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  1. KrisBlueNZ

    Valve (tube) amplifier schematic help

    Yes, conductance is the reciprocal of resistance. The formula for conductance (G) is G = I / V (which is the reciprocal of V / I, the formula for resistance). TRANSconductance is also calculated as I / V but the current and voltage used in the calculation are not in the same circuit. In the...
  2. KrisBlueNZ

    Active low or active high signalling?

    I think the reason for the sync arrangement is flexibility. There can't be a "master" indicator because there may be only one indicator present, and not necessarily a specific one. So the requirement is for each indicator to have its own flashing logic, and to synchronise to others only if they...
  3. KrisBlueNZ

    Can I just simply replace inductor with a choke?

    With these mains filter chokes, don't you have to have equal and opposite currents flowing in the two halves? If you don't, I think the core will saturate at a pretty low current. That core must have a very high permeability to get 100 mH from what looks like only a few dozen turns of wire on...
  4. KrisBlueNZ

    Function generator sync output at twice the frequency?

    So your camera triggers on one edge (say the rising edge) of your squarewave but not on the falling edge, and you need to produce a signal that triggers the camera on BOTH edges of the squarewave? A simple way is to convert both edges into pulses of much shorter duration than the squarewave...
  5. KrisBlueNZ

    Help with time delay relay circuit

    Here's my suggestion for a 555-based design. Power from the automotive 13.8V rail and ground is applied between CN3 and CN6. R4 is a heavy duty spike suppression varistor designed for 14V operation, but its clamping voltage isn't low enough to protect the 555 so I've added a 3.3 ohm series...
  6. KrisBlueNZ

    Help with time delay relay circuit

    Availability is always a consideration, but in this case he will have to order other parts as well. In an automotive environment I would avoid CMOS if possible. Actually I'd avoid the 555 as well. Both of them have an absolute maximum supply voltage that's uncomfortably close to the working...
  7. KrisBlueNZ

    Help with time delay relay circuit

    Thanks for the extra information. What's the current rating of the float switch? Did it previously drive the relay coil directly?
  8. KrisBlueNZ

    Motor control diy

    I don't remember seeing the cord thickness specified anywhere. I was imagining it a lot thinner than 1/4". The motor shaft diameter is 3.7 mm. I guess some kind of gearing will be needed. Either built into the motor, or between the motor and the drive pulley.
  9. KrisBlueNZ

    Motor control diy

    Yes, I think it would. I suggested that motor on the basis that you would wind the cord around the motor shaft, which would give you a speed under 0.75 m/s. If you can't do that, you might be able to couple the motor drive onto a large pulley using a second large pulley next to the main pulley...
  10. KrisBlueNZ

    Technics SL220 Turntable Circuit Board Repair

    Yes. That was a lucky guess! Yes, that sounds like a good idea. See if there are any electronics hobbyist groups in your area. Someone there should be happy to do that for you for free. There are probably a lot of young students who would do it for a small fee but I don't know how you could get...
  11. KrisBlueNZ

    Help with time delay relay circuit

    You can do what you want with duke37's 4093-based design, or a design based on a 555 (not the one you've dug out - something much simpler will do), or a circuit using a couple of transistors. You would have to build it on a piece of stripboard. If you're powering it from an automotive supply...
  12. KrisBlueNZ

    Valve (tube) amplifier schematic help

    I'm talking about the power levels of the input and output SIGNALS, which are tiny in a small-signal voltage amplifier. You're using "input power" to mean the DC power consumption of the amplifier, from its B+ rail, which is a different thing. I agree it is relevant. In post #93 I listed the...
  13. KrisBlueNZ

    Technics SL220 Turntable Circuit Board Repair

    OK. The marking on the board doesn't relate to the value of the trimpots. You will need to desolder the broken trimpot and measure the resistance between the two end terminals, that is the two terminals on the same end. The value you measure will not be exactly the rated resistance of the...
  14. KrisBlueNZ

    DC to AC converter

    We need far more information. What frequency AC? What waveform? What current? The simplest thing would be just to tell us all about what you want to do. We can then make useful suggestions rather than stabbing in the dark which wastes everyone's time.
  15. KrisBlueNZ

    Valve (tube) amplifier schematic help

    I wouldn't put it like that. BTW CDRIVE's comment, while true, relates to power amplifiers, where the output power is an important factor. You are working with a small-signal voltage amplifier and the gain you're talking about is voltage gain; the amount of power in the signal (at both the...
  16. KrisBlueNZ

    Sine Tone Generation Help!

    That's a nice little project CocaCola. He used an R-2R DAC but as you said, PWM could also be used. I was favouring PWM because it's physically more compact and only needs one I/O pin, and because he probably doesn't need the waveshape to be very accurate. It's mainly the frequency that must be...
  17. KrisBlueNZ

    Technics SL220 Turntable Circuit Board Repair

    You need to determine the value of that trimpot. It may be marked with a number like "203" (that would mean 20 kilohms - a 2, a 0, then 3 more zeros, with the result in ohms). If not, remove it from the board and measure its end-to-end resistance with a multimeter. Then measure its dimensions...
  18. KrisBlueNZ

    Sine Tone Generation Help!

    I've had a re-read of your requirements. I think the only way you can do this for the price you want is to use a small microcontroller generating a sinewave using PWM. This will require some firmware development. Do you have any experience, or a friend who does? You'll also need a device...
  19. KrisBlueNZ

    ASAP HELP.. guitar preamp

    You just need an audio amplifier with an input impedance around 100 kilohms or higher, that will drive the line level audio input of your laptop. Just google guitar preamp. There are hundreds of suitable designs out there. Look for ones that are battery powered and use an op-amp. These will be...
  20. KrisBlueNZ

    Valve (tube) amplifier schematic help

    It's true that if device X produces ten times as much energy output as device Y, for the same energy input, that device X is ten times as efficient as device Y, and it's true that energy can't come from nowhere. But in amplifiers, gain does not correspond to efficiency. Gain is the RATIO OF...
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