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  1. duke37

    9v Guitar Amp w/out LM386

    The emitter's voltage must be around half the supply voltage. Get this right first.
  2. duke37

    9v Guitar Amp w/out LM386

    The emitters of Q1 and Q2 should be sitting at 4.5V. If Q2 is too hot, then this voltage is too high. R2 is the feedback and could be adjusted to achieve this but the voltage will be temperature dependant.
  3. duke37

    magnetic switch/connector

    I would use one magnet and a reed switch. A reed switch is a sealed glass tube filled with a vacuum or inert gas. It has a two reeds fitted, one from each end. When a magnet is near, the reeds are pulled together, completing the circuit. The reed switch is only suitable for low current...
  4. duke37

    Watering system

    I repaired a rain sensor many years ago for someone in the sunny south. It was corroded and the wires had dropped out of the seized connectors. The connectors were replaced and dosed with Waxoyl. The sensor consisted of strip board with alternate strips connected to the cable. It apparently...
  5. duke37

    AM modulation

    @Yap I think you have things about right. It is possible to analyse an AM signal to look at the frequency components. This is done by Fourier analysis. All the frequencies are transmitted as radio frequency just like any carrier. If you access the radio at the secret nuclear bunker near...
  6. duke37

    AC adapter not working, strong burning smell

    The diodes appear to have overheated and burnt the circuit board. This could be due to a faulty reservoir capacitor or excessive load current.
  7. duke37

    Wireless relay

    How about an adapted wireless door bell?
  8. duke37

    Battery charger repair

    The diodes will not be epoxied on. The epoxy will not conduct electricity and will be poor thermal conductor. The original rr50 diodes are available at a reasonable price. They seem to be clamped to a backing strip with a spring to take account of thermal expansion. I do not know what your...
  9. duke37

    Battery charger repair

    There is nothing in your picture that can pass 50A, looks more like 5A to me. Does it work? You will need an external resistance such as a bulb to control the output current. Do not use 1/2 wave rectification, this will put the transformer into saturation which will burn it out. The original...
  10. duke37

    Fan motor: brushed or brushless

    The pole pieces look to be asymetrical to get rotation at start.
  11. duke37

    Active narrow band-pass filter design

    The circuit is the same as shown in Electronic Filter Design Handbook by Arthur B. Williams so should work. I use LTspice to simulate circuits. The LM318N is a high speed op-amp and needs a positive and negative supply which is by-passed. People hate the slow speed 741 but you could try one. I...
  12. duke37

    Heater Fan - Remote Activation with Relay or wireless? 94 AC Supply Voltage

    I have some Norslo 240V AC 2 pole change over relays and did some measurements on them. Resistance 7k5. AC 50Hz 130V pull in, 130V drop out. Feeding with a diode. Pull in 110V, drop out 75V Feeding with a diode with another diode across the coil. Pull in 90V, 20V drop out. It seems that...
  13. duke37

    Transformer's terminals according to the schematic

    You are welcome, I enjoy helping people it gives me much satisfaction.:)
  14. duke37

    How would I go about making a program that controls spark plug(noob)

    There is a thread which has been going for years with hundreds of replies. It deals with ignition for a 2-stroke engine. You should state what you want to do, not 'a have a hammer, what should I hit'.
  15. duke37

    Transformer's terminals according to the schematic

    Do not connect the secondaries until you have the primary running with no faults. Measure the secondary voltages to determine where the secondaries are to be connected. Go gently, bit by bit. Looking at a different transformer is only going to confuse you.
  16. duke37

    High Current DC Switching

    You may be right but how did you determine this? Normally, two cold contacts will not spark until they are very close. When they open, an arc is always generated and if the inductance is large, a lot of energy has to be dissipated.
  17. duke37

    Transformer's terminals according to the schematic

    The primary consists of two windings connected in series. These have the same number of turns but a different wire diameter. The lowest resistance winding will be the 110V winding and the higher resistance winding will be for 220V. Al the secondary windings are two terminals only and the...
  18. duke37

    Project for interested novice that will give him most taste of electronics?

    I learned by starting with a crystal set and also by mending things, such as electric fence energisers and electric drills. I did the course to qualify me as a radio amateur and then used my knowledge for defining instrumentation at work. Now I enjoy fault finding and repair of valve radios. It...
  19. duke37

    Transformer's terminals according to the schematic

    Nice pictures. L6 looks to be a winding connected at one end only to act as an interference screen between primary and secondary. It should be connected to the core. This will give an indication of the order of the primary connections. C904 is shown as connected to one end of the primary but...
  20. duke37

    Transistor voltage measurement

    The circuit will have a ground connected to many stages. Measure the voltage between ground and emitter. Measure the voltage between ground and base. Measure the voltage between ground and collector. Some subtraction will give the voltages required. With an npn transistor, the voltages...
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