Why? -Only the different ratios of both opt?Lundahl 1660 / 10ma 4.5: 1 Alt Q or LL1692A / 10mA 3.5: 1 would be suitible. But the LL1692 has slightly more output impedance, but more gain.
thanks for all interesting answers.
i think the small filament current ou 0,13A ist perfect for battery supply, isnt it?
What are your opinions for battries? (low noise und hum)...
Why? -Only the different ratios of both opt?
I agree, the 31 makes an excellent preamp tube. I was positively surprised. I still prefer the 10Y overall but the 31 comes close. I prefer it over the 26
I have used several 31s in the preamp I built, no issues with microphonics. With clean filament and B+ supplies there will be no hum. The tube is not more or less susceptible to hum than others.