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  1. duke37

    VOLTAGE ISSUE?

    A silicon diode will drop something over 0.6V when conducting in the forward dirction, it does not act as a resistance. It does not conduct in the reverse direction. You do not say what the battery voltage is that you have to reduce to under 12.8V.
  2. duke37

    Strange sound

    I have never used Audacity but I was told that it will do Fourier transforms. This will tell you the predominant frequency of the waveform and hence whether it is mains or switch mode power supply.
  3. duke37

    Battery charger only putting out 9 volts instead of 12?

    Your charger may be working correctly. Without power, you can check the diodes by measuring the voltage drop across the output using the resistance range. If there are four diodes, the drop should be about 2V. An AC source has a varying voltage. The voltage quoted is normally the RMS voltage...
  4. duke37

    Adjustable controller

    The devices probably switch between full and off so could be on full together even when warm. If you can find a plug in phase angle control for the bigger device, then this would be the safest way to reduce the load. Here in the UK 5A lamp dimmers are common so could be used on the 700W...
  5. duke37

    galvanometer of wheatstone bridge

    More or less but when the bridge is balaced, there is no voltage across the bridge so no current and the resistance is not significant.
  6. duke37

    feedback circuit analysis

    A very strange circuit. Are you sure that the two RF resistors are connected to ground?
  7. duke37

    Overhauling High voltage PSU

    The pass tubes should be matched if you are going to run the PSU to maximum. You should find out why the filament went open circuit. Why replace the oil insulated capacitors? If you put electrolytic capacitors in series, they will need parallel resistors to equalise voltages. 30MF seems...
  8. duke37

    Old stereo amplifier, right channel gives weak signal and keeps disappearing

    You have two channels which should be similar. Get a piece of wire with a crock clip on each end and connect across similar points. I would start at the volume controls. If the output is different, then there is a fault after the volume control. You can also connect the two inputs together to...
  9. duke37

    0-10V DC Signal

    Measure the voltages when the boiler is connected. Have you got the polarity correct? Much more obvious if you use an analog meter.
  10. duke37

    Crystal accuracy

    There are many orientations of the crystal. A capacitor is used to trim the oscillator to the correct frequency and then an orientation is chosen to give minimal frequeny change with temperature. If high accuracy is required, then an orientation is chosen with minimal frequency change at an...
  11. duke37

    [Amplifier][13,56 Mhz][ ~ 15 dB] Transistor IRFD110 - does it work?

    In #3 I asked whether the transistor in the simulation included capacitances. I have not had an answer yet. You say that what you are doing is not that difficult but I think you may need feedback, neutralisation or unilateralisation. Making a RF amplifier is not easy, it may even turn into an...
  12. duke37

    10 stages of different gains, output voltage is momentarily 1 volt

    If the output voltage is low, the first thing I would look at would be the power supply. It is very stange that the output is in steps of a tenth of a volt to an accuracy of one part in a thousand. Without a circuit diagram it is impossible to for me to give further advice.
  13. duke37

    Ammeter adjustment / shunt

    You will need a voltage reference of 9.5V. The meter will need to be connected between this voltage and the voltage to be measured, in series with a resistance to add up to 65k75. If the source voltage has a significant source resistance, the meter series resistance will need to be reduced...
  14. duke37

    DC supply without transformer

    Any value of C1 should give you 5V, it will depend on load. C1 has a fairly high impedance at your unknown mains frequency. Thus this controls current. When the current passes one way it takes current from D1 and in the other direction, it pushes it through D2. This current is smoothed...
  15. duke37

    newbie question

    The diode voltage can be as high as you like. 100v would be fine. The diode current should be bigger than the load current, in your case I would go for a 10A diode. A silicon diode will drop about 1A (look up the specification) so will dissipate 5.5W and will need cooling such as bolting...
  16. duke37

    Powering a flyback transformer

    Please tell us the objective of your project. Is a flyback transformer a TV line output transformer (LOPT)? What power is the speaker amplifier?
  17. duke37

    How do I fix this "blown" pcb area?

    I have not seen a fuse labeled as shown. T is normally for time delay or slow blow to allow capacitors etc. to charge when switched on. 250V is the maximum voltage that the fuse should be subjected to. Higher voltage fuses will be longer and have ceramic bodies to resist the arc.
  18. duke37

    How do I fix this "blown" pcb area?

    One rectangular block block is labelled CP24 so is probably a capacitor in the power section. The printed circuit track could be linked with a strand of thin wire. Most flexible cables are made with wire of thickness 0.0076 in or 0.2mm. This has a fusing current of about 6A so you could use...
  19. duke37

    Help with tv repair

    It looks as if the 12V rail is being pulled low and the PSU is trying to compensate and the 24V rail is rising.
  20. duke37

    [Amplifier][13,56 Mhz][ ~ 15 dB] Transistor IRFD110 - does it work?

    What does D1 do? Is it the wrong way round? Does the Multisim transistor model include capacitances?
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