Logic circuit to detect loss of voltage

[iamnothim]

In my tube tester project 2 out of 3 tests operate. the 3rd is the "Shorts Test"
An indicator light T3 1/4 90V should come on when one of the pins of the tube under test has a short.  In the test circuit there are 6 pins bussed together, if the buss breaks the light should go on without pushing any buttons.  The bulb is good.

This got me thinking.  Is there a little logic component that could monitor for loss of voltage and close a contact, illuminating a light / LED?
I suspect I would have to bring the voltage way down.

I'm barely able to work with resistors and capacitors.  I have no idea how to program and implement something like that but I think it would be more reliable solution.

Any comments or direction will be appreciated.

Thanks

[jpb]

why not just use a relay? Assuming you want it to operate at 90V and you want it to detect a complete loss of voltage.

Otherwise you could use a resistive divider and a comparator with some other fixed voltage (if the fixed voltage was also 90V you wouldn't need the divider).

Or perhaps a bit more fun would be an electromagnet, a hammer and a big switch

[Gall]

For higher voltage, one of many good solutions is resistive divider with an optocoupler.
For lower viltage, just a divider driving a transistor or a logic gate.

[iamnothim]

Thanks for the ideas.

The hammer is a must have, but not for the circuit.