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  1. duke37

    RF noise from a chip dc-dc step up module, fix?

    You could put the gubbins in a metal box and filter the input and output leads. The components will not be very big to filter 315MHz. You could make an oscillator and use it to drive a voltage doubler. Keeping the switch speeds down may be sufficient for the purpose but would need fair sized...
  2. duke37

    lm7805 getting really, really hot

    The 0.1μF capacitor, together with its leads forms a tuned circuit. The regulator consists of a reference and a very high gain amplifier. If the tuned circuit is at a low enough frequency where the amplifier gain is high, then instability can occur. Saying that, I have never encountered...
  3. duke37

    lm7805 getting really, really hot

    Nothing to do with your problem but the 0.1μF capacitor should be close to the regulator, not spaced away from it.
  4. duke37

    tube (valve) help

    If you go on vintage-radio.net/forum you can probably get a circuit diagram for £2 which will give the working voltages. Note that these are lethal. There is a possibility that the chassis is live, if so it should only be run through an isolating transformer. It looks as if it is a standard...
  5. duke37

    Old AC DC power supply with mechanical rectifier ?

    The relay seems to contain a magnet so that the armature will move in one direction when the input is positive and the other direction when negative. The contacts can therefore be connected in a way which will give a unidirectional output. Cunning!
  6. duke37

    Merits and Demerits of Current transformer secondary winding turns

    The number of turns affects the impedance of the transformer secondary. This should be considerably higher than the load resistance. I expect that you are using a high frequency if you have a ferrite core.
  7. duke37

    Measurement of current sensing transformer (CT)secondary winding

    Shorted turns will have little effect on the resistance if the turns are close together. Even shorts between one widing layer and the next may be hard to detect. The shorted turns will have a large effect on the inductance due to the eddy currents which are generated. I would guess that you...
  8. duke37

    Activate transistor with piezo disc

    R2 could be placed in parallel with R1 to eliminate DC bias on the piezo. I doubt if it will make much difference. A diode in the output of the 555 to charge C6 when it is positive and to allow C6 to drop gently when it is zero may give you the fade which you crave.
  9. duke37

    Not enough current to trigger relay.

    That circuit will not work and I have a stiff neck so it is difficult to see.:) Measure the current drawn by your hooter when fed direct from your power supply. I cannot draw a circuit at the present, I will try to get the equipment in the next week or so. The components you list are not...
  10. duke37

    motor driver 12v .. 2a... fail~

    Why did you fail? What did you get? You seem to have done things correctly by putting a current meter in series with one of the motor leads. Did you have the meter set to current at a range of about 5A?
  11. duke37

    motor driver 12v .. 2a... fail~

    With 2V across the 317 and at least a volt across the Darlington, you are lucky to get 9.5V.
  12. duke37

    Trouble with solder

    If everything is clean and there is a slight amount of solder on the iron, you will get the leads up to temperature quickly and then by adding solder to the joint, you will get a good joint in a short time. If you need more than a couple of seconds then either the components are not clean or...
  13. duke37

    Not enough current to trigger relay.

    You could use a 24V relay and switch it with a FET or BJT, controlled from the 12V supply. Put a catch diode across the relay to prevent high voltages ocurring. You may be able to run without a relay, if ground isolation is not needed.
  14. duke37

    PiezoElectric Tiles

    Your soldering is no better than mine.:) I suggest that you remove the solder with a solder sucker or braid and then replace with flux cored solder, using a good hot iron. Bad contacts may be reason it does not work. Lead free solder needs a higher temperature than normal 60Sn/40Pb. The...
  15. duke37

    Help making a CRT oscilloscope

    Solid bar will have a large energy loss. Transformers with iron cores are made with thin laminations to interrupt the current path. The iron needs to be magnetically soft and is usually alloyed with 4%silicon. Carbon steel is physically and magnetically hard and is not suitable. Scanning...
  16. duke37

    Activate transistor with piezo disc

    You need some input protection for the 555. The piezo can produce fierce voltages which can arc over the circuit inside or outside the semiconductors. See cdrive #37
  17. duke37

    Where would I Get My Hands On....

    A LED can have its light reduced by controlling the current. This will maintain the colour which a filament lamp will not do. It is surpising how a LED can be seen with very little current. Try a LED in series with a 1k resistor and 10k potentiometer supplied with 9V. I would be interested...
  18. duke37

    Activate transistor with piezo disc

    A fet needs much less energy to turn it on and off, however, with a 20V maximum gate potential and a source of a few kV there is likely to be a few problems. If you wish to try this, you should charge a capacitor to lengthen the pulse and put base protection in, a 10M resistor to discharge the...
  19. duke37

    Is 450 volts close enough to 550 volts for a capacitor?

    Why are you replacing the capacitors?
  20. duke37

    Activate transistor with piezo disc

    The diode should be connected to the two terminals of the piezo with the anode to ground and the cathode up so that the two diodes are chasing their tails. The current goes from ground up through the new diode, across the existing diode and down through the transistor. Just follow the arrows.:)
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