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Flourescent Display on Betamax

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cstroh

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On an SLH500 Betamax, there is what is called a flourescent display. It appears that the filament voltage is 3.7 VAC but all other voltages are negative, with -22 volts being the most negative. How does this work, I would expect positve voltages to attract the electrons off of the filament?
 
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On an SLH500 Betamax, there is what is called a flourescent display. It appears that the filament voltage is 3.7 VAC but all other voltages are negative, with -22 volts being the most negative. How does this work, I would expect positve voltages to attract the electrons off of the filament?

Your mistake is assuming absolute voltages, there's no such thing - all voltages are relative (to where you measure it from).

In this case the cathode is negative of the anode, which is exactly the same as the anode been positive of the cathode, just a question of where you measure from.
 
Thank you for the response. I agree that voltages are relative, but let me describe further the voltages. Using a common ground, the filament measures a -17 volts DC and 3.7 volts AC. What I think are the inputs to the display are all negative DC values ranging from -2.0 volts DC to -19 volts DC. Some of the inputs labeled as "S0" through "S15" are tied by 100 k resistors to a line at -22 volts DC. I attached the Sony schematic to this thread but do not know if you can retrieve it. If the filament is the cathode at -17volts, it appears that the anode is even more negative. Some where I am looking at this wrong because though dim, the display still works. Again, thank you for your input.
 
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The filament doesn't have to be the cathode, and only is in directly heated devises.

To pass current the anode needs to be positive with respect to the cathode, and the grid needs to be within a certain range (negative or positive) of the grid, depending how much current you want to flow.
 
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