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  1. duke37

    Usa Device Repair From Using Uk Voltage

    You will need it looked at by someone who knows. It is often difficult to open the case to see the works. If you are lucky, there will be an input fuse, if not so lucky, the transformer may be burned out and if even less lucky, the circuitry could be fried. You will not be able to get a...
  2. duke37

    Help Making an RF controlled relay!

    You do not say over what distance this needs to work. A wireless door bell may do what you want. It will need a low power supply to replace the door push and the receive end will need a power supply and replacement of the sounder with a relay driver circuit.. What do you mean by a 240V...
  3. duke37

    Please help me with my smps

    The mind boggles. Why have transformers with the windings shorted? What is the circuit to the left of the big capacitors supposed to do? What is the chip, I cannot read the number? Where did this complex circuit come from and what is the purpose of each stage?
  4. duke37

    How to limit bass in speaker?

    The capacitor will need to be quite large. You cannot use a standard electrolytic in this role. You will need a special AC version or a big plastic dielectric capacitor.
  5. duke37

    Name this guitar tube amp component, and do I need it?

    The ECC83 is a dual triode amplifier and I would expect it to be in the preamp or tone control stage. I cannot understand how the amp can work without it unless there has been a bodge. The EL34 is a power output valve, often used in pairs. Two can give 30W with no problem. How many have you...
  6. duke37

    question about a car alternator

    Not all power transmission is 60Hz, were it is 50Hz. Car alternators have a varible frequency output depending on the position of the loud pedal. They run at high frequency to make them small and they have leakage inductance built in. The inductance has a reactance proportional to frequency...
  7. duke37

    240v 100w conversion ?

    Do you mean that you have a 24V (AC or DC?) supply that you wish to convert to 240V (AC or DC?) at a power level of 100W?
  8. duke37

    LPF,HPF,BPF design

    I am not clear as to what you ae trying to do. There is a filter design, which I can not find at the moment which gives out low, medium and high frequencies. There is a problem with your circuit in that the two amplifiers have their outputs connected together so they will be fighting each...
  9. duke37

    some power supply & led question

    You should NOT connect leds in parallel, they should be connected in series with a resistor to make a string. You can connect strings in parallel. Different leds will need different voltages. You can measure the voltage across a led with a meter. Use a resistor to limit the current to say...
  10. duke37

    Magnet passing through a copper pipe

    You said that the drag was due to eddy current losses. The drag will approach zero as speed approaches zero. So the oposing force is not constant. If there is a 200N applied force and 200N drag, then the speed will not change. Why should the magnet stop?
  11. duke37

    Resonance

    Antennas need to be made from low resistance material, silver is the best, copper comes close and aluminium is the lightest. Look around and you will see aluminium antennas on houses fed with copper cable. Magnetic materials are bad news, look up skin effect. What is titanium steel? I...
  12. duke37

    Magnet passing through a copper pipe

    Suppose you have an infinite pipe. Suppose that the drag is 1N/(m/s). Then with 200N push, the speed will settle at 200m/s. If the pipe is short, the speed will not attain balance.
  13. duke37

    Using an arduino relay brick to switch 120 ac volts / 5 amps safely

    Dielectric strength is a property of the material. Condensation will conduct easily especially if there are salts about. Some fluxes contain salts but these should not be used in electronics.
  14. duke37

    Magnet passing through a copper pipe

    Only a guess. The opposing force will go up as the speed goes up, therefore there will be a balance at a certain speed when the drag equals 200N. This may be above or below 100m/s.
  15. duke37

    Calculus I homework question about rate of change of resistance in an RC circuit

    I do not see what the diagram has to do with the problem. Suppose you have a resistor wire dipped into a conducting liquid, the the resistance will go up as the liquid level goes down so you have a way of measuring what is in the tank. Not so daft as it seems at first. You first need to...
  16. duke37

    Calculus I homework question about rate of change of resistance in an RC circuit

    You are right, the resistance will not change. Surely they want either the rate of change of voltage or current.
  17. duke37

    AC Circuit Theory Maximum Power Transfer

    You must calculate the impedance of the source. This will be a resistor in series with an inductor. The load must be the complex conjugate and will be a resistor in series with a capacitor. The two resistors will be the same for maximum power transmission. The inductance and capacitance...
  18. duke37

    Using an arduino relay brick to switch 120 ac volts / 5 amps safely

    It looks to me that the connections have got hot. This will happen if the wires are not screwed down tight. Can you take the circuit out of the humid environment?
  19. duke37

    some power supply & led question

    If 5 leds in series run all right, then stick with this. 5 leds at 2V will need 10V so there is 2V extra to drop with a resistor. Using 20mA, R=V/I then R=100 ohm For 15 leds you will need three strings connected in parallel. Total current 60mA. For 40 leds, you will need 8 strings, giving...
  20. duke37

    Separate Loads turn off and turn on delay

    Many years ago London Transport tried reducing the number of active cylinders on their diesel buses when the full power was not required. The differential thermal expansion harmed the engine. I believe that the inactive cylinders were later cycled but I never heard the result of the experiment...
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