Is the red glow normal for 845 tubes?

I can only go by my own experience using 845 tubes by Amperex, United, Metal plate 845W, 845C, 845M, and the Shugaung 845B and standard 845. You should not witness a red glow when the tube is powered up. If the red glow can "fight" though the sea of white light, the plate is too hot. Once the tube is powered off, the plates glow red BUT the glow should not last 25 minutes!!! The red glow in my amps may last a minute.

Sorry Tiofelon, I misread your post and noticed that your tubes glow red after 25 minute of being powered up and a couple of minutes when powered off. This is still not normal for a standard 845. What is the Sino 845 dissipation rating? Perhaps it is a lower dissipation 845 (around 65w-70w) and your amp is designed for a standard 845 dissipation tube. Most graphite plate 845 tubes conform to the RCA standard with some carbon plate and some metal plate variants having a lower dissipation rating. Are the tubes biased correctly??

The Bel Canto amp is designed to run the 845 tubes at the NOS RCA standard dissipation of 100w, therefore, you are running the Sino (70w) low dissipation tubes 40% over their optimal operating rating, which accounts for the red hot spots on the plate. Red hot spots on the plate are a sign of an over driven 845 tube. You will not harm the amp, but the tube life will be significantly shortened. You have 3 options 1) run the current tubes until they expire 2) change the tubes to a higher dissipation 845 3) have the amp modified. I would opt for #2.

What did he say about using a low dissipation (70w) 845s in the SETi40? That is the real question you should ask. If the SETi845 is auto biased for a standard 845, then the amp is over driving the Sino.

Hi Tiofelon, Bel Canto's response has me puzzled. The SET40i is auto biased, therefore, it is either optimized for a 70w dissipation or 100w dissipation, it can't be both. If you are still curious, check with Bel Canto to be sure of the dissipation/op point. Ask what's the auto bias setting (in ma) and ask what the plate current is in volts. Once you know these two figures, you can calculate the tube dissipation. (plate voltage x plate current in ma = plate dissipation in watts. e.g. 1000v x 100ma = 100w ).

Yes, a "dull" red glow in an 845 is normal, but a prominent red glow indicates an over driven 845. As mentioned before, you are not hurting your amp.