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    VTA-70 LED wiring....

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    4MarkNY

    Posts : 19
    Join date : 2009-10-13

    VTA-70 LED wiring....

    Post by 4MarkNY on Thu Mar 15, 2012 11:02 am

    I'm kind of pimping this one up a bit, being my second build (been collecting parts for 2 years, high time, no?). The chassis was too oxidized to clean up nicely, so it was off to my buddies plating shop,that normally does bumpers for collector show cars.I opted for the nickle chrome finish.
    Anyway, the driver board is mostly done, and I've glued in some blue 3 mm LEDs into the 9 pin tubes.I insulated the wires, and need to find out how best to wire these before I solder in those Russian PIOs (C5-Cool.

    pic: http://s867.photobucket.com/albums/ab233/markCNY/Pimped%20Dynaco%20STEREO%2070/?action=view¤t=photo.jpg

    The red is the long (+) side, the blue will be the short (-) side....
    Can I use the Stereo/mono switch to turn these on and off ? (it just a 2 way switch, correct?)

    Where is the best place to power from? (heater 6.3 AC, or is there a suitable dc supply to ride off of?)
    Switch the hot (+) side ?

    The LEDs: http://www.mouser.com/ProductDetail/Lite-On/LTL1CHTBK4/?qs=sGAEpiMZZMs4quMj8r4lmoAViFf0p1NLJrM3goEycIw%3d
    Thanks-

    Thanks-

    I'd like to have someone over my shoulder here, since I don't want to blow them up wiring them wrong, and having to de-solder, dig them out and start over.....


    4MarkNY

    Posts : 19
    Join date : 2009-10-13

    Re: VTA-70 LED wiring....

    Post by 4MarkNY on Thu Mar 15, 2012 7:09 pm

    Ok, If I have this right, and use the 6.3 Vac filaments, and the Leds take 3.5v, I'm not going to be able to run them in series.....I'll need about a 140ohm resister ( or close) on each each lamp leg from the switch. Please stop me if I'm off here....
    6.3-3.5= 2.8/.02= 140ohms

    http://www.kpsec.freeuk.com/components/led.htm


    Last edited by 4MarkNY on Thu Mar 15, 2012 7:38 pm; edited 1 time in total (Reason for editing : add info)

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: VTA-70 LED wiring....

    Post by Luddite on Thu Mar 15, 2012 7:53 pm

    Don't forget the diode. LED's need DC not AC current.

    Best Regards,
    Charlie

    4MarkNY

    Posts : 19
    Join date : 2009-10-13

    Re: VTA-70 LED wiring....

    Post by 4MarkNY on Fri Mar 16, 2012 9:16 am

    Thanks, Charlie.
    Will a single diode, say, before the switch, be sufficient? or do I need to build some sort of full wave rectifier circuit?

    Mark


    Don't know why the original response showed up as a new topic......copied into here...please eliminate the other to if you're a moderator..

    Thanks

    Mark

    anbitet66

    Posts : 132
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: VTA-70 LED wiring....

    Post by anbitet66 on Fri Mar 16, 2012 12:47 pm

    If you want to power your LED's with one of the filament taps, the math I came up with is as follows:

    1-Use a full wave bridge rectifier and a capacitor filter (100uF should be sufficient). This will give you about 7.5Vdc to play with; that is 6.3 volts times the square root of 2, then subtract 2 forward bias drops of the bridge rectifier (1.4V).

    2-Wire the LED's in parallel (each with a resistor in series). An LED draws approximately 10 to 20mA of current, so split the difference 15mA. Now take the voltage from above and subtract the LED's voltage drop of 3.5 volts, then divide by the current of each LED. 7.5v - 3.5v = 4v divided by 0.015mA. The math says about 266.6 ohms, so go to the next highest resistor, 270ohm 0.5 watts. If they aren't bright enough, you can safely drop each resistor to 220 ohms.

    The LED's can operate on AC, they'd just flicker, this way they will be lit solidly. I haven't tried this myself, but we're talking a couple of dollars of components and a few minutes to see if it would work. Assemble the LED's and resistors, connect them in parallel, then connect them to the filament pins of your front sockets (you do have front sockets complete with the correct wiring for a PAM1, don't you Suspect ? If everything is ok, the three LED's will light just leaving you with the job of installation.

    Phew. Nearly had smoke coming out of my ears on that one Razz

    Good luck,
    Tony

    heyraz

    Posts : 58
    Join date : 2011-10-26

    Re: VTA-70 LED wiring....

    Post by heyraz on Fri Mar 16, 2012 1:31 pm

    Any chance those flickering led's might introduce noise into the circuit?

    anbitet66

    Posts : 132
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: VTA-70 LED wiring....

    Post by anbitet66 on Fri Mar 16, 2012 2:35 pm

    I don't think so. But by using the circuit I described, the issue is avoided. The LED's will be operating on DC current, and the additional 50 to 60 mA will not have any effect on the power transformer.

    Tony

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