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  1. duke37

    soldering onto conductive paint or glue

    Aluminium particle will not produce a conductive paint due to the surface oxide. Conductive paint uses silver or graphite particles.
  2. duke37

    Tube amp acting very strange-- tubes acting as speakers

    Look up Wikipedia 'Audio Induction Loops'. Specification and installation details can be found in British Standard BS7594.
  3. duke37

    Tube amp acting very strange-- tubes switching on and off

    You will need to understand such circuits and to work gradually through the amp to find the problem. Since it has smoked, you may be able to see a faulty component. You are a novice and should not play with high voltages. Remember that even when the amp is turned off and unplugged, there...
  4. duke37

    What determines RPM speed of Electric motor?

    For an unloaded DC brush motor, there will be a voltage and current which will be needed at any speed. The speed will be roughly proportional to voltage and the current will depend on the torque. The torque will rise with speed due to wind resistance. Running at extreem high speeds and...
  5. duke37

    Tube amp acting very strange-- tubes acting as speakers

    Most public buildings in the UK are fitted with audio loops driven by dedicated amplifiers. All NHS hearing aids are fitted with a coil to pick up the magnetic field. This works well if installed to the proper specification although some interference can be caused by fluorescent lights. I...
  6. duke37

    Multimeter?

    I am an advocate of cheap meters so they can be blown up without too much pain. I have a couple of cheap meters with top range of 1000V, one of these went fizz at about 600V and will now only work at low voltages. I measured the input resistance which is 1M on all ranges. !000V into 1M = 1W...
  7. duke37

    Bypass circuit bmw M3

    You do not need to measure the led current, voltage measurements will do so you will not need to discaonnect anything. A led is usually fed with a resistance, the voltage 'top side' this resistance may be a better source. A fat fet will deal with the current you want or a diddy fet to drive a...
  8. duke37

    Variable power supply for supplying valve amp builds

    You could use a switched potential divider across the HT and then feed a cathode follower. If I remember rightly, a 12E1 was used for this but any power valve would do. The heater would need a separate supply because of heater/cathode insulation limits.
  9. duke37

    Help with MOSFET as a switch

    You will need a resistor from gate to source to turn off the fet when the switch is open. To switch the Vcc together, you will need a P channel fet and ground the base to turn it on.
  10. duke37

    Bypass circuit bmw M3

    I went to school too many years ago and my brain cell is discharged. I am sure that it can be done with two relays but I do not have time to work it out now. CMOS can be used to make a counter. A 4013 with Q/ to D or 4027 with J and K high will do it. A transistor to drive an output relay...
  11. duke37

    Tube amp acting very strange-- tubes acting as speakers

    All transfomers produce sound (see magnetostriction) where the core vibrates. If the laminations are loose, they will flap and the transformer can be very noisy. The higher the flux, the more the vibration.
  12. duke37

    Need help interpreting tube plate curve

    You could use two identical Hammond transformers connected in parallel but would they handle the voltage? The 4-125A will, I believe, need a stiff screen supply which will source and sink current otherwise they go bananas.
  13. duke37

    Bypass circuit bmw M3

    Take a feed from the rear light circuit so that the fog light can only be on when the rear lights are on. Use a relay which is normally off and have a switch to energise the coil. Use a contact to energise the coil so that the relay stays in when the switch is de-energised. The fog light will...
  14. duke37

    Testing High Voltage Rectifiers

    The 1.5V drop will be with 8A. I expect it will be a single diode with a drop of 0.7V at low current. My normal analog meter uses 3V for the resistor ranges, which would test a diode with 1.5V drop. It has the disadvantage that it will blow a small transistor on its lowest range.
  15. duke37

    How to reduce DC a bit without resistor or capacitor? Is there a simple solution?

    If flicker is not a problem, then C1 could be disconnected to give a lower average voltage
  16. duke37

    Quad Comparator Help

    Show us your circuit. Perhaps you have ambient noise, either electrical or light which is triggering the comparator for a short time. Some capacitors on the inputs could help as would hysteresis.
  17. duke37

    Tube amp acting very strange-- tubes acting as speakers

    That was a daft thing to do. A tube amplifier uses an output transformer which stores energy. If this is not delivered to the speaker, then it has to go elsewhere. The high voltage may arc over either outside the transformer or inside with disastrous results. An arc can be made to sing...
  18. duke37

    Testing High Voltage Rectifiers

    I looked up the data. 600V, 8A, 1.5V forward, 12ns What do you want to know, if the diode is blown, then a simple resistance measurement will do. If you want to know whether it complies with the data then sophitcated equipment will be needed.
  19. duke37

    Diode in Relay Circuit

    Saying the same thing as Harald. When the transistor is on, current passes through the coil. A diode is connected across the coil in the direction where it does not conduct. When the transistor turns off, the current will continue until the stored magnetic energy is dissipated. This energy...
  20. duke37

    Quad Comparator Help

    To drive a 150mA load, a simple fet amplifier can be used. Any medium power fet will do, I would use IRF530 because I have some.
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