My Sanwa PC510 multimeter has the capability to measure the temperature via small probe. So, I’m curious to measure my tube glass/surface temperature. I test the 6N1P, 6N6P, and 5U4G tubes.


The result is quite acceptable. I mean, acceptable hot 🙂

The 6N1P surface temperature measured around 60 degree Celcius. It’s a small 600 mA filament.

The 6N6P and 5U4 got quite high, could reach over 75 to 78 degree Celcius.

This 6N6P consumes around 900 mA while 5U4 around 2A current, but both got similar surface temperature. The reason is, 6N6P is on a smaller 9-pin socket, while 5U4 is on the bigger Octal bottle. So even higher 2A current on 5U4 produces lower surface heat. Also 6N6P is a very hot dual triode up to 8 W plate dissipation.