Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: cspar on April 29, 2022, 07:56:50 pm
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I have an RCA 921 gas filled photocell that came off an old projector.
Although how is a mystery that I may never understand... I do understand that the photocell read the audio from the film strip and fed it to the amplifier.
Looking at the datasheet I see that when the photocell sees light it passes more current and the resistance increases.
I've heard of optical limiters in bass amps before but not looked into it. I'm wondering if it was done with these kind of tubes?
Can anyone point me in the direction of designs that use these tubes in general?
I've been having a hard time searching for stuff and just wading through nothing but typical LDR designs with no tubes.
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> done with these kind of tubes?
No.
The gas photocells were very specialized to the pick-up of optical film tracks. Not to control level. And any possible use has been totally over-taken by opto-diodes.
"Photo-conductive cells" are very different.
I have no clue why eBay is asking $51 each.
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Thanks for the info Paul.
I might still mess with it a bit in the future and see if I can figure out an audio application for it.
Either that or sell it on ebay.
Thinking about it they might be unobtainium for film folk like some BB chips are for us audio people.
On that note if somebody needs it for a projector. I'm down to trade for something that you have an abundance of.
I've been looking to salvage a saturatable reactor from a hammond organ for over a year now... I'd love to trade for one of those or learn how to wind one.