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  1. duke37

    Help with fence charger schematic

    I am not able to see the schematic at the moment but it seems to me that 15kV is excessive and much more than those fencers I have played with. What is the point of generating a lot of high voltage energy and then dissipating in a spark gap?
  2. duke37

    Series capacitor on fluorescent 125w T12 light fitting

    Most fluorescent lights use a series inductance with a value sufficient to control to the design current. A capacitor across the input may be added to correct for power factor and reduce interference. My aunt had a light with inductance and capacitance in series with the tube. The current was...
  3. duke37

    PSU advice

    A 10A fuse is way over the top. I would go for 1A. I would use an aluminium case, solidly earthed. The iEC socket will fit in easier. Make sure that the transformer is not compromised with a shorted turn.
  4. duke37

    Thyristor Help

    Your circuit ill not work. 1. The gate is held positive and the SCR will behave like a NPN trnasistor which is hard on. 2. There is no DC connection across the SCR so it cannot pass current. Normally the gate is connected to the cathode via resistor (<1k) to ensure that the SCR is not falsly...
  5. duke37

    Thyristor Help

    Show us a schematic. The peak current will depend on the coil inductance. The power loss will depend on the frequency.
  6. duke37

    I need to maintain a half-full 55-gallon drum at 180°F?

    If smaltz is gloop, then I would go for placing the drum on a hot plate and fix a contact thermostat to the outside, then the inside can be cleaned without obstruction A hot water immersion heater close to the bottom with a built in thermostat would do the job but would be difficult to clean out.
  7. duke37

    Help with Female Jack barrel replacement

    The transfomer shows a square within a square, this means it is double insulated and does not need an earth connection hence the earth pin in the plug is not wired up.
  8. duke37

    110VAC to 130VDC motor

    The motor is labelled P.M.D.C so is likely to be a permanent magnet DC motor.The only way of controlling the speed is by controlling the voltage. The speed is not given and could be very fast ot very slow. I doubt if the speed of a belt grinder is critical. Try the motor on 12V and see what...
  9. duke37

    Puzzling problem with sensor and flickering lights

    I agree with this. My sister had flickering lights in the hall, I tracked the wires with a little transmitter and a portable radio eventually finding a junction with poor connections which had been close to fire. The house is about 30 years old and was wired by an ignorant yob. He did not think...
  10. duke37

    DIY wire insulation/enamelling

    I believe that some enamelled wire has three layers of insulation. To wind a coil for high voltage, each layer should be separated by an insulating sheet. Thus the wire insulation has to withstand connection to an adjacent turn and the sheet has to withstand the voltage across several turns. You...
  11. duke37

    Help finding fault with old bass amp that blows fuses

    What do you mean 'it was way off'? by twiddling you may have introduced another fault. The voltage is there to compensate for the base drop voltage of the driver transistors, these would be about 0.7V each. The current is limited by the resistors in the emitters of the driver transistors and the...
  12. duke37

    Help finding fault with old bass amp that blows fuses

    There is an IC111 which looks at the offset output volts and only connects the speaker when this has settled. It is fed through R210 and a smoothing circuit to reduce the audio signal. Shorting the output would enable a very high current to flow before the IC111 has time to react. A transistor...
  13. duke37

    Help finding fault with old bass amp that blows fuses

    Tr122 is almost certainly all right. It has less than 2V across it and little current. It is more likely that there is a bad connection since the transistor is fixed to the heat sink which expands and contracts with temperature. You have two power lines, one positive and one negative, going to...
  14. duke37

    Help finding fault with old bass amp that blows fuses

    Is this Tr122 you are talking about? As I asked before, measure the voltage across Tr122 i.e. collector to emitter. The output transistors need about 0.6V to turn them on so there should be about 1.2V across Tr122. If this voltage rises due to a bad connection or a bad potentiometer, then the...
  15. duke37

    HELP please OTL tube headphone amp (again)

    I do not think there is a hum bucker pot in this. There are two pots on the one shaft with the centre tag of each trio connected to a grid. When you have the connection correct, the resistance from the grid to chassis should be minimal when the control is turned to the left and up to the value...
  16. duke37

    Blowing fuses on 1980's Fisher CA-880

    And make,model number and schematic.
  17. duke37

    Help finding fault with old bass amp that blows fuses

    My very limited experience has shown that if a semiconductor has failed , it has done the job properly and is dead. We have not yet seen the voltage across Tr122 which controls the output bias. As previously said, a bad connection here or a dodgy potentiometer can turn the output transistors...
  18. duke37

    Air Pump

    I would guess that, with a triac, it is a series wound (universal) motor. Measure the voltage going to the motor with an AC volt meter. A C106D is the classic sensitive gate triac and much more robust.
  19. duke37

    Help finding fault with old bass amp that blows fuses

    Edd Thank you for a readable schematic. The lamp limiter will limit the input current so will limit the secondary current. This will enable you to compare one channel with the other but may suppress the fault. I would look at the voltage across Tr122 and the connections in that area which set...
  20. duke37

    HELP please OTL tube headphone amp (again)

    Hi Edd, Most of the hum had gone when 6SN7 was removed. The HT supply was still connected so I think that the problem is not in the supply. Grounding the grids (p1 and p4) should remove any input unless it is being input via the cathode. The heaters are working OK so I do not think that a...
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