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. |
I agree with Brf. I've never seen anything I would call "red glow" from any of the 845s I've used in my SET monoblocks. Dave |
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?? |
Thank you Brf and Dopogue for your input! According to the manufacturer the dissipation rating for the Sino 845 is 70W. The amp is a self-bias so there is no need for adjustment. The tubes in question are Sino 845 (not B, C or W). I got the amp second hand with this type of tubes and I do not know if these tubes are the originals. I wrote to Bel canto about the dissipation requirement for the SETi 40 tubes but so far I have not received an answer. I should clarify that the red glow is present in 95% de the graphite plate, and after shutdown it last about 2 min. If I continue using the amp this way would I damage something? So far I have used the amp about 150 hr and I like it very much, I just noticed the red glow last night!! because I lisen music during the day. Thanks again for your help! |
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. |
Thanks again Brf. I just run into an article in VTV (vacuum tube valley) where it says "graphite es heat-resistant (in fact, it can operate with a dull red glow for a long time without failing)" in power tubes like the 811 o 845. However a new set of 845 tubes is coming my way. |
Red glow in morning, audiophile take warning! Sorry, sometimes I just can't help myself. |
I just got an answer from Mathew Cramer from Bel canto. He says that "the red glow is normal for this type of design" (SETi 40). So that settles everything down. Thank all for your help. Tiofelon. |
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. |
Good point Brf! He did not said anything regarding the low dissipation. I will ask him if the SETi 40 is biased for a standard 845 tube (100 W dissipation). |
I got another answer from Bel canto stating that the dull red glow from the graphite plate is normal and that the amp can drive just fine the 845 low dissipation tubes. Bel canto did not said anything regarding the amp bieas for a hight dissipation tube or for a low one. Thanks again Brf. |
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. |
Got an another answer from Matr Cramer at Bel canto. He says that "a dull red glow is normal for a 845 tube, but he recommends using a 845 tube with a 100W dissipation or they can fix the amp so that it can lower the dissipation rate as it prolongs the life of the tubes." So according to Bel canto and Brf the amp runs fine. It this the life of the tubes that is in danger of premature failure. Thanks Brf. |
