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  1. duke37

    Vacuum in a Can

    I don't think you can make a valve, the electrons will bump into the helium atoms.
  2. duke37

    Transmitter circuit operation explanation

    C5 is part of the oscillator tank circuit, it will have voltage across it. This is used as an input to drive T2 gate. T2 is a source follower and drives a voltage across C6 to put power into the tank circuit.
  3. duke37

    Health Care is so damn expensive...

    Many, many years ago I was head hunted for a job in Denmark but decided to stay in England because of health problems. Health care is free except for dentistry. Prescriptions are free in Wales but not England. The NHS seems to be quietly going private. I understand that MRI scanners earn a...
  4. duke37

    Transformer - Number of turns?

    Ludens gives a table of wire diameters, areas, resistances and current capability
  5. duke37

    Fm receiver circuit .

    A superregenerative receiver is quite complex. It has an oscillator which has so much feedback that it runs out of puff and stops, then when the bias subsides, it has another go. The rate of build up of oscillation depends on the input from the aerial. The bursts of oscillation must be well...
  6. duke37

    Finding a good soldering iron....

    60Sn/40Pb is very close to the eutectic. It may contain a smidgeon of other metals such as copper. What is the accuracy of your analysis? 60Pb/40Sn is the pasty plumber's solder. I use Multicore solder, not sure if it is Savbit (with copper), the label has gone.
  7. duke37

    Finding a good soldering iron....

    The op had trouble with a blob of solder on the top of a presumably cold component. If the solder is applied to a cooler part and it melts, then it should migrate towards hotter areas where the viscosity and surface tension are more suitable. Perhaps one factor is that he may be using lead free...
  8. duke37

    Is this schematic correct?

    You can check if the circuit is oscillating with a meter set to AC volts across a winding
  9. duke37

    Is this schematic correct?

    It appears that this is a tuned oscillator. To get 500V from 5V, you will need a turns ratio greater than 100.
  10. duke37

    Fm receiver circuit .

    The oscillator tank is L1, C2, C5 Energy is taken out of the circuit via C3 and is amplified and fed in by T1 collector. Is this a superregenerative receiver?
  11. duke37

    Finding a good soldering iron....

    Flux can be acid and is used for plumbing. Keep acid flux well away from electronic compoments, it will cause long term corrosion problems. I have seen transistors with no leads.:( Cleanliness is essential to get solder to run. The solder tends to run towards the heat so heat the component and...
  12. duke37

    Replacing an electrical ballast

    Get a meter. They cost less than a fish:) The line and neutral are connected the wrong way round. There is no earth connected. Neither of these would stop the thing working but is an indication of the standard of assembly. A plastic casing is quite good at holding water in.
  13. duke37

    Adjustable timer circuit

    You do not say what it is supposed to do. A quick glance finds that there is no protection diode across the relay coil. This could pop off the BC547. You should not have the circuit ground connected to the mains ground. In the UK, the mains comes in as line and neutral and there is a separate...
  14. duke37

    Resistance and Inductance

    I do not understand why polish are italian. If you have a calculator with a 1/x key, then things can be very easy, you do not need lots of intermediate calculations. I like the reverse polish calculator since I have used it for 30 years and get my numbers in a twist when using a more usual...
  15. duke37

    Trying to repair my power supply

    105 is a common temperature rating of an electrolytic capacitor. Post a picture so we can do a better estimate.
  16. duke37

    Help to Correctly Identify a Part

    If you have a general coverage receiver, then you shoud hear it on 7.2MHz
  17. duke37

    Help to Correctly Identify a Part

    The metal shiny can contains a crystal for defining a frequency - 7.2MHz. There will not be any gunge in the can, it is probably filled with dry air. Expensive ones are filled with nothing - i.e. a vacuum.
  18. duke37

    A simple way to make an oscillator+amplifier+antenna circuit for very low frequencies?

    I have old wire data so I have to convert to SI leading to possible errors. 16SWG (approx 16AWG) 0.064 inch. 7.463Ω/1000yd or 8.16E-3Ω/m To get 4Ω need 490m or 613 turns. 1V (RMS) will give 0.25A so get 153 ampere.turns. Drive it with a small audio amplifier. The inductance may be a problem...
  19. duke37

    A simple way to make an oscillator+amplifier+antenna circuit for very low frequencies?

    An inductive loop only works if you are inside the loop or very close to it. A lot of power is required to push lots of current through the loop. I would use thick wires and put enough turns on to get 4Ω or so. Using some power to drive a speaker complicates the calculations and wastes...
  20. duke37

    Resistance and Inductance

    Resistors in series, add the resistances. Resistors in parallel, add the conductances which are the inverse of the resistances. 1/A + 1/B = 1/C So 1/22k + 1/B = 1/18k so 1/B = 1/18k - 1/22k Using a reverse polish calculator and using ks. 18 1/x 22 1/x - 1/x gives 99 so put 100k resistor in...
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