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This topic comprises 2 pages: 1 2
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Author
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Topic: Exciter lamp to amp wiring
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Jeff Stricker
Master Film Handler
![](http://www.film-tech.com/ubbmembers/224.jpg)
Posts: 481
From: Calumet, Mi USA
Registered: Nov 1999
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posted 12-01-2002 07:40 AM
Hi Scott,
Well first I didn't realize this post had to do with an old phototube. So my first comment was misdirected. Sorry for confusion.
Anyway, with a modern solar cell, the cell wants to drive a resistor. I think that is because the cell sort of acts like a current source. Pumping current through the resistor, converts to current to a voltage signal which is what the input of a preamp wants to "see". I didn't know all this when I first started tinkering a few years back, until the learned folks here enlightened me. So I hooked up a resistor, voila! MUCH improvement in distortion, etc. I've used resistor values anywhere from 300 ohm to 1K-ohm and all work fine. I believe Paul Thompson has also experimentd with the same resistance values and has same good results. (Some of the commercial amp schematics I've seen, show a 680 ohm resistor at the solar cell input)
As to the capacitor, it is only needed if your preamp doesn't already have a blocking capacitor on it's input. The purpose is to keep DC voltage from getting on the first stage of amplification and upsetting the bias conditions, causing distortion. More than likely any mic preamp, etc. already has a built in blocking capacitor, so another would be redundant. Jeff
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