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  1. audioguru2

    Led display Digital Voltmeter question

    The voltmeter project still has a lot of errors. Look at the datasheet of the voltmeter IC for corrections. I think the voltmeter must be powered by a power supply that is separate from the power supply that it is measuring.
  2. audioguru2

    0-30V Stabilized Power Supply

    For 30V output, the transformer must be at least 28V. For 3A output, the transformer must be 4.2A. The power from the transformer is 28V x 4.2A= 188W. The power from your tiny little transformer is 24V x 0.435A= only 10.4W which is 14 times too small. Your transformer will power a project that...
  3. audioguru2

    slide pot?

    Most pots are 1/2W and are 100 ohms and more. You need one of these low power pots to control a power transistor that dissipates the 7W. A 7W heatsink is not very small.
  4. audioguru2

    transistor biasing

    The current gain of a 2N3904 transistor is typically 230 from a collector current of 0.1mA to about 10mA. Then with a base current of 4.3uA and a collector-emitter voltage of 5V its collector current is 1mA. If its supply is only 5V then its emitter resistor can be 470 ohms and its collector...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    R15 was used on the original circuit but is not used anymore.
  6. audioguru2

    question about symetrical swing

    A transistor needs an emitter resistor to add some negative feedback so its output is not extremely distorted and non-symmetrical, and so that transistor Vbe differences and temperature changes do not mess up its biasing. Then the emitter resistor has voltage across it which reduces the output...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    R7 is 0.47 ohms for 3A max and is 0.27 ohms for 5A max. All other resistor values do not get changed. Of course for a max of 5A you need a 28V/200VA transformer (7.14A).
  8. audioguru2

    How does this simple circuit operate?

    The Joule Thief is a very simple transformer-coupled blocking oscillator with very few parts. Almost any amount of turns on the transformer will work and a power transistor can be used (like Steven did) when the base resistor value is reduced. It is such a simple circuit (using positive...
  9. audioguru2

    varactor diodes

    22M is the highest resistor value in my collection. 200pf discharges completely (5 time-constants) by one in only 22 milli-seconds. That is not slow. You can make the discharge faster by increasing the reverse bias voltage to reduce the capacitance value.
  10. audioguru2

    varactor diodes

    A varactor diode has a very low capacitance of 2pF for ones used to tune very high frequencies to about 200pf to tune AM broadcast band radios. This is an extremely small amount of capacitance that can hold a charge because the diode is reverse-biased and therefore does not conduct but the...
  11. audioguru2

    How does this simple circuit operate?

    It is a simple transformer-coupled oscillator and voltage stepup circuit. Its output voltage is as high as the LED forward voltage which is about 3.5V for a white or blue LED. It works with a "dead" 1.5V battery that is about 1V. It keeps working until the battery voltage drops to about 0.3V...
  12. audioguru2

    Pulse transistion time

    A Schmitt trigger has an upper trigger voltage and a lower trigger voltage caused by positive feedback. Voltages from noise that are in between do not have any affect.
  13. audioguru2

    Pulse transistion time

    Use a logic inverter, gate or counter that has a Schmitt-trigger input. A CD4017 decade counter made by Texas Instruments has a clock input that has a Schmitt-trigger. Its clock rise and fall times are allowed to be unlimited.
  14. audioguru2

    LC filters

    10mV p-p is very small. If you want less ripple then increase the value of your main filter capacitor.
  15. audioguru2

    resistors

    If your 3.2 ohm device does not change its resistance when its current changes like an incandescent light bulb does then with 5.2V its current is 1.625A, not 2A. If its resistance does not change then Ohm's Law can be used to calculate a series resistor to reduce the voltage to it.
  16. audioguru2

    resistors

    Resistors are made in standard values like 0.75 ohms and 0.39 or 0.47 ohms. Yhey are made in various sizes for their power rating that you forgot to say. You can connect two or more resistors in series or in parallel to make many unusual values.
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Florian Leech, You have a very old parts list (about 5 years old) that does not match the latest schematic (about 1.5 years old) you found. The latest parts list was posted on this website somewhere hundreds of times. The zener diode and calibration trimpots do not have numbers yet. With a...
  18. audioguru2

    diodes

    You make no sense. A diode does not turn a circuit off, a switch turns a circuit off.
  19. audioguru2

    0-30V Stabilized Power Supply

    A half-decent 30V/127VA transformer is 31V with no load which produces a positive unregulated supply of 42.6V. Since your unregulated supply is very high at 48V then either your transformer is poor or your mains voltage is too high.
  20. audioguru2

    Restoring a Juliette Receiever

    Since the radio has an 8-track tape player then it is older than the internet. Finding its schematic might be impossible. They didn't have IC voltage regulators in those days. They used a 10V zener diode that fed an NPN emitter-follower. If you can trace the 9V to the emitter of an NPN...
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