What I am asking is;
I have old electronic devices and I want to replace the guts with newer parts. for example; big resistor with a smaller modern equivalent. a flash tube with whatever will do the same thing.
so… where can I find information on how to find the modern equivalents of the old electronics? How do you know what to replace the part with?
for example; will a 1/4W 10K resistor from radio shack really work to replace a resistor that is rated the same but is three times bigger or does it only work in theory?

Let me clarify: Do all electronic circuits have electric equivalents?