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  1. KrisBlueNZ

    2-10v or 4-20 dimming of 120v light bulb

    Is the bulb running from AC or DC? What voltage?
  2. KrisBlueNZ

    MOSFET H-bridge, weird effect...

    What do you mean? Are you saying that if the bottom device is a MOSFET it will conduct in both directions, but if it's an NPN, it will only conduct in one direction? AFAIK a MOSFET biased into conduction will conduct in both directions, with or without a body diode. And a saturated NPN will...
  3. KrisBlueNZ

    Transistor base resistor calculation on 2N4401

    Did you read the two resources I linked to?
  4. KrisBlueNZ

    MOSFET H-bridge, weird effect...

    Yes, that will happen, because when you drive both sides of the H-bridge to the same state, the H-bridge effectively shorts the motor out. This is called braking and it's different from simply disconnecting the power source from it, which produces the gradual slowing to a stop. If you don't...
  5. KrisBlueNZ

    Need assistance with 555 Timer Circuit

    Yes, that looks good. You haven't shown the polarity of C, or the connection from its postive side to pin 2, but apart from that, it looks right.
  6. KrisBlueNZ

    Transistor base resistor calculation on 2N4401

    Good point. If you're using it as a saturated switch, see: https://www.electronicspoint.com/resources/using-a-bipolar-transistor-to-turn-a-load-on-and-off.30/ https://www.electronicspoint.com/resources/saturation-in-transistors-bjts-why-and-how.28/
  7. KrisBlueNZ

    simple tone generator

    Simplest option: create a .WAV file with a waveform editor such as Audacity and download it onto a smartphone or an iPad. Edit: I meant iPod, not iPad!
  8. KrisBlueNZ

    Transistor base resistor calculation on 2N4401

    But the data sheet doesn't specify a minimum hFE at the collector current he wants to use. He wants to run it at 300 mA and the data sheet has hFE values for 150 mA and 500 mA but not for 300 mA. That's what he's asking. I can't give a definitive answer. I think I would use the typical...
  9. KrisBlueNZ

    Timer relay, to turn pump on, and then off

    Would it be better just to have a pushbutton to do that?
  10. KrisBlueNZ

    Sony TA-1055 repair (problems)

    Digi-Key probably have the widest range but in the UK you can try Mouser and Element 14 aka Farnell (http://uk.farnell.com). Don't bother with Maplin. I don't know of anyone else with a wide range. Element 14 / Farnell have the ON Semi MPS2907...
  11. KrisBlueNZ

    Sony TA-1055 repair (problems)

    Yes you can remove the output transistors to disable the output stage, but you'll need to remove Q207 as well, otherwise R242 will go up in smoke again. I think it's unlikely that the new TIP41A transistors are damaged. More likely something is not connected properly. According to...
  12. KrisBlueNZ

    Sony TA-1055 repair (problems)

    OK, here's the schematic of the left channel output stage with R142 circled in red. It's clear that it shouldn't be possible for any significant voltage to appear across it, because it's connected across the base-emitter junction of Q109. Either Q109 isn't connected correctly, or Q109 has...
  13. KrisBlueNZ

    Any electronics experts from South Africa?

    benjaminpetrus, This thread is on the same topic as your existing thread at https://www.electronicspoint.com/threads/555-timer.271897 which I have already replied to. Please don't start more than one thread on the same topic. I am closing this thread.
  14. KrisBlueNZ

    Timer relay, to turn pump on, and then off

    OK, here's my suggestion. The circuit is powered from 12V DC and drives a relay whose contacts can switch the 110V AC to the fan directly. The circuit is based around two ICs from the CD4000 CMOS family. U1 is a CD4093B which contains four identical "gates" called NAND gates with Schmitt...
  15. KrisBlueNZ

    555 timer

    Post a full schematic. If you don't have EDA software, draw it on paper and take a photo of it. Show all pins, all components and all off-board connections. Also upload a photo of your construction.
  16. KrisBlueNZ

    Kenwood KR-8050. A+B Speaker selection not working.

    No, that's not possible. Those components connect between the amplifier outputs and the switching, so if they failed, they would affect all speaker outputs. Here's the schematic of the speaker switching section. The G, L, G and R connections at top left are from the amplifier's speaker...
  17. KrisBlueNZ

    555 timer

    Hi there and welcome to Electronics Point :-) I don't understand your question. Pin 3 is the output. It drives something, like an LED, a speaker, a relay, etc. Pin 8 is the positive power pin, also called VCC. Pin 1 is the negative power pin, also called GND or 0V. You need to connect a power...
  18. KrisBlueNZ

    DIY Peak Volt circuit alternative

    The capacitor will charge up to the peak voltage fairly quickly, depending on the characteristics of the signal that is driving the circuit. The capacitance doesn't make a great deal of difference; it determines how quickly the capacitor will discharge between peaks, and when the input voltage...
  19. KrisBlueNZ

    Kenwood KR-8050. A+B Speaker selection not working.

    Yeah, I doubt you would find a replacement. That's why I suggested that you remove it and open it up. I think the problem will be obvious. You might or might not be able to fix it, but you should be able to get it back to its current state. Do you use all three speaker output sets? Do you want...
  20. KrisBlueNZ

    DIY Peak Volt circuit alternative

    No, 22 µF isn't much less dangerous. There's some good electrical safety advice here: http://electrical-engineering-portal.com/21-safety-rules-for-working-with-electrical-equipment Also see http://www.ccohs.ca/oshanswers/safety_haz/electrical.html
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