Electron tube operation with 250mV anode voltage?

The 7586 Nuvistor electron tube still operated with a little gain at 250mV anode supply voltage.


Although at 500mV the sound gets like a good quality telephone for some strange reason at Vb approx 250mV the sound gets more body. It is a colored sound like ADT with a few milliseconds of delay, like phasing. Like the oldie song Crazy Love.


Setup, signal path:


MD211 - Pleuades V6 - Sony .... (see next posts)


At less than 150mV sound output almost fades away.