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In Reply to: RE: Tung-Sol kt170 glowing issue posted by kkak66 on December 02, 2023 at 13:33:05
The tube glow is an "issue" very, very odd. Can I replace this tube and be in specs and all the chatter that goes along with this?
I think you're pushing it with KT-170's. What is your bias setting is it as low as the amp will go? If yes, then the bias is not negative enough to control that tube, and the others might be on the edge of stability.
Do this: Turn the amp on and darken the light in the room so it's at a candle light level, away from the amp. If one tube is glowing red and all others are not, you -might- be OK. If you replace the single tube it should test the same as the tubes you have, or you should replace the pair with a pair that's similar in test measurements to the two you don't replace.
The other thing you might consider doing is dropping to two tubes per side instead of 4, so two in push-pull configuration on each channel. That will at least tell you if the amp can be driven by KT-170's without the tubes getting too hot while in use. Keep an eye on them for any with red plates. Again watching the amp in dim light helps to catch an overheating tube early.
I see no reason to be concerned if you replace just one tube. If it needs biasing then do it. Do you have an extra? Did you move glowing tube to another socket just to see if it stays the same? If your worried just replace...-.im not an expert but I use all tube equipment and I do have all my tubes tested. Some filaments do very to some degree of brightness, but if it turns cherry red shut your amp off immediately.
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