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  1. duke37

    a small doubt

    Note that this circuit produces a considerable reverse voltage on the base/emitter of the transistors. This was OK on the early pnp junction transistors but the newer epitaxial transistors should be limited to about 7V. At 9V you may be damaging them. A couple of diodes could be added to...
  2. duke37

    Old Electronics Parts & Diagrams

    If the top 'transformer' is in fact a choke, it will have two leads only. I do not like the look of the black blob on it, check to see if there is a connection through it. You will need to disconnect one wire to do this. I see no problem with heat and soldering, the lugs are far away from...
  3. duke37

    Triangular signal shift phase

    Bon jour belhouss13. I presume you want a triangular signal with a frequency of 3.6kHz locked to another signal. Note K is degrees Kelvin. Upper and lower case letters are critical in electronics. You say you have triangular signal already, please tell us how this is produced. If you wish to...
  4. duke37

    tuned (tank) circuit, oscillator, Q

    There is a difference between unloaded and loaded Q. A valve transmitter pi match circuit could have a loaded Q of 12 but the coil and hence the circuit should have an unloaded Q of over 100 to keep losses down. No tuned circuit worthy of the name will have a Q of 2. At any frequency there...
  5. duke37

    garage door opener

    The capacitor is a start only capacitor so will likely go pop if used for an extended period of time. Normally start capacitors are disconnected as soon as the motor is up to speed but here it perhaps could be left connected if the running time is short. The smallest grain grinder that I have...
  6. duke37

    tuned (tank) circuit, oscillator, Q

    The energy will be the same in the capacitor and inductor, the energy passes from one to the other twice per cycle at the resonant frequency. Your example of a large capacitor and small inductor will not work as you expect, the capacitor will have sufficient inductance to affect the frequency...
  7. duke37

    Circuit trigger on specific preset sound

    An FM radio will produce a loud hiss when no signal is received. The muting is turned off to when this hiss dissapears. Radio amateur repeaters use a tone which is below the audio range to activate them. Different repeaters use different tones so that access can be selective.
  8. duke37

    Recharging water batteries

    Copper can be plated from an aqueous soltion but aluminium needs a very high temperature for production. Your cell looks to be not rechargable.
  9. duke37

    Making a battery

    You will need several cells to get 12V. You could look up a book written by my brother-in-law for the voltages available. See Gibson and Sudworth. Battery research has taken place over many decades and there seems to be no satisfactory solution. The lead/acid battery is most common, any battery...
  10. duke37

    Circuit trigger on specific preset sound

    You will need to define the type of sound that you wish to use. This could be frequency, amplitude, harmonics etc. It appears that you are using amplitude only, this is the easiest to do. Analysing complex sound can take a lot of calculations. Look up fast fourier analysis.
  11. duke37

    diode for super low voltage?

    A FET can produce a very low resistance with no offset voltage, you would need one for each wire and a driving transistor to get the phase right. Presumably 12V is available.
  12. duke37

    Record player motor voltages

    Soldier joints need saluting.:) Sticky tape is not the way to go for any decent electrical circuit. Short the amplifier input and see if the hum disappears. If so, short the two terminals at the pick-up head and see if it disappears, if not, the fault is possibly a bad connection in the cable.
  13. duke37

    eMOSFET and common emitter amplifier

    Not quite, in #3 I suggested that he should look at the DC conditions, he did not do so and Colin has done this for him. Get the DC conditions correct to start and then add AC variations.
  14. duke37

    SIMPLE FUSE QUESTION

    In the UK two fuses must not be used as reasoned by Harald. I do not know the regulations in Outer Mongolia.
  15. duke37

    help with a basic 5 LED circuit

    A 555 is not my thing but here it can be used to flash leds alternativly. Make it run as a flip/flop and place your reds between output and ground and your yellows between positive and output. The 555 can supply sufficient output without amplification.
  16. duke37

    Rotating motor direction

    I have mains driven synchronous clock which has evil intentions. If the power goes off, it almost always starts in reverse so I leave it to run for a few minutes before trying again. I have to get the washing machine out to get at the switch, I think it is laughing at me.:p
  17. duke37

    eMOSFET and common emitter amplifier

    The gain in your npn circuit could be limited by the collector voltage. Have you worked out the DC conditions and the maximum output voltage swing that you can get?
  18. duke37

    two transistor voltage regulator

    20V-0.7-0.7 looks right to me. The collecctor current of T1 will be similar to the emitter current which can be calculated from the voltage and the load resistance.
  19. duke37

    Sansui SP-2500 Speaker Crossover Repair

    Capacitors have two plates or foils separated by an insulating layer, maybe air, plastic or aluminium oxide. To get reasonably large capacitance in a small component, the gap contains an electrolyte and when a voltage is applied, a very thin insulating layer is generated so giving a high...
  20. duke37

    Record player motor voltages

    As advised, run it direct from a mains plug. The voltage is high and will bite so be careful to insulate everything properly. The original wiring probably put its supply through a switch which controlled both the amplifier and the motor. You may want to do this when you fit your new amplifier.
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