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Odd Tube Glow? (pic)

schmidlin

Member
Messages
5,257
So this bass amp snapped a fuse, but powered up after re-fusing (lol) and is now behaving perfectly fine, for now. But that tube in the middle has a red glow and not coming from the heater/cathode, and struck me as odd. Is this normal? Granted, it's a Chinese among the Tung-Sols. Also, it heats up like the others after 10 mins of playing, so I'm pretty sure it's working. Tia.

 

Jerry Glass

Member
Messages
870
If I recall correctly (Idon't have any Russian 6550s in stock to confirm), the Russian tubes have solid sided beam forming plates while the Chinese (I have these in stock) have beam forming plates with open ends on the sides. You are seeing the accelerator grid (screen) on the Chinese tube; orange is acceptable, yellow is not.
 

schmidlin

Member
Messages
5,257
Thanks for the replies...so screen grids glow? New to me, but I never really tried to notice.

Also, I tried no flash, it just turned everything orange, and I was hoping not to tear into this thing, but a I will if I have to. Just trying to find out what *normal* is.
 

Rambergwest

Member
Messages
914
Ifyou want to split the problem between tubes and components you can swap two of the power tubes and see if the same tube glows in the new location or if the previously normal tube suddenly changes. This says its the tube or its the circuit to this socket. Most likely you have a bad tube that would glow in any socket. Mike is right measure it if you really want to know.
 
Last edited:

Blue Strat

Member
Messages
30,192
Thanks for the replies...so screen grids glow? New to me, but I never really tried to notice.

Also, I tried no flash, it just turned everything orange, and I was hoping not to tear into this thing, but a I will if I have to. Just trying to find out what *normal* is.

Tubes with abnormally glowing screens draw excess current. Have you compared current draw between the tubes? If not, we're only guessing.
 




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