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  1. duke37

    ground pour under component

    There is a language problem here. Please try again. Pour means to flow a liquid or slurry. Concrete and wine are poured. Poor means insufficient. If wires comming through a printed circuit board are touching a grounded area then there will be strange effects, possibly damaging. If the...
  2. duke37

    K Type thermocouple installation

    The drilled and tapped hole will make a good thermal connection if screwed up tight. Do not use any gunge, this may not stand the temperature and if it sets will make dismantling impossible.
  3. duke37

    help-antique bell

    The 'battery' is in fact a 0.4µF capacitor. I think that the bell should be run on AC but I do not know what frequency or voltage would be used in Ulan Bator.! Edit Wikipedia 'Ringer box' says voltage 60 to 100V and frequency 20 to 30Hz.
  4. duke37

    How to make use of this

    I think CDRIVE is right but, is it not possible to check the circuit from the power input? The capacitor is essential.
  5. duke37

    capacitor and inductor

    Consider energy
  6. duke37

    Understanding a 5-transistor radio circuit

    I do not have the time to go through your calculations. However you say that Q2 is class A. This is not so. If you work from the emitter, The voltage divider will give about 0.5V, this is not enough to turn the transistor on. Thus Q2 is running in class B and is acting as a radio frequency...
  7. duke37

    how can i make my own AA battery case?

    I have made some small boxes from 3.5mm plywood which I found in a skip. I am now making a box to house a transformer from 6mm ply which came from a tobacco chest - I quite like the smell.. There are all sorts of plastic containers - what about one from the local chinese takeaway. A model shop...
  8. duke37

    Simple question, is this correct?

    I have not worked through the circuit but I do not think it right. Also no gate output should be shorted to ground.
  9. duke37

    The smallest 240vac to 12vdc power supply

    I do not think this can be done. You will want an isolated supply and there will be minimum distances specified for insulation. That is probably the reason you cannot find a very small transformer.
  10. duke37

    why we need Load resistor?

    Hi Chris, I can manage to be a lot wrong, it happens often ! In the case of a valve amplifier, the output impedance of the valve will be very high so if this is matched to the speaker, the anode voltage will vary a lot but there will be little change in current. The power output will be...
  11. duke37

    Wanted: 10uf 250v capacitor

    Make sure it is an AC capacitor, you do NOT wamt a polarised DC capacitor. That would be exciting ! Why has this been suppressed? Is it because I am not normal?
  12. duke37

    why we need Load resistor?

    I think Cdrive is a little wrong. The dynamic output impedance of a pentode could be as high as 1M but the optimum load resistance will be of the order of 10k. As Cdrive says, running a valve amplifier without a load will generate damaging voltages. Similarly running a transistor amplifier into...
  13. duke37

    Can a metal box become a resonator?

    The box will act as a screen so that hand effects will be minimised. There will be many resonances of the box, I think the lowest frequency will be due to a half wavelength in the longest dimension. You could look up Helmholtz resonator for information of acoustic resonances of a volume. You...
  14. duke37

    Understanding a 5-transistor radio circuit

    The first two transistors do not do the same thing as a ZN414, they are merlely a high input impedance amplifier. The ZN414 has a high input impedance but has automatic gain control and a detector. The ZN414 is obsolete but there is a modern equivalent.
  15. duke37

    why we need Load resistor?

    If the amplifier has an output impedanceof 0.1R, then maximum power will be obtained with a 0.1R load. It is a good way of producing smoke for a very short time. If there are reactances, then a conjugate impedance will be required.
  16. duke37

    Parallel LRC circuit analysis help

    This is partly beyond me but 4. is wrong. There is 8.49V rms across the 10R resistor. The other compnents do not come into it since they do not dissipate power. Also in 1. Ic is given as a function of Xl. I presume this is a typo.
  17. duke37

    Can a metal box become a resonator?

    A small box such as you have will have resonances in the hundredes of MHz. The effect on sub MHz circuits will be to reduce the tuned frequency due to more capacity and increase the frequency due to less inductance, the inductive effect normally predominates.
  18. duke37

    New alternator to car cause relay to buzz - can you help?

    The big threaded terminal is the battery positive and the feed to the starter. Under no cercumstances should this be connected to earth. The frame of the alternator is the earth. One of the smaller wire provides energising to get the alternator started. I assume the chattering relay is...
  19. duke37

    Forum Upgraded!

    Test: H 2 O 123 I do not get it to work, what am I doing wrong? I can get mu with Alt-230 µ, it would be nice to get omega.
  20. duke37

    LED's

    A LED will only produce light when current is passing through it. If you wish to light a LED when passing through some other part of the circuit, in order for us to help, you will need to give more information. AC, DC, amperage, voltage, rate of curent change etc.
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