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  1. audioguru2

    Soldering: what am I doing wrong?

    I use a Weller temperature-controlled (700 degrees F) soldering iron, rosin-cored solder and wipe the tip on a damp sponge just before each joint . The soldering is perfect and the tip stays tinned and lasts nearly forever.
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    That's great! ;D Did you use the original little 2N2219 transistor as Q2? Doesn't it get too hot when the project's output current is high and its voltage is set low? Did you use the original 24V transformer? Does the project give more than about 25VDC at 3A without ripple?
  3. audioguru2

    Service Manuals database

    The website with the manuals doesn't work. I'll try again later.
  4. audioguru2

    Electromagnetic field interference.

    If the grounds aren't connected together then the ground wires will also need shielding, in addition to the signal and power wires' shielded wiring.
  5. audioguru2

    Facing problem in inverter Design

    If you have a 12V battery then the transformer must be 12V-0V-12V which is also called "24V center-tapped". A 5A transformer will drive a 55W load with your PWM sine-wave.
  6. audioguru2

    Plz help me in understanding this RF reciever

    The capacitors in the opamp circuit are filters. The larger capacitor following the 100k resistor smooths the output of the receiving transistor to DC. The 1nF capacitor has a small value and smooths the 433MHz but allows the signal's modulation to pass to the opamp. Look up Super-regenerative...
  7. audioguru2

    Electromagnetic field interference.

    The two batteries must have their ground wires connected together, and the shields for the wires must connect there.
  8. audioguru2

    Simple help with transistors!!

    Actually, your transistors are connected as emitter-followers and don't need a base resistor. If the emitter is grounded and the load is between the collector and positive supply then the base would need a series resistor to limit its current. With a 12V supply, a 1 ohm resistor would limit the...
  9. audioguru2

    Simple help with transistors!!

    Hi Um...Me, Q1 doesn't have a base current-limiting resistor so it will fry. Q1 is not needed. The LED also doesn't have a current-limiting resistor so it will also fry. The relay coil makes a very high voltage when it is turned off because it is an inductor. The high voltage will destroy Q2...
  10. audioguru2

    Service Manuals database

    Do we dare to go there now? I am looking for the service manual for a JVC 5-channel receiver model RX-7030VBK that was dropped and a circuit board has a broken-off corner. The thing was thrown away and doesn't work.
  11. audioguru2

    BJT biasing formulas

    Hi Walid, Your calculations are correct and you have a transistor stage with a voltage gain of 10 and it has very low distortion. ;D
  12. audioguru2

    Aaaargh! 555 circuit works well with LEDs but not with relays...

    Use a relay that has two sets of contacts. Or use the single transistor driving two relays.
  13. audioguru2

    Want to power up my programmer

    Hi Shaiq, The LM317 needs a minimum input voltage of 3V more than its output to regulate properly. So the circuit needs a minimum input voltage of 16.5V. Two 9V batteries have a voltage that drops to 6V each as they run down which is too low for the LM317. Rechargable 9V batteries are only 7.2V...
  14. audioguru2

    Plz help me in understanding this RF reciever

    The opamp circuit doesn't make sense as you drew it. If the opamp's inputs are reversed like I draw it, then it would be a Schmitt Trigger and would have a square-wave output.
  15. audioguru2

    Aaaargh! 555 circuit works well with LEDs but not with relays...

  16. audioguru2

    pnp vs npn?

    A circuit that uses NPN transistors has a positive supply voltage and the negative of the supply is common or grounded. A circuit that uses PNP transistors has a negative supply voltage and the positive of the supply is common or grounded.
  17. audioguru2

    Aaaargh! 555 circuit works well with LEDs but not with relays...

    Your relay uses a lot of current for a little 9V battery to supply, so its voltage quickly drops to below the voltage required from a 555 to operate the relay. The battery will last longer when a transistor is used to drive the relay. I would use a 2N3904 or a BC547 transistor and a 1N4148...
  18. audioguru2

    Aaaargh! 555 circuit works well with LEDs but not with relays...

    Connect a resistor between the output of the 555 and the base of the transistor to limit the current. Use about 1k ohms. The current ratings of the diode and the transistor should be the same as the relay coil's current. We can't recommend which diode or transistor because you don't tell us the...
  19. audioguru2

    Has anybody heard from Staigen?

    Yea! Staigen is OK! ;D ;D I hope he gets his pc fixed soon. We were worried about him.
  20. audioguru2

    transistor

    A transistor with a 300mA collector current and a 40mA base current has a current gain of only 7.5. This is an extremely low gain number for a low power transistor. I would use a 2N4401 NPN transistor for a 300mA collector current. Its base current will be somewhere between 1.5mA and 6mA.
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