[Tubejunke]

I want to see if I can simplify this cathode current thing and test my own understanding at the same time. An electron tube in it's most common form is a triode or three section tube. I am using the triode for the sake of simplicity. There is a cathode circuit, a plate circuit, and a control grid circuit. So, given three sections there are three circuits involved in order to bias (provide a difference of potential or voltage) each of the sections.

So, if we were to want to measure the current flowing through any of these sections, we would have to break the circuit, and I don't think that it would matter where except within the tube its self which would be impossible. Once the circuit is broken, an amp meter would need to be connected in series. I must stress the fact that the meter must be IN SERIES, like part of one of the wires more or less, NOT parallel!!!

With all this being said, we should now be able to tell how much current is running through the circuit with no problem. So, in order to create a remote test port you would simply extend one of the wires feeding the cathode portion of the tube to an easily accessable location and create a method of easily breaking the wire and ineerting the meter. Then you want to be able to easily reverse the procedure and remove the meter, then provide a good re connection.

I am thinking that when designing this the best idea for me at least would be to install a glass fuse holder. Remove the fuse, perform the test, then reinsert the fuse. The fuse will provide protection from over-current so you won't need to worry about it anymore.

If you want to get really fancy, you could do the fuse holder AND a stand alone analog (or digital) milli-ampere meter. They can probably be found for sale on Ebay or possibly even some electronics supplier. A final thought for me is the use of an industrial motor over-current device, basically a breaker with a switch knob. Nice and reliable and you never buy fuses, but probably not cost effective.

So maybe this will help some as there has been some confusion on what to do here and it is a rather important issue from all I have ever read or heard. I don't have a schematic to elaborate on pin #s or any of that. I hope also that my take on this is correct.