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  1. duke37

    Home stereo compatible with 12v campervan?

    A rusty earth connection can do that.
  2. duke37

    JVC Speaker getting power but not producing sound

    What do you mean by 'getting powe'. Some speakers come as a pair with power going in to one box to supply an amplifier which drives both speakers. If the speakers are the more powerful type with just a red and black lead going in, take an analogue meter, set it to the lowest range and measure...
  3. duke37

    Why are mains plug pins usually made of brass in the UK?

    Zinc is cheaper than tin so brass is cheaper than bronze. Brass with a little lead will machine easily. Copper is too soft unless alloyed with toxic beryllium. The overheating of the UK plugs is often due to poor connections to the inbuilt fuse. At one time I worked for an electrical company...
  4. duke37

    How to connect op amps in parallel

    You can sum with resistors to a common point. If you make this point at the -input of the op-amp, you will have a virtual earth amplifier. The current going into this common point will carry on through the feedback resistor and so will generate a polarity reversed voltage. One input will not...
  5. duke37

    Homemade 555 Tachometer

    If you want something simpler, go for the LM2907, it has a regulator built in so you do not need the 7805. It is also designed to work from the dirty 12V supply of a vehicle. The TI data gives application circuits. One of the reasons we are confusing you with facts is that you want to change...
  6. duke37

    Homemade 555 Tachometer

    The 555 produces a fixed width pulse for every trigger pulse. The meter measures the average voltage through RPM CAL. Thus if there are twice as many pulses as required, then the resistor will need to be twice the value. If the input pulse comes too soon to get a complete output pulse before...
  7. duke37

    Transistor amplifier configuration for transmitter antenna

    Valve transmitters use a PI match circuit between the valve anode and the 50Ω load. This allows the valve to feed into a high impedance for efficiency. Transistor output usually uses a grounded emitter amplifier and needs to provide the transistor with a low impedance load. Normally, an LC...
  8. duke37

    Understanding RF Signals

    In the UK, the RSGB does courses for the radio examinations. The novice examination starts at the very beginning ans includes some practical skills.
  9. duke37

    Homemade 555 Tachometer

    The meter does not need to be different, just adjust RPM CAL to suit. Reduce C2 by half to allow higher trigger speeds if necessary. You may be able to get a signal by capacity pick up but will need experiment. I would increase R1 to perhaps 100k to protect the 555. Do not use a CMOS 555, they...
  10. duke37

    Help needed with old components

    j380 P channel 100V 12A 2SK2931 N channel 60V 45A What makes you think they have failed? They do not look to be mechanically damaged and have not been removed for testing. With a 12V supply (guess) they will pass 4A through a 3Ω coil, well within their ratings.
  11. duke37

    Help needed with old components

    The 2SK2931 is an n channel powerful fet. There is a reason why these fets failed, presumably they drive the motor. There would be no point in putting in a couple more fets to fail. I would look at the motor if that is what they drive. Why the secrecy?
  12. duke37

    Help needed with old components

    Show us the circuit. I Googled J380 and found that it is a P channel powerful fet. Have you looked up the others? Why do you wish to find the components when you already have them?
  13. duke37

    Easy Machine To Wind Transformer

    That is my problem.:) A sewing machine motor with foot pedal will be powerful enough to wind thin wire. A motor enables hand feeding to be more accurate. I have just wound 30,000 turns for a solenoid for a slave clock. A counter is very useful, you do not want to start again after 10,000 turns...
  14. duke37

    Capacitor In Line?

    18V at 0.5A is 9W. quite a lot of heat to get dump. You would be better to use a regulator set to 18V so dropping 10V or less depending on the load. What is your load?
  15. duke37

    Model Ship LED Project

    One way of connecting a wire to another is to wind a pigtale in one wire and to slip the other inside and solder. Use heat shrink tubing for insulation and neatness. I use a small watchmaker's screwdriver as the former, it is strong enough to resist bending. I use this method to replace...
  16. duke37

    Choices for stepper motors and off the shelf drives and rectifiers

    Can you skim the commutator, taking off minimal material with a very sharp tool? Do not use any emery paper on the commutator. Can you find brushes that fit? Check resistance between each commutator segment. If there have been sparks between segments, then the outlook is poor. A picture would help.
  17. duke37

    How to connect tweeter with speaker, series or parallel?

    The circuit shows the drivers connected in parallel. The bass driver will take much more current than the tweeter. Connecting them in series may well produce smoke. The capacitor is to steer the high freqency signals to the tweeter and keep low frequencies out. Nice pictures.
  18. duke37

    Digital clock

    It can be done but is hardly worth while unless you want to do it for fun. This would be done by transforming to DC and then using a free running invertor to generate 110V 60Hz. The frequency may not be sufficiently accurate. One way is to make a 300Hz oscillator which is phase locked to the...
  19. duke37

    Digital clock

    The clock probably uses the AC supply as its frequency reference. The supply in the US is 60Hz whereas I think you have 50Hz so the clock will run slow at 5/6 the rate. Also it is not clear what you convertor is. If it is just a transformer (likely) there is nothing you can do about it.
  20. duke37

    12v Automotive Cooling Fan Indicator Light

    A diode allows current to pass in one direction and not the other. A diode in series with the motor will stop back feeding but will drop about 1V. However, 11V should be enough for you. The diode will need to be fat enough to pass the motor current, 5A should do. A convenient place would be the...
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