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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

    My first circuit.... isn't she a beauty?
  5. 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...
  6. 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...
  7. 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...
  8. autir

    transformer questions

    1) What measurements can we make in an AC/AC transformer with nothing but a digital multimeter (and diodes, capacitors, resistances etc.)? 2) Suppose we have an AC/AC transformer rated 12V/800mA. Do the values refer to rms, peak or p-p? 3) After rectifying the AC with a bridge and connecting the...
  9. autir

    TV cable connections

    In order to give signal to two different cables, the TV technician stripped the cable coming out of my TV antenna and the two other cables. He then twisted all three cores together and all three nets/foils together. He insulated the junction with tape. This cabling is on my roof and has no...
  10. autir

    BNC connectors in 50 and 75 Ohm cables

    I have removed the TV socket in my wall and installed a BNC connector in the end of the cable. It is a typical 75-Ohm cable. The BNC connector was bought for usage with RG58 50-Ohm cables. Will I experience problems?
  11. autir

    LM78XX & LM79XX questions

    It is mentioned in the datasheet of the LM78XX series that for the standard operation the pins 1 (input) and 2 (ground) must be connected using a capacitor of 0.33
  12. autir

    Voltage regulator + current amplifier?

    I have read that voltage regulators dispose of surplus power by dissipating it as heat. I have an idea, most probably something is wrong but I would like to ask you. What if the regulator supplied just a small amount (~10mA) of current to a current amplifier which would provide the "real"...
  13. autir

    Maximum current for AC/DC adaptors

    (Why was the previous topic locked, gentlemen? ???) From what I have read I have realised that the current listed on most unregulated AC/DC adaptors is the one needed for output voltage to take its nominal value. How can I determine the maximum current rating for an adaptor (without destroying...
  14. autir

    Simulation in Linux?

    For the past few hours I have been trying to install gEDA. Does anyone know of a good scematic design & simulation program in Linux? I know some titles but I do not know which is good and which is not. I am mainly interested in small circuits and simple, analog electronics.
  15. autir

    Digital multimeter powered by adaptor?

    I own two cheapo (~10 Euro each) digital multimeters, and have been paying fortunes for 9V batteries. Can I supply the multimeters with power coming from a DC PSU or an adaptor/transformer? What are the cons of this? possible problems?
  16. autir

    AC/DC adaptors: voltage over normal?

    Over the years I have collected several AC/DC transformers/adaptors. These adaptors provide higher voltage than their nominal value. Below follow some calculations I have made with one of them. The theoretical voltage of the adaptor is 3V DC. I connected several resistances in the adaptor's jack...
  17. autir

    New member says hi!

    Hello to all. Since I am new to this forum, I thought it would be good to introduce myself. I am a pre-graduate student at the department of informatics and telecommunications of the university of Athens (yes, I am Greek :)). Until recently I had been the type of person who likes electronics...
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