Search results

Search Forums New Posts
  1. duke37

    What readings to expect from a DMM's Cap setting

    Capacitors A to E are DC electrolytic capacitors. The meter often uses time to charge to a low voltage. Leakage can affect the results. Capacitor F is a foil AC capacitor and will not leak in a similar way but may have a high value discharge resistance across it.
  2. duke37

    Anti surge on motorbike

    There are buck/boost convertors about which I know not. These should control the voltage.
  3. duke37

    50Mhz Square wave generation.

    To measure capacitance you do not need a square wave, a sine wave would do. To get a square wave you need lots of odd harmonics so if only going to the 5th harmonic, the circuit must be able to handle 250MHz without phase distortion.
  4. duke37

    Vizio tv repair

    Send it to davenn, they live upside down there.:)
  5. duke37

    Power inverter AC Output

    Square wave? Modified sine wave? True sine wave?
  6. duke37

    In need of help with AC motor!

    Ifr this is an induction motor it will not make a generator unless it is coupled to a stiff AC supply.
  7. duke37

    How fragile are diodes? Can you screw them up soldering them?

    Not quite, plumbers use 40Sn/60Pb, a lot different to eutectic solder.
  8. duke37

    Relay problem (buzzing noise) on motor and solenoid control board for hydraulic bath

    I knew a Robert Hill from Derby - nice chap. A relay may drop out if the load is too high for the power supply to hold the voltage up. A typical case is the starter solenoid on a car but it bangs in and out rather than buzzing. Measure the power supply voltage. Edit :)It is upside down...
  9. duke37

    Relay problem (buzzing noise) on motor and solenoid control board for hydraulic bath

    If you can hear buzzing, it seems as if the power supply is not behaving properly. This will also explian the reduction in motor power. I doubt if it is a relay problem.
  10. duke37

    Suggestions for a mobile power source for a guitar amp? Car battery, etc?

    It is fairly easy to make a DC to DC invertor to give whatever voltage is required. My latest one was to give 350V for a transceiver. I used a TV line output transformer core with one turn/volt and a couple of fets.
  11. duke37

    5 decade old battery pack bridge

    Since you do not wish to do any work, read this. Input voltage 115V at 60Hz? Load drop about 12V+ so 100V across the capacitor.. Reactance = 1/(2*pi*f*C) Current = voltage/reactance = 100*2*pi*60*0.56E-6 = 21mA Dirty mains with harmonics will give a higher current. I do not worry about what is...
  12. duke37

    Step down transformers

    You will not get constant current if you increase the loading, the current will rise and the voltage will fall. The efficiency could well drop so there will be more heat in the transformer and you will not get the output current you want. The efficiency of an unloaded transformer is zero. The...
  13. duke37

    Step down transformers

    The output power will be less than the input power because of heating in the transformer. Efficiency may be 80% or so. Transformers can be rated in VA which is volts * amps taking into account power factor. Watts = V * A * power factor It is the current which is limits the transformer.
  14. duke37

    Suggestions for a mobile power source for a guitar amp? Car battery, etc?

    My inclination would be to dispense with the inverter and to power the amp directly from the batteries. This would save cost and increase efficiency. The amp would not need a heavy mains power supply. Golf buggy/wheelchair batteries are safer than open lead/acid car type batteries. They should...
  15. duke37

    Op-Amp Help

    This is a common circuit and is used to add several inputs such as microphones so is of great practical use. Since each input goes to virtual ground, there is no interaction between inputs and dynamic microphones do not act as speakers. The total input must be small enough to avoid clipping.
  16. duke37

    Op-Amp Help

    Where did you measure the input? The input to the total amplifier comes from a sine generator which shoud be a pure sine wave if it has zero output impedance. If you are measuring at the op-amp input, then then the voltage should be the same as the + input i.e. zero. If the voltage of the inputs...
  17. duke37

    Fan capacitors

    The $4 or $8 seems very reasonable to me. Do not use second hand components, you want reliability. Make sure the capacitors are rated fot the mains you have or for a higher voltage.
  18. duke37

    How Does One "Provide" A Different Level Of Current?

    A train signal may be controlled from a current source. If the cable is broken, there could be an indication of a fault. Just supplying a voltage does not give any indication that there is a connection. Railway slave clocks are driven with a current source to allow for long distance resistive...
  19. duke37

    Op-Amp Help

    As audioguru says in #14 the signal is almost complerely cancelled at the - input. Therefore this can be considered as a virtual earth. Current running into this position from whatever source has to be provided by the output of the amp. Thus the output current times the feedback resistor is the...
  20. duke37

    Denon Amplifier PMA 720 AE packed in

    Have you sound a schematic (circuit diagram)? Mono or stereo? The resistors may be still in this world, they are designed to get hot. The trouble could be in the output stage but if the amp is stereo and both channels are faulty, then it could be in the power supply. How far are you from Matlock?
Top