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  1. audioguru2

    need help on BC337

    Yes, even a 2N3704 transistor will work. Digikey sells them for $.30US each. They sell the 2N3904 for $.16US each because they are more popular. They sell the BC337 for $.33US each. ;D
  2. audioguru2

    need help on BC337

    Hi Jpop, Just about any little NPN transistors will work in that circuit. Its supply is only 3V and  the LED driver's current is only about 25mA. I would use 2N3904 transistors. ;D
  3. audioguru2

    Beta of the BJT

    Hi Prateek, Some experts say that a transistor's base-collector junction must be forward-biased for a transistor to be fully saturated. The forward-biased junction needs extra current in addition to beta for its base-emitter junction.
  4. audioguru2

    Beta of the BJT

    Hi Shekhar, In the above transistor, beta won't be any lower than it is with a Vce of only 1V, unless the transistor is used as a saturating switch when it needs much more base current to saturate well. Design the circuit so it works with the range of beta of the transistor by using a voltage...
  5. audioguru2

    Can you put a dimmer on LEDs?

    Sure Alun, Um-Me just hooks-up his LED directly to his 12V battery with very thin connecting wires. The wires smoke a little and the LED is so blinding bright that he needs a dimmer for it! ;D ;D
  6. audioguru2

    Advice on Equivalent transistors

    Hi Guys, Most circuits use ordinary "general purpose" transistors. If a circuit spec's a BC547 transistor then you can use a 2N3904 which is almost exactly the same (except their pin-out is reversed). ;D
  7. audioguru2

    Beta of the BJT

    Hi Prateek, I am sorry but I disaggree with you. When a transistor is saturated then it takes much more than the higher-voltage beta for its saturation voltage to be low. The 2N3904 has a guaranteed minimum beta of 100 at 10mA of collector current and a Vce of 1.0V, but when guaranteeing its max...
  8. audioguru2

    Infrared Activated Switch

    Hi Indra, Welcome to our forum. ;D Philips recommend a 0.01uF to 0.1uF ceramic disc capacitor directly across the power supply pins of their NE567 and an additional 10uF electrolytic cap if the supply has poor voltage regulation like from a battery. They also say to be careful with signal...
  9. audioguru2

    Can you put a dimmer on LEDs?

    An LED is a diode with a fairly constant voltage across it, not a resistive hot piece of wire like a light bulb. LEDs operate with current, not voltage. A supply voltage higher than the LED voltage is used and the current is limited with a current limiting resistor in series with them. The lower...
  10. audioguru2

    40 mhz oscillator

    Hi Izach, You are absolutely correct, a BD241C is NPN. Motorola's datasheet is very confusing. :-[ The transistor is much too slow for 40MHz since it doesn't have any gain above 3MHz because its rise-time, storage time and fall time are much too long. :( I think the BD241C is an audio power...
  11. audioguru2

    Beta of the BJT

    Linearity of a transistor is based on a lot more than only its beta. Take a transistor with a 10k collector resistor and a 20V supply. Bias it so that the collector voltage is halfway, at 10V. Its Q-point is at 1mA. Now feed a sine-wave voltage directly to the base of the transistor until it...
  12. audioguru2

    COILED RESDISTOR?

    If it was a very long piece of wire, if it was not coiled then you might be tempted to add long connecting wires to your ohm-meter to connect to the far ends of the wire being measured. Then you would have quite an error. :(
  13. audioguru2

    Heatsink free samples

    They might give one to you if you go there dressed in a suit and have a good story about how many thousands you are going to use. ;D
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Maksar, Your parts look good and your pcb is very nicely done. ;D I guess the enormous heatsinks and high velocity fan wouldn't fit into your picture!
  15. audioguru2

    40 mhz oscillator

    A BD241C is a PNP 100V/3A power transistor. It doesn't have any gain above 3MHz. Post your circuit for us to see how it could provide 100Vp-p at 40MHz without melting. In an ordinary astable multivibrator circuit, its base-emitter junctions would try to operate well above their max rating of...
  16. audioguru2

    Amplified Ear help!!!!

    Hi DRulje, Q4 is just an ordinary amplifier. Q1's gain is controlled by its base current. With a low input sound level, R7 in series with R2 provides plenty of base current to Q1 and it has plenty of gain. Q2 amplifies the output of Q1 so that when a signal level is high enough at the output of...
  17. audioguru2

    Electronic Stethoscope

  18. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, It looks like a wicked high voltage generator. I can harly wait to see pics of huge sparks jumping all over the place! ;D
  19. audioguru2

    frequency to voltage converter

    A video signal is made of individual horizontal lines of video, followed by a horizontal sync pulse, then another line of video followed by another sync pulse etc for about 262.5 lines in North America, then the horizontal sync pulses are modified to produce a vertical sync pulse. Audio is...
  20. audioguru2

    Power Amp

    Are you talking about using a 0V reference bias voltage for the input of a capacitively coupled opamp, or biasing idle current for the power emitter followers to avoid crossover distortion? Most opamps have an absolute max supply voltage of plus and minus 18V. An OPA445AP has plus and minus 45V...
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