Cant figure out how to post a pic so I will describe a mystery tube I came across in a box of old tubes. It is a four pin cylindrical shaped envelope with "Cetron" engraved on the base. It looks like it has some sort of paper inside with two of the pins attached to it on the bottom and one of the pins going up to the top of "paper". There are also letters and numbers scratched on the back of it-B13880. I cant imagine that it is paper. I do not get any ohms on any of the pins. Anyone have any idea what this is and how to test it and what it is used for?
Thanks,
Jon.

Could it be a photocell? Does the 'paper' look like half a cylinder? Is the 3rd wire a rod in front of the 'paper' that doesn't actually contact it?

If this is so and you can determine which pins connect to the elements within the tube, you should be able to get a small voltage when a bright light is shined upon it. You can also ohm it out by connecting the negative lead of your ohmmeter to the pin that connects to the 'paper,' which is the cathode, and the positive meter lead to the rod, which is the anode. With your ohmmeter set to its highest setting, resistance should change when light is shown on the phototube.

T.

:Jon from Louisville?

::Jon from Louisville?
:
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Thomas/Phil,
Yes to both. How was the tube used and how do you test it?

Typically photo cells were used in motion picture projectors for the optical soundtrack pick-up, but had other uses, such as automatic doors, elevators, and automated assembly line devices, and on and on.

All of my sound projectors have one, but it's the really small 3 prong type.

I'm not sure what the method is for testing them. Perhaps either there is a specified voltage output for lumens received, or something like that. If you can get your meter to deflect when light is shined upon it, then it's probably alright. Extremely bright light for long periods of time, or excessive voltage causing ionization of any gas present inside of the tube will damage the photo-emissive coating. One of my projectors has a photocell voltage adjustment, and the instructions specifically warn against excessive voltage, but this can be easily heard as a rushing sound in the speaker.

T.

:Typically photo cells were used in motion picture projectors for the optical soundtrack pick-up, but had other uses, such as automatic doors, elevators, and automated assembly line devices, and on and on.
:
:All of my sound projectors have one, but it's the really small 3 prong type.
:
:I'm not sure what the method is for testing them. Perhaps either there is a specified voltage output for lumens received, or something like that. If you can get your meter to deflect when light is shined upon it, then it's probably alright. Extremely bright light for long periods of time, or excessive voltage causing ionization of any gas present inside of the tube will damage the photo-emissive coating. One of my projectors has a photocell voltage adjustment, and the instructions specifically warn against excessive voltage, but this can be easily heard as a rushing sound in the speaker.
:
:T.
:
See what you can find on a RCA 930 tube...sticks in my mind as a tower light controller at a radio station I worked at long ago.
Lewis

Lewis,

I think you are probably correct. I also want to think this tube was used in some tower lighting controls by the US Army Signal Corps at some of their comm sites back in the 60s and 70s. Also remember the controller had a gear motor with a cam of sorts that rocked a mercury switch back and forth to control the beacon on top.

Clifton

::Typically photo cells were used in motion picture projectors for the optical soundtrack pick-up, but had other uses, such as automatic doors, elevators, and automated assembly line devices, and on and on.
::
::All of my sound projectors have one, but it's the really small 3 prong type.
::
::I'm not sure what the method is for testing them. Perhaps either there is a specified voltage output for lumens received, or something like that. If you can get your meter to deflect when light is shined upon it, then it's probably alright. Extremely bright light for long periods of time, or excessive voltage causing ionization of any gas present inside of the tube will damage the photo-emissive coating. One of my projectors has a photocell voltage adjustment, and the instructions specifically warn against excessive voltage, but this can be easily heard as a rushing sound in the speaker.
::
::T.
::
:See what you can find on a RCA 930 tube...sticks in my mind as a tower light controller at a radio station I worked at long ago.
:Lewis
:

Thomas,

Your 3-pin mini photocell was/is probably the #927 tube.

Clifton

:Typically photo cells were used in motion picture projectors for the optical soundtrack pick-up, but had other uses, such as automatic doors, elevators, and automated assembly line devices, and on and on.
:
:All of my sound projectors have one, but it's the really small 3 prong type.
:
:I'm not sure what the method is for testing them. Perhaps either there is a specified voltage output for lumens received, or something like that. If you can get your meter to deflect when light is shined upon it, then it's probably alright. Extremely bright light for long periods of time, or excessive voltage causing ionization of any gas present inside of the tube will damage the photo-emissive coating. One of my projectors has a photocell voltage adjustment, and the instructions specifically warn against excessive voltage, but this can be easily heard as a rushing sound in the speaker.
:
:T.
: