Tung-Sol kt170 tube started glowing brighter

I installed 8 Tong-Sol kt170 tubes in my Sonic Frontier Power 2 amp. One tube started glowing a bright orange, yellow at the lower portion. I hear no sound interference. Should I replace it? If so, replace paired, right channel quad or all eight for matching purposes? I did swap the tube into different socket and it is the tube.



I have never used KT-170 tubes only the KT-120. Perhaps you can find a used KT-170 with low hours on it, I would definitely replace the one that you describe is glowing different than the others.

Somewhere down the line, if you keep that amp perhaps convert to KT-120's they put out less power but are cheaper and perhaps more reliable.


Have you biased your tubes? Is your amplifier capable of accommodating the KT170? @ozzy has a point and KT120s maybe better suited for your application. I have had no issues running any of the KT series valves, 88, 90, 120, 150 or 170 as my amplifiers are built to accommodate operation with any of these tubes. Have you tried swapping this tube in another hole to see if it lights up like it is in the current position. If so it may be a bad tube. If not check you may have other issues. 

Your amplifier is rated for use with either 6550C or KT88 output tubes. It is not designed to handle the current draw of the KT170 output tube. In addition, as previously mentioned, your amplifier requires re-biasing when changing output tubes. I would heartily recommend pulling the KT170 tubes before the amplifier goes up in smoke.

The designer said the KT170 tubes would work. They are a new tube to the market. These were brand new and played for 50 hours for this to happen. Of course I biased the tubes. I’m pulling the amp and placing my solid state Arye amp back in. I’m almost positive I’ll go back to KT150 tubes. I don’t hear the prat that I got when I had KT150 tubes installed. They needed replaced, hence here I am.

I don't know tubes to this extent. This is why I posted. I do know that a repair of the amp is forever and $$ so I'm reaching out for help.

KT170 tubes have been around for several years. Have you moved that tube to another hole to see if it is the tube or your amp? 

Yes, the tube was moved and I can confirm it is the tube. My question is about matching and all the numbers that that go with that. I moved the tube, I biased all tubes and googled a lot. Can I replace the one tube I buy to replace the bad tube and bias the 8 tubes over again and be where I should be at a great result?

I would just buy one tube and pray for the best, keep the bright one as a backup. If purchased new you should have a 30day warranty I am sure you are past that. 

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Don't reuse the tube that glowed red (not worth the risk).

Pretty certain the P2 has individual bias adjustment for each power tube and if this is the case pick up a new replacement and bias it per SF's instructions.



@kitegod , Yes, you can replace the one bad tube with one with similar numbers on it and then check / reset bias. If your amp isn't rated for the KT170 despite being told it should work it might be safest to revert to the tube types that are specifically compatible with the amp? I guess the other option is get the new KT170, install it, check bias and see what happens- it may have been an isolated incident with the one bad tube. 

@OP The tube is starting to red plate. Don't try to rebias the tube as it will only hasten it's demise.

With only 50 hours on the tubes why not try to get a warranty type replacement from seller?  It sounds like you were sold a bad tube.

I'm pretty sure you are seeing an event called "Red Plating" which is the tube overheating. There are a few causes- and finding them can be a mystery. 

The tube could be shorting (doubtful given what you've described)

The bias is certainly off. How could I know that? All biases are off at least a little. Add time, other component deterioration, and mismatched components and it's a boas nightmare. 

I had a mystery red plating problem and it turned out to be a bad 12BH7 high current driver - which caused me to have to replace 2 6550s. OUCH!