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  1. duke37

    RED LED Darkroom light

    Ny niece is thinking of taking up balck and white photography. Low power incandescent bulbs seem to be thin on the ground so I was wondering if a light based on red leds would do the same thing as a filtered incandescent light in a darkroom. Would they affect enlarging paper? How many leds at...
  2. duke37

    Series bulbs with rectified AC

    14 months ago, I was volunteered to be the light string repairer. It took ages to find the dead bulbs or poor connections so I thought 'blow this for a lark' and I placed a 1N4007 in the plug to run the bulbs slightly cooler. This Christmas one of the strings gave a short flash and died. The...
  3. duke37

    Voltages - continuation of the discussion

    I do not understand the question. Why should there be any voltage when the DC is blocked by C1?
  4. duke37

    Rolson shake torch

    I was asked to look at a Rolson torch which should be shaken to generate energy to light a LED. I wonder if it ever worked as a shake torch. There is a bridge rectifier made from four 1N4007 diodes.This was permanently connected to two CR2032 3V lithium cells and a black cylindrical component...
  5. duke37

    Christmas tree lights

    I have just managed to get the christmas tree lights working from last christmas and now it is looming up again. The lights are small low voltage bulbs in series to get up to 230V but here the mains can be over 250V, hence the life of the bulbs can be quite short. I have placed a series diode...
  6. duke37

    DC Motor drive

    I have a very old AVO coil winder which I have fitted with a 24V DC motor. I need a variable speed and have achieved this with a Variac and 12V battery charger. This works OK but is bulky and I need my Variac for other duties. The motor takes 400mA unloaded at any speed. The current will be...
  7. duke37

    Wanted: Nuts for AVO coil winder

    A pair of traverse half nuts for an AVO coil winder required. These fit a 0.5 inch diameter 40tpi shaft with a buttress thread form. Alternatively has anyone got a suitable tap?
  8. duke37

    Low tension ignition inductor

    I am looking for details of the inductor used in the low tension ignition of cars made about 1900. This is used to create a drawn out spark when the contact is opened. I would like size, number of turns, resistance,inductance, energy storage and core type if any. There seems to be no hard data...
  9. duke37

    Pot Core dismantling

    What is the best way of taking a used pot core apart? I have tried the big hammer method, I have not managed to dismantle without detroying it. It would be nice to save the bobbin so that the number of turns can be counted.
  10. duke37

    High Voltage component

    I have repaired various electric fence units and there are some components connected in series/parallel across the output. They are light brown with a white end. I have never changed one of these even if the diodes have been blown apart. They seem to have no connection. Any idea what their...
  11. duke37

    Battery charger gismo

    My brother has given me a very unenthusiastic battery charger to look at. I have evicted the spiders and brushed out the chaff. There is no name or model, it is labelled 6 Amp and has a 6V/12V switch. It does not have an ammeter but has 6 leds. The main charging circuit has a bridge rectifier...
  12. duke37

    Polarity Protection

    Polarity Protection I was thumbing through my notebook and came across this circuit drawn about 25 years ago. I have not used it. The circuit uses a MOSFET in a reverse connection, it should need no current to drive and give a very low voltage drop. The diode I assume is the diode inherent in...
  13. duke37

    Slip ring wear

    My brother has a three phase generator which was involved in a fire. I replaced burnt out wires and a three phase rectifier. It works, glory be ! I have noticed that one slip ring is badly worn and the other is almost like new. I assume the difference is due to the different polarity. I would...
  14. duke37

    Car Water Temperature Sensor

    My friend has a 1957 Hillman Minx car which has a water temperature sensor which is a little out of calibration. TT/1200 by Smiths Industries The supply is 12V which then goes through a thermal meter, (shows maximum at zero current), then to the sensor which is screwed into the engine with...
  15. duke37

    Emitter Base Breakdown

    What happens to the collector current of an npn transistor when the permitted base emitter reverse voltage is exeeded. Using LTspice for a BC547B does not allow for junction leakage. The base voltage goes to -100V with no limit.
  16. duke37

    Log In

    I have been on the forum for two or three years without problems. Now I have to log in each time I arrive and if I start to post a reply and then go to look up some data, the first part of the post has disapeared and I have to log in again. If I do not log in, I get several advertisments...
  17. duke37

    Schmitt Oscillator

    Schmitt Oscillator I have managed to repair a Copel electric fencer even though the makers would not supply me with a diagram or information on the integrated circuit. I deduced that this is a 40106 hex Schmitt inverter. I have used previously a simple oscillator as in A in the diagram...
  18. duke37

    26 way socket

    I have been given a Protimeter Digital Grainmaster to repair. This has a socket to take a calibration card for various grains. The unit was dropped, but nobody dropped it! The calibration card has split the socket and I wish to replace it but cannot find another. It is a 26 way with concacts on...
  19. duke37

    100MHz counter

    I have a 10Mhz frequency counter board based on a ICM7216A. I would like to count to a higher frequency than this and have looked at various decade counters, they do not go to 100Mhz. CD74LS90 42MHz SN7490A 42MHz 74HCT4060 67MHZ 74HC4017 ? 77MHz Are there any decade counters that go to...
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