Search results

Search Forums New Posts
  1. duke37

    current flow

    This is not an inverting op-amp, it is a comparator with a massive dead band. For an op-amp to work linearly, the feedback must be to the - input. If you turn the op-amp upside down, then you will get an inverting amp with a virtual ground at the - terminal. 5V in through 10k = 500uA...
  2. duke37

    Gilbert Cell

    You have no bias on the inputs. You have the inputs shorted so there is no signal in. You have no power supply for the output. You have shorted the output signal. I am surprised that you got any output signal. I attach a sketch on how the cell should be fed and how the signal should be...
  3. duke37

    overheating of the variable resistors

    Show a circuit diagram. If the resistors burt out, they onerheated ! What are you trying to do?
  4. duke37

    Gilbert Cell

    The only component that you want for a simulation is the current source. You can use a resistor for this giving about 1mA. The LO signal should be about 100mV +/- from the mean in order to turn the transistors fully on and off. This is often done with a centre tapped transformer with the...
  5. duke37

    Gilbert Cell

    Who is NI? Can he help? The current source goes to ground. The RF input will need a positive bias (2V?) and a balanced signal. The LO will need to be 2V more positive and balanced. The output needs to be at higher voltage still and will have a balanced output. The frequencies do not...
  6. duke37

    Gilbert Cell

    The diagram shows which are the inputs and output. LO is local oscillator. RF is radio frequency. IF output will contain LO-RF (or RF-LO) and LO+RF. If the cell is well balanced, the output will not contain LO or RF.
  7. duke37

    Having negative reading with 2 DMMs !!

    The roundabout looks like a gold plated switch pattern and will be mated with a dozen wipers. You have put blobs of solder on this - bad news.
  8. duke37

    Identifying 3 unkown components

    Second set are electrolytic capacitors 100uF 25V, but why uM? The negative end has a black belt ! The third set could be wire wound ceramic high temperature resistors or plastic capacitors.
  9. duke37

    Help with transformer. Large surge currents

    This can be very difficult. A low voltage transformer out of a radio may well have a primary with several taps for different mains voltages. Check how many windings you have with an analogue meter. The secondary, possibly low voltage, would have thick wire. Putting the mains on a low voltage...
  10. duke37

    Someone help me with LEDS!!!

    I see no easy way with that switch, I will have to think about it. With a two pole four way switch it would be easy.
  11. duke37

    Help identifying valves

    I have no idea where your recycling centres are. Common valves are not worth much. TV valves are ten a penny except PL509 which can be used for high power audio or RF amplifiers. I understand UL42s are getting rare and B9A double triodes are used by audio amplifier builders. My brother found...
  12. duke37

    Help identifying valves

    Some old triode valves are worth a lot of money, also big transmitter/audio valves. Sort the valves by their bases and whether they are glass or metal. If the type number is not clear, do not scrub the valve to clean it. The number will disappear forever. Valve testing is only an...
  13. duke37

    Using 2 power supplys charging 1 battery

    I wouldn't, if it is a lead acid battery you will need 14V and the 12V supply will not be of much use if it is in fact 12V. If the supplies are different one may be doing all the work. I would even be hesitant about using two similar ones.
  14. duke37

    current flow

    The three circuits A B and C are identical. The 'top' battery passes current through the 'top' resistance and the 'bottom' battery passes current through the 'bottom' resistance. When you add R3, this makes the two loops interact and some calculation is required.
  15. duke37

    PopularAltering a LED Flasher Circuit? - Will it support MANY LEDs???

    A CMOS 4093 contains four gates, one can be used as an oscillator with similar values of R and C as the 555 circuit. A spare gate can be used as in inverter so that one set of leds can be turned on when another set goes off (Two fets required). Alternatively you could have four oscillators...
  16. duke37

    Wall Wart has a hissing sound and crapped out

    Woody. Steve is excellent and I like his humour but I think you are very hard on the rest of us. I try to answer simple questions within my limited knowledge. There are several other very good contributors but we sometimes get an odd ball who tends to get weeded out. The power supply you...
  17. duke37

    Arduino uno board crystal

    A crystal has a series resonance frequency and a parallel resonance frequency. These are very close together. I would think that either crystal will work but the frequency may not be spot on 16 MHz. You will not be able to find a 16 mHz crystal !! :) :)
  18. duke37

    Powering a power supply

    You are dealing with dangerous voltages and need proper insulation. Get a box fitted with DIN rails to mount the power supply. Connect to a flexible lead as previously advised. Use a grommet and cable clamp. eKretz has suggested that the ends of the cable should be tinned. I used to do...
  19. duke37

    PopularAltering a LED Flasher Circuit? - Will it support MANY LEDs???

    Your oscillator circuit does not give a really sharp tun on/off signal and the better circuit in your reference uses a 555 chip. This can provide enough current to drive a few leds directly. If you want to use a lot of leds, then a separate switch is required which will take the current. A...
  20. duke37

    PopularAltering a LED Flasher Circuit? - Will it support MANY LEDs???

    That circuit is a bit dubious, at 9V it could bias the transistors negatively more than they are can deal with. A diode in the emitter lead will stop reverse current. You could then increase the voltage supply to 12V which is nice to drive some fets. Just connect the fet gate to the collector...
Top