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Old 08-26-2017, 09:45 PM
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maxhifi maxhifi is offline
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16mm projector amp

Anyone have experience working on optical sound? Specifically, how to test the phototube, and how much background hiss is normal.

I'm working on a devry 1966 amp, from 1946, or 1947. Everything works good, it had some noise which was caused by the resistor giving DC bias to the photocell. Replaced with metal film and that's gone.

The photocell itself is insanely sensitive, incandescent room lights will give a loud and clear 120Hz hum, heck the 6W threading lamp in the projector added so much noise I had to just remove it. What I want to know about thoigh is hiss - how much is normal? You sure can't notice the hiss while a movie is playing so it's probably academic at this point, but what's good can always be better.
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