Help Please with 270ns Inductor...

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unlimitedjeep
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Help Please with 270ns Inductor...

Post by unlimitedjeep » Wed Jul 16, 2003 1:32 am

Greetings all,<p>I have a RGB Interface Board out of an old Gorf aracade machine that I wish to duplicate. I am having trouble trying to find the two inductors located on the board. Here is a pic of it. The numbers on the side of the inductor read 0069-166xx-xamx. Does anyone have anyidea? I can e-mail more pics or the schematic of the board if needed. Please help!<p>Image

rshayes
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Re: Help Please with 270ns Inductor...

Post by rshayes » Wed Jul 16, 2003 5:23 am

I assume that the value of 270 ns came from a schematic diagram. An inductor would be described in nanohenries (nh). This may be a delay line rather than an inductor. The main difference is that a delay line will have a grounded metal conductor under the solenoidal winding.<p>Delay lines have two characteristics, the time delay and the characteristic impedance. I would expect a delay line like that shown in the picture to have a characteristic impedance in the 500 to 1500 ohm range. Duplicating that part will require a fair amount of experimentation, but it probably can be done.<p>Basically, you put a piece of copper tape on a plastic rod. The tape should not go all the way around the rod or you get a shorted turn. You may want a layer of plastic tape over the copper, else the wire insulation is your only dielectric and it may be unpredictable. The tape is grounded. Wind a coil over the copper tape and insulation. One end of the coil and the grounded tape are the input terminals. The other end of the coil and the grounded tape are the output terminals. If you apply a pulse to the input terminals through a resistor (about 1000 ohms) and observe the voltage across the input terminals with an oscilloscope, you will see a step, followed by a series of smaller steps. The width of the steps will be twice the delay time. If you connect a resistor across the output terminals, the waveform will change. For one value of resistance, the steps will disappear. This is the characteristic impedance.<p>You can change the characteristic impedance by changing the diameter of the form (larger increases impedance), the width of the tape (wider lowers impedance), the wire diameter (larger lowers impedance), and the insulation thickness over the copper tape (thicker raises impedance). Once you have a structure that matches the characteristic impedance, the length of the coil is changed to adjust the time delay. I would start with a 1/4 to 3/8 inch diameter form, a stip about 1/4 to 1/2 inch wide covered with one layer of plastic tape, wound with #28 or #30 wire, and 1-1/2 to 2 inches long. It will probably take 5 or 10 tries to match the characteristic impedance and another try or two to match the time delay. The coil can be wound slightly long and turns removed to adjust the time delay.

unlimitedjeep
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Re: Help Please with 270ns Inductor...

Post by unlimitedjeep » Wed Jul 16, 2003 1:26 pm

Thanks for the reply! Yes on the schmetic it says delay. There are two grounded points on each one. Do you think I can buy them from somewhere? I am pretty clueless as to what you said about duplicating one. I know someone who can decipher what you said though. Duh.....Any more info you can give is greatly appreciated. I can e-mail you the schematic also. Thanks again!

analogee
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Re: Help Please with 270ns Inductor...

Post by analogee » Wed Jul 16, 2003 7:30 pm

Is the "RGB interface" board an encoder? Might help to know the number of the 16-pin DIP IC on the board.<p>Anyway, if so, encoders (which turn RGB video into a single composite signal) need a delay line to match the luminance to the chrominance in time; the chroma filters delay the color signal so much that the black-and-white part of the signal would be too early without the delay line. The picture would show up as being smeared, with colors shifted to the right of the gray scale image.<p>It seems to me that the delay is 400 ns. So, perhaps there are two delay lines in series? I'm not sure why 270 ns would be needed. This is the mystery, from the info you've given us.<p>DigiKey sells Toko delay lines. They have a 400 ns and a 250 ns, for example:<p>DigiKey delay lines<p>As stephen says, you need to know the impedance of the delay line to use it correctly. If you look in the schematic, you will probably see a resistor in series with the input, and one loading the output to ground. Both of these should match the characteristic impedance.<p>Regards,
Todd
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Chris Smith
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Re: Help Please with 270ns Inductor...

Post by Chris Smith » Wed Jul 16, 2003 7:38 pm

Old VCRs use them.

rshayes
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Re: Help Please with 270ns Inductor...

Post by rshayes » Wed Jul 16, 2003 10:24 pm

Delay lines were a specialized part and usually custom made. There are a few made in 14 pin DIP form with multiple taps. These will be expensive and hard to find if they are still being made. What you have on your board is a pair of distributed delay lines. "Distributed" means that instead of connecting up many small sections- each containing a coil and capacitor, a single long coil is wound, and a small capacitance is formed to each individual turn. Each of the parts on your board has four connections. One of the connections on each end will be connected to ground. These connections will also connect to a thin metal sheet that goes from end to end under the winding. The other connnection on each end will have a wire going under the insulation. These are the two ends of a solenoidal coil wound over the grounded metal strip.<p>If you can get to a technical library, try to find the MIT Radiation Lab Series (28 volumes, published about 1947). Volume 17 is entitled "Components Handbook", edited by John F. Blackburn. Chapter 6 discusses delay lines. The ones you have are somewhat simpler than the ones described, but the idea is the same.<p>Most color TV sets used a delay line in the color demodulating section. This was usually a custom design built much like the ones you have, a long winding on a cardboard form with a metal strip under the winding.

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