Well as a small update, my chinese 8 segment auto-ranging displays have failed me.
They came delivered with no datasheets which I thought was purplexing, but I continued designing my quad bias probe box anyway. They did auto range and measure their own respective 9V battery voltage correctly, so I did perform a function test of them individually upon arrival.
What I did not anticipate though, was that their range was stated to work from 0V to 100V. That to me meant they should measure 0.01 to 0.05 ranges just fine when in fact they displayed 0.0V the entire time. They couldn't register anything less than 100mV minimum.
I ordered a new box, new rotary switch, and supporting plug hardware to make a 4 way bias probe measurement tool that can utilize an external meter. I'll simply cut the probes off the current box (not worth the time to unsolder what is there) and re-use them as a pluggable probe into the box. In this manner, I will have the ability to measure anywhere from 2 tubes to 4 tubes at a time. The probes themselves will be modified with banana plugs so that any single probe can work with a multimeter.
It's a large setback on the bias measurement tool, but lesson learned. Keep it simple.
I need this bias probe so that I can bias the amplifier with the tubes installed, otherwise, my B+ voltage will be incorrect for the metro-loop install.
Anyway that's my update.
