used to set the mean current. A 50W output motor running at 80% efficiency will be dissipating about 10W. If you stall this motor and dissipate 140W it will not last more than a few seconds.
  19. duke37

    Microscope capacitor exploded

    It is not an electrolytic capacitor, it is far too big for that. I would think that it is too small for 1µF so would say 0.1µF. As has been said there are X and Y rated capcitors for use on the mains. I do not see where you have stated the mains voltage or frequency. If you have 250V mains...
  20. duke37

    Microscope capacitor exploded

    The capacitor looks to be close to the input switch so may be a suppression capacitor across the mains. i do not know what the M means, if it were a resistor it would be a 20% tolerance. I suggest that you replace with a modern 600V or 1000V capacitor. The bulb failing may be due to a...
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