Film-Tech Forum ARCHIVE: Kelmar exciter supplies and changeovers

This is topic Kelmar exciter supplies and changeovers in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Bernie Anderson Jr (Member # 410) on 05-14-2001, 11:49 PM:

Here's one that I couldn't figure out today. I was wiring a Kelmar Exciter supply to my projectors. I'm running twin machines with exciter sound changeover (double pole/throw switches). Well, get this, when I switched at either machine, the exciter supply would make a whining sound. The same sound as when the supply turns on. It dove me nuts. When you changed over you can see the little LED on the supply dim as if it was having a hard time lighting up the bulb. The DC current adjust was turned all the way up too. It doesn't make a sound in AC backup. I hooked the projectors up to my Kniesly power supply (Big black box model) and it seems fine, which leads me to believe that all exciter supplies are not built the same and with the newer ones not designed to run changeovers. Have you ever come across this? What's the correct DC voltage that the bulbs should be running at? Thanks

Bernie

Posted by Paul G. Thompson (Member # 655) on 05-15-2001, 12:16 AM:

Bernie, I presume that the exciter lamp will not come on in the soundhead.

Take an exciter lamp and some alligator clips and see if the power supply will light the bulb while you have the exciter lamp sitting on the table. If it lights up properly, you have a problem in your wiring to the exciter lamp holders in the projector. If the exciter lamp will not light, the power supply probably is kapoot!

Some exciter power supplies want to see an exciter lamp that is not grounded in the sound head. The "whining" is probably caused by the power supply outputs being shorted through the grounded side of the exciter lamp in the soundhead.

Reverse the output polarity of the exciter power supply, and see if it does the same thing.

What kind of soundhead are you using? And, what is the model number of the exciter power supply? Is any of the exciter power supply outputs referenced to ground, or are they floating? (kinda like a balanced output).

I run my exciter power supplies at about 7 to 8 volts. When you get it running, be sure to run Dolby Tone and calibrate your optical pre-amp in the processor.