Nixie Bargraph. Works analog, like a voltmeter. Only two connections!!! It is of amazing simplicity. The higher the voltage the longer the lightbar. It is so easy to make a tube VU meter from this! I have tested it, and light intensity stays the same at higher voltage, only the bar gets longer. Very nice linearity. Don't know how they made these, but it works perfectly.
To get it working on a tube amplifier is very easy. These devices need high DC voltage, which varies with the AC signal. BUT you already have very high AC signal at the primary side of your output transformer. How to make DC voltage from that, we don't need to tell you?!
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