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  1. duke37

    Mackie RC4 speaker no sound

    I do not see a transformer. There is a brown area from the reservoir capacitors, indicating excess current in the tracks. This leads to a capacitor, probably the capacitor feeding the speaker, which looks to have been boiled. Are there any fuses in the circuit? Do you run at absurd volume levels?
  2. duke37

    Variable current power supply with varying duty cycle

    I bought a dual power supply at a junk sale in 2009. This is analog and uses a pair of L200C chips, it controls voltage and current. The L200C could perhaps be a basis of a switched mode supply
  3. duke37

    Capacitor charging itself?

    I did not say the electric field was stored in the dielectric. Where is the energy stored?
  4. duke37

    Capacitor charging itself?

    A capacitor with a solid dielectric has most of the energy stored in the dielectric. If the dielectric is slid out from between the plates, how does the energy get free from the dielectric? Is the energy retained. How are electret microphones made?
  5. duke37

    Measuring forward bias on Motorola 962.3 diode rectifiers with multimeter

    I would think that the bridge is OK. Put a low voltage AC on the yellow connections and measure the output voltage on the black and red pins. The connections have been roughly soldered at some stage. Hopefully no damage has been incurred in the experiments.
  6. duke37

    Variable current power supply with varying duty cycle

    AC or DC?
  7. duke37

    Measuring forward bias on Motorola 962.3 diode rectifiers with multimeter

    Could you show a picture of the rectifiers and where you measured? I would suggest that you are measuring the forward voltage of one diode at 0.5V and two diodes in series at 0.9V. They are almost certainly bridge rectifiers but, if small, could be a ring modulators with the diodes connected...
  8. duke37

    Sewing machine power supply/capacitor blown up

    If this is a capacitor across the mains, it should run without it but produce radio interference.
  9. duke37

    BUCK switching waveform ... problem

    If Q1 turns on fully then the LX waveform should have a flat top at 5V. I thought that Q2 should have a diode across it to take the current while Q2 is turning on.
  10. duke37

    Capacitor replacement the hard way

    Wind the leads around a small screwdriver or drill to make a helix. This can then be slipped over the old lead and can be soldered quickly. This tip was gained from a forum dealing with vintage valve radios, it saves having to unwind the connections on solder tags.
  11. duke37

    What's the working principle of this inverter circuit ?

    One pair of the output transistors need to be turned on when the other pair is turned off so generating an AC drive to the output transformer. In capture1.JPG all output transistors are turned on and off together. There will be no AC on the transformer and the invertor will appear as a short...
  12. duke37

    24v solar panel, have 12v invertor. Wondering if this will work.

    The batteries will become unbalanced if the loads are not identical. One will be overcharged and one undercharged. Better to use a 24V to 12V buck convertor to charge both 12V batteries in parallel or a 24V to 12V buck convertor supplied from the batteries in series to both outputs.
  13. duke37

    Retrofitting a vintage radio for blue-tooth playback. Power problems.

    Unstabilised 6V supply could easily be putting out 9V, hence the smoke! The polarity of the power supply is critical. I would link the two devices through capacitors to eliminate DC shorts
  14. duke37

    Modifying automotive alternator windings...

    Connecting the windings in series will not produce smoke. The current will be the same in each winding.. Take a piece of paper and draw three lines at 120 degrees from each other. Make three pieces of paper with the angles retained. Move these pieces end to end to see the resulting total...
  15. duke37

    How to block Magnetic field coming from substation and underground power to property beside it

    I have just had a couple of MRI scans, I did not notice any physical or mental effects. In order to shield yor house, you will need a complete screen or the field will come in through the doors and windows. Are you going to rebuild the house on top of a super conducting shield?
  16. duke37

    Where did the - 0.7 V from the graph came from? (Diode Clampers Circuit)

    In the second diagram, consider removing the diode. The output will then be a sine wave centred on 0V. Adding a diode limits the negative voltage to about 0.7V and the sine wave is therefore shifted positively. It is still driven with a sine wave but the capacitor allows the average voltage to...
  17. duke37

    Where did the - 0.7 V from the graph came from? (Diode Clampers Circuit)

    The -0.7V is the voltage necessary to turn the diode on when it is driven negatively.
  18. duke37

    Need help modifying ac ammeter (shunt)

    Voltage transformers are happy with no load, they burn out with excessive current when they are short circuited. Current transformers are happy with an output short, they may fail with an open circuit load. The buzzing is due to the core going into saturation. The windings may have failed due...
  19. duke37

    Boost converter

    The amount of charge transferred is dependant on the charge supplied to L1. To reduce this, the signal could be modulated so thet the fet is turned on for a shorter time.(PWM).
  20. duke37

    Boost converter

    I am interested in the simulation in #12 by BobK. The output overshoots on switch on and eventually settles down. Since a certain level of charge is transferred each time, I would expect the voltage to rise gradually to its final value. What is the origin of this apparent oscillation?
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