Life of KT150 tubes on ARC Amps

@ veerapaneni

One thing you might want to check is the AC mains voltage at the outlet/s the amps are plugged into. The mains voltage can affect power tube life. Power tubes will last longer if the mains voltage is, say, 117Vac than if it is 123Vac. Check the mains voltage at the wall outlet/s with the amps powered on. Higher voltage increases the tube filament voltage as well as the DC power supply voltage.

Say the voltage measures 123Vac - 125Vac. You may very well be at the end of the tube life of the KT150 power tubes with 2400 hours on them.

Also worth noting, how often do you check the bias for the power tubes? Listening hours of use between checks....


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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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I have get around 123 Volts and i bias my amps every few months.

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.

From what I heard, ARC recommended tube hours is based on performance and not tube life.