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  1. autir

    Capacitors in amplifiers: polarity or not?

    I have been studying the principles of audio microphone preamps (example: http://www.ee.washington.edu/circuit_archive/circuits/micamp.html and transistor amplifiers in general. Often I see the same circuit in two different sites, in one site the capacitors are not polarised and in the other...
  2. autir

    UTP cable: diameter? Imax?

    Someone told me that each of the 8 clones of a standard cat.5 UTP cable is certified for a maximum current of 0.6 Amperes. In search of a copper wire able to withstand 1 Amp with ease (and be able to fit in a veroboard hole) I visited an electronics store. The salesman proposed that I use UTP...
  3. autir

    veroboard pen: minor cuts and failure :'(

    In need of a tool to cut the tracks of my veroboards, I have bought this pen. It accepts noses composed of many glass fibers and works as a brush. I have been unable to break a single track, with much brushing I have managed to break two or three adjacent tracks. And by that time everything in a...
  4. autir

    ElCheapo PSU

    Thank you for your reply. -> Regarding fuses: Since the transformer is 9.6 VA, the input current will be 9.6/220 = 43.6 mA. I understand that the input current will be higher than this because no device is 100% efficient, but isn't 80 mA big? In general, how do we calculate a value that is...
  5. autir

    PIC

    A PIC is a microcontroller. They are manufactured by Microchip. Just follow the links
  6. autir

    ElCheapo PSU

    Your silence implies that nobody knows where to put a fuse in a voltage regulator circuit?  ???
  7. autir

    ElCheapo PSU

    My first circuit.... isn't she a beauty?
  8. autir

    transformer measuring

    I have a transformer rated as 12Vac / 800mAh. I measured the voltage rating of the transformer with no load as Vmax=14.3 Ohm. If Rint is the internal resistor of the transformer, Rint= (14.3 - 12)/0.8 Ohm <=> Rint=2.875 Ohm. (I) When connecting an R=4.9 Ohm resistor directly to the...
  9. autir

    LM78XX & LM79XX questions

    Forgive me for raising this topic from the dead...  :-\ What is the voltage difference between the Ground pin of the LM and the ground of the power socket on my wall? What is the voltage difference between the ground output of bridge-rectified AC and the ground of the power socket on my wall...
  10. autir

    APC BACK-UPS transformer

    Six. Three on one side and three on the other. The AC voltage of the devices in my country is 220-230V, if that helps. Are the two transformers - the one from the backups 400 and the one from backups 600 - the same? How many Amperes can it support? And how do I measure it?
  11. autir

    FM WAVE PROPAGATION

    It is a matter of physics. I believe that you are looking for this? http://www.wonderquest.com/radio-waves.htm
  12. autir

    LM78XX & LM79XX questions

    I have read that electrolytic capacitors age within 3 to 30 years, depending on quality. After that they gradually dry out; their capacitance is reduced and their resistance is increased, making them useless. Can't we substitute electrolytic caps with something else if we want a long-lasting...
  13. autir

    APC BACK-UPS transformer

    Ok Mihali. I attach the service manuals. Note that they mention several transformers; Most of them are soldered directly on the PCB except this huge heavy transformer which is screwed on the metal surface of the bottom of the box. Thank you very much. apc.tar.zip
  14. autir

    FM WAVE PROPAGATION

    AM waves reflect on the ionosphere and so can travel by bouncing: ionosphere -> earth -> ionosphere etc. Higher frequencies cannot do that. So you need a line-of-sight with the other end of the link.
  15. autir

    APC BACK-UPS transformer

    Hello all I have two UPSs from APC. One is model APC Back-Ups 400 and the other is APC Back-Ups 600. Inside each box there is the PCB, the battery and a big heavy transformer. Can anyone give me details regarding what type of transformer this is? I have downloaded the service manuals but could...
  16. autir

    LM78XX & LM79XX questions

    I always thought that electronics are indestructible by time, and the only way to damage them is improper voltage. So, for example, a computer motherboard will become unusable when its electrolytic capacitors dry out? What happens when the cap dries out? Is its capacitance reduced, or its...
  17. autir

    transformer questions

    I suppose that the current rating is Irms as well?
  18. autir

    Glue vs. Silicone

    Before opening this thread I had already glued such a circuit using hot melt glue which smelled like vinegar ;D Unlucky me... I guess I have to throw the circuit away and create a new one? What other "ammunition" can a hot melt glue gun receive, besides glue and silicone?
  19. autir

    LM78XX & LM79XX questions

    I beg your pardon ?!? :o ???
  20. autir

    Glue vs. Silicone

    On several PCBs I have observed that some components are glued together. I want to do the same in a circuit of mine which will be installed outdoors: nothing but four RJ-45 female connectors soldered on a veroboard. I want to do this in order to insulate the wires from moisture and weather...
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