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  1. duke37

    Does anyone know of a modern capacitor with these values

    Thats a powerful beast you have there ! 20MMF is an old way of expessing 20µµF or 20pF in todays money. It may be difficult to get a 20pF capacitor so you could use two 10pF capacitors in parallel or use a 22pF capacitor. I do not think the value is critical. The voltage rating may be...
  2. duke37

    Measuring Current From AC/DC Adapter

    Your power supply seems to be 88% efficient. You measure the input power, multiply by 0.88 to get output power. W = V*I so I = W/12 Putting it all together, I = inputP*0.88/12 or I = inputP*0.073 Alternatively, the ratio of the currents is 4.4, so multiply the input current by 4.4. Try...
  3. duke37

    Measuring Current From AC/DC Adapter

    It looks promising. You are providing 18W and consuming 20.5W so the PSU is quite efficient. I would do the comparison using power rather than current because of the complication of the power factor.
  4. duke37

    Amplitude and Frequency

    I use a blue coat as a background for taking pictures. Have you managed to get a glass to ring with a wet finger? I have never used Audacity but a review I saw says the autocorrelation function is good to determine the note. I see that some USB oscilloscopes have this function and software...
  5. duke37

    Over heating transformer HELP!!

    You will need to find 1. What voltage the camera requires. 2. What current each camera requires. 3. Whether they need AC or DC. 4. If they need DC you will need a power supply not a transformer. 5. Is your 'transformer' really a power supply?
  6. duke37

    delay circuit

    Two comments 1. The input is AC coupled so interference could give false triggering. 2. You could use a FET instead of the relay. A diode across the solenoid can eliminate high voltage high current transients.
  7. duke37

    Desoldering

    No electronics solder has more lead than tin. High lead solder was used by plumbers where pipe joints were wiped. This solder had quite a wide pasty phase. There is much confusion here since both electronic solder and plumbers solder are 60/40, just the opposite way round. 60% tin 40% lead is...
  8. duke37

    shaft rotation detector

    I have had a look at the availability of Hall effect devices, the A3144 is common and cheap. The Hall effect device will go in as a direct substitute to the reed switch but would need a 12V supply. It will be easier to fit than the delicate reed switch. When we fitted up our ten inch shaft...
  9. duke37

    100v supply for UK usage?

    You can keep the amp at low voltage with its normal input lead and use an external tronsformer, an 80V transformer will give compensation for a change from 60Hz to 50Hz. If you make internal modifications, then you will need to fit a standard UK lead. Are there two primary windings? Check...
  10. duke37

    Amplitude and Frequency

    Your pictures do not help. Draw the circuit (schematic) with chip type and component values and scan or photograph it. You should measure the frequency of the glass resonance by energising the rim with a damp finger. Use a microphone to get it into the computer and use a program to measure...
  11. duke37

    shaft rotation detector

    It is rare that anyone can beat Steve to the draw ! I have used a reed switch on a 10 inch shaft up to 1000rpm. It worked for two years. I attach a simple circuit using a 4093 quad two input Schmitt NAND, one gate is not used and the spare inputs should be earthed. Steve will have guessed...
  12. duke37

    shaft rotation detector

    It is rare that anyone can beat Steve to the draw ! I have used a reed switch on a 10 inch shaft up to 1000rpm. It worked for two years. I attach a simple circuit using a 4093 quad two input Schmitt trigger, one gate is not used and the spare inputs should be earthed. Steve will have...
  13. duke37

    Measuring High Input Voltages

    Please give more information on what you want to do. Almost any multimeter will be able to measure voltage up to 100V.
  14. duke37

    I need to fix a sub amp

    What is a plate amplifier? Give details of make, model and active devices with a circuit diagram if possible. What bad wiring do you have/ What is overheating?
  15. duke37

    shaft rotation detector

    Combine harvesters used a magnet on the shaft which closed a reed relay. Newer systems which I do not know about would use a Hall effect detector. It all depends on the size of the shaft, the speed, the space available and the balance required. The output would be a square wave, a voltage...
  16. duke37

    Should be simple to answer.

    The instructions clearly state that the correct voltage is listed on the label. It is very doubtful if the unit will operate on a significantly lower voltage. There is a mechanical switch (relay?) inside which will need power to operate.
  17. duke37

    sl100 and sl100b transistors

    According to the data, the NTE108 is a delicate very high frequency transistor which will pass only a low current, not what is wanted here. NTE108 15V 50mA Edit The SL100 is 50V 0.5A, nothing like the NTE108 There are many FETs which could also be used.
  18. duke37

    sl100 and sl100b transistors

    Almost any transistor will do that can pass the load current. BFX84 60V 1A BFY51 60V? 1A 2N2222 30V 0.8A ZTX653 100V 2A The SL100 and SL100B are not listed in my book. Why are circuits listed using rare components?
  19. duke37

    Variac

    There is about 1V between the turns on the Variac and so if two turns are connected together, a very large current will flow. Going across more than one turn will make the matter much worse. The small brush is only wide enough to be able to step from one turn to the next and has a significant...
  20. duke37

    Buck converter getting started ?

    MC34063 As I read the data, the 0.22 resistor is there to limit the current when the voltage drop is 300mV. I do not know whether this would affect the frequency or just add a delay.
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