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  1. duke37

    Op Amp - what am I missing

    I have looked at an op-amp with gain-bandwidth product of 3MHz and gain of 200k. Inverting, input 2k2, FB 39k, using 5spice. The frequency response seems to be adequate.
  2. duke37

    Op Amp - what am I missing

    The inverting op-amp has the - terminal at virtual earth. The reason you are seeing anything here is that the amplifier is clipping so not providing feedback. You should have a dual supply to get it to work properly. The amplifier has to work less hard if you use it as a follower with gain...
  3. duke37

    How do I run a 24VAC solenoid off of a couple of 9V's?

    There is NO AC component when running on DC. When running on AC, the current alternates in direction and induces currents in any conducting material nearby by transformer action. Pole pieces are normally laminated to reduce this effect.
  4. duke37

    PCB designer

    Please read #5 and #6.
  5. duke37

    How do I run a 24VAC solenoid off of a couple of 9V's?

    Try it on a 12V battery such as in a car. 36 ohms will take 333mA. Dissipation will be 4W which should not overheat the solenoid since there is no AC component. If it works, get a 12V lead/acid rechargable battery.
  6. duke37

    Momentary Knob?

    What about a wheel out of a computer mouse? It will doubtless need som extra circuitry.
  7. duke37

    How do I run a 24VAC solenoid off of a couple of 9V's?

    Inrush current 0.41A. Assume in a worst case that this will apply to DC also, you will need a fair sized battery for this. Holding current 0.28A. The holding current will be less when the solenoid is pulled in because the inductance is increased. The DC current will not decrease when the...
  8. duke37

    AC generator design problems

    Find an old transformer with E and I laminations. Dismantle and rebuild with just the E laminations passed in from one side and try that. Pass the magnet over the cetre leg.The spool will give the output.
  9. duke37

    AC generator design problems

    The core needs to be laminated as said. Look at an old, broken heavy wall wart and look at the transformer laminations. A good alternator design is used for car generators. Get a faulty one from a scrap yard and see how it is constructed and how the poles are laminated. You might need a big...
  10. duke37

    why common emitter configuration is most widely used as an amplifier

    Because it can amplify voltage and has the highest power gain.
  11. duke37

    How do I run a 24VAC solenoid off of a couple of 9V's?

    To measure resistance you need a meter which will measure resistance. There are many cheap digital meters which will measure volts, AC and DC, current and resistance. Did you have the batteries in series or parallel? If the batteries are in series you should measure 27V. Check that this does...
  12. duke37

    How do I run a 24VAC solenoid off of a couple of 9V's?

    I could not find any current specifications on the website. A simple solenoid will work on DC better than AC so you will need a lower voltage/current. The AC current is determined by the resistance and inductance. The DC current is deternined by the resistance only. Measure the resistance...
  13. duke37

    multiple displays

    Looking at Wikipedia I found this. "Several passive indicator devices may be connected in series, but a loop must have only one transmitter device and only one power source (active device)."
  14. duke37

    Amplifier antenna question

    As I said "The difficulty is keeping this rubbish out of sensitive equipment." If you have a weak signal, then a better antenna can help. An amplifier at the antenna to raise the signal level before the co-ax cable can minimise the degradation of the signal/noise ratio. Most TVs these...
  15. duke37

    Amplifier antenna question

    If your terrestrial signal is low, you will need a tall mast with the antenna high up to clear surrounding obstacles and a very sensitive amplifier at the antenna. Even then, the signal may not be good enough. Why not use a satellite?
  16. duke37

    Heathkit O-11 Oscilloscope Repair

    I see the O-11 is AC coupled only. This is a distinct disadvantage, it does not allow you to see how audio circuits are clipping which will occur if DC biassing is wrong.
  17. duke37

    Going shopping

    If you are tuning a radio and looking for a maximum, then an analog meter is much better than flickering digits. I forgot to add a big hammer for when you get frustrated!
  18. duke37

    Going shopping

    Long nosed pliers Side cutters Solder sucker Desoldering braid Heat shrink sleeving A bunch of leads with a croc clip at each end Analog multimeter Digital multimeter My opinion on the meters is to buy cheap and then when you blow them up, as you may well do, buy some good ones. I...
  19. duke37

    Last night...

    Was it Elvis Presley?
  20. duke37

    do i need resistor for 50-70 leds?

    If you connect all the leds in parallel as you suggest, you will use three times the current that three leds (and resistor) in a string will use. To make string, connect the + of one led to the - of another. Repeat and add a resistor, calculated to give 10 to 20mA. The current now goes through...
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