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  1. duke37

    Frequency Response of split core current transformer

    They use a ferrite core so should work at high frequencies.
  2. duke37

    I need help building a solenoid controled by a rheostat

    As an alternative to a spring in Alec's suggestion you could use a bar magnet. They would not need a power source. Some experimentation to find the best or simpest solution would be needed. Edit: and be friction free
  3. duke37

    I need help building a solenoid controled by a rheostat

    Relays are thirsty beasts and get hot. They are designed with the minimum gap to do the job to keep the dissipation as low as possible. In your case you want a considerable force over a fair distance. A solenoid does not concentrate the magnetic force, it just sprays out the end. A better...
  4. duke37

    Wire One switch to multiple batteries?

    Why not use a common negative supply and one switch to turn on the Arduino. This supply would be also be used to turn on a fet or other transistor for each channel.
  5. duke37

    I need help building a solenoid controled by a rheostat

    So, you are opening the magnet gap when the key is pressed. The key will go down easier as the key is pressed due to the attraction getting less as the gap gets larger. This is different fom the organs I have played where the key becomes harder as the ranks are added. If you wish to use an...
  6. duke37

    Replacement Capacitor

    Is it part of the speed control or is it an interference suppressor? A normal capacitor in a speed control circuit would only have two leads. A picture would help.
  7. duke37

    How to calculate R and C for Am Demodulation envelope detection?

    Your circuit looks very strange, shouldn't the ground terminal of the scope be connected to ground. I would not know how to calculate the values but R needs to discharge C fast enough to follow the wave form. The DC offset will affect the discharge rate and may allow 100% modulation to be...
  8. duke37

    Radiogram, no sound

    Adam A rose by any other name would smell as sweet.;) I have been called an old fart!;) Trevor
  9. duke37

    I need help building a solenoid controled by a rheostat

    I do not think that you need a solenoid. You could fix a bar magnet to the underside of each key and a long U shaped electromagnet the length of the keyboard to repel the key magnet. A long solenoid will have a strong magnetic field at each end and very little in the middle. Repulsion rather...
  10. duke37

    Radiogram, no sound

    I think I may have been renamed Bob. Valves are not much different from fets but they bite much better. I have not checked the voltages with the published values but they look right. The EL84 is a power valve and does get hot but if the capacitor feeding the grid is leaky, then the valve will...
  11. duke37

    Audio transformer for crystal set help

    Chris said "What Duke says here (he's an old fart) is quite true." There is one old fart here and lots of new ones.:p The diode in the supply is to protect the circuit from reverse polarity.
  12. duke37

    Weird Meter Problem!

    With a high input impedance meter, a broken input lead can give all sorts of funny readings. Measure something you know to check.
  13. duke37

    Radiogram, no sound

    When you say it comes up with nothing, do you mean that there was zero resistance or no connection? As previously said (thanks Edd), if there is hum, it is most likely that there is high tension, over 200V. Yet you are talking about mV. Perhaps you have blown your meter possibly by measuring...
  14. duke37

    Audio transformer for crystal set help

    Early transistorised radios used transformers and you could take the transformers out of these or use the audio amplifier complete. Later radios used transformerless circuits.
  15. duke37

    Project: Charging devices with Eolic Energy

    I do not rhink you are on a winner here. There is very little energy in the wind unless it is gale force. To get a reasonable anount of energy out, everything must be optimised. Fan The fan you have produces a large velocity of wind. To get it to spin at 2800rpm, you will probably need 300CPM...
  16. duke37

    Radiogram, no sound

    Unplug the radio. It looks as if your transformer is dead, Measure the resistance at the mains plug, You might get a resistance of about 100Ω. Measure the resistance between P1 of EZ80 and chassis, also between P7 and chassis. A couple of hundred ohms would be expected. I cannot understand the...
  17. duke37

    Radiogram, no sound

    The voltages you measure are absurd and I think you should get help for your own safety. 1. Take out the EL84 to protect it. 2. EZ80 Measure the AC voltage between P1 and chassis and P7 and chassis. Both of these should be about 225V AC. 3. Measure the DC voltage between P3 and chassis, it...
  18. duke37

    Can anyone identify this item please?

    I have no information on the thermocouple. You could go to the maker, go to a caravan maker, go to ebay or go to Screwfix. The problem is getting one to fit. They are made with mineral isulation (magnesia?) between the inner and output. This is sensitive to moisture so the seal must not be...
  19. duke37

    Is it possible to power relay and relay circuit with same battery?

    I would use an ordinary diode for D1 (1N400*).
  20. duke37

    Can anyone identify this item please?

    That is a thermocouple, the two connections are the outer sheath and the inner wire. They can go open circuit or short across in a cool section. I do not have such a burner but know of two persons who keep a spare thermocouple. You are unlikely to get 1.9Mv but the sparks would light the...
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