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Life of KT150 tubes on ARC Amps

I have Audio Research 250SE amps and the tubes in it have 2400 Hours. I wanted to hear experience from other ARC users if they replaced KT150 tubes before 3000 Hours.  I am not sure if i need to replace them now or wait for some more time.   I dont have new set of tubes for me to compare with my current tubes and wanted to hear from other people who replaced the tubes.

veerapaneni
jea48
4,613 posts
 
fsonicsmith322 posts02-01-2019 9:44am

It is no secret that ARC feels that fuses and other methods of circuit protection degrade the sound and also no secret that ARC’s practice of having a single resistor act as circuit protection for tube failure is a pain for the customer. If a tube fails, the resistor not only needs to be replaced but on occasion there can be more damage to the circuit.

Older ARC amps are not user friendly when it comes to biasing of the power tubes, that’s for sure.

As for the screen resistor that blows if the power tube runs away I find it hard to believe ARC didn’t know when the resistor blows, burns/blows apart, from being over loaded that ARC didn’t know the event could cause damage to a circuit trace.

It’s just common sense the resistor should not be installed close, tight, against a circuit trace on the circuit board. At the very least a fire rated insulator should have been installed between the resistor and the circuit trace to protect the trace from being damaged in the event the resistor blows, burns, explodes, apart. In fact the resistor should not be installed against the circuit board as it is. At the vary least it should be at minimum 1/8" from the board for even cooling around it. When you are pushing the amp, the tube, that resistor can/does get physically hot.


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veerapaneni OP
108 posts
 
I have get around 123 Volts and i bias my amps every few months.
johnss
593 posts
 
I would be surprised if the KT-150s are worn out after 2400 hours. 3000 to 4000 hours may be a better point to pull and test.

If you are that concerned why not get them tested. I use KT-150s on a daily basis and have periodically tested them. Quite a ways from wear out.


joecasey
484 posts
 
From what I heard, ARC recommended tube hours is based on performance and not tube life.
david12
1,454 posts
 

I am very happy with my 75SE, which has been upgraded to SE status for at least 3 years. I haven't replaced the tubes and have no idea how many hours they have on the clock. I listen a lot to my Stax l700 ear speakers anyway, so don't believe I am over 2000 hours.

 I have to say that the numerous stories of damage when a tube blows, do concern me. Are there any other clues to near failure, such as wandering bias? It would be nice to change them just before one blows. My amp only has 4 tubes, but they are still costly when you have retired.


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