Life of KT150 tubes on ARC Amps

I know man, Roger Modjeski and The Band, my two crusades. Also Bruce Thigpen and Iris Dement. I shall attempt to curb my enthusiasm out of consideration for ARC apologists, if for no other reason. Before I do though, I wonder how many have actually heard the RM-200 Mk.2 or Eminent Technology LFT-8b? Brooks Berdan enthusiastically recommended both to me, but that was on a friend-to-friend basis. To his paying customers he sold Jadis, VTL, and Wilson. WAY more money to be made selling brands with audiophile cache’ and bragging rights. Higher price = better sound? I have no doubt that lots of people dismissing the RM-200 Mk.2 (particularly in comparison to the REF 75SE/150SE) have never listened to the amp. They just "know".

Oh no, I forgot to mention one thing. Last one, I promise. Brooks wasn’t an ARC dealer (he had sold the brand when he was at GNP in Pasadena in the 80’s), but he loved having customers who owned them. He sold them a lot of RAM tubes, and also made money repairing them everytime a power tube took out some parts when it blew. The shelves of his used equipment racks were full of ARC power amps, everyone of them having scorched circuit boards. The brand reminds me of not Porsche, but Fiat ;-) .

Well, we have Iris Dement in common. Tis a shame she has put out so little music. 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. For the most part, this is a thing of the past, but it was a huge problem back in the 90's. I don't think that there is anything magical about my Ref 150SE and I have no doubt that any number of competitor tube amps including the RM-200 equal or exceed it. I do believe that the ARC Ref 6 and Ref 10 preamps are among the best five preamps currently available. My Ref 6 makes me smile every time. Huge soundstage and a magical quiet forcefulness. I am one of those who believe the preamp is the single most important piece of electronics and is the heart of any system, more so than the amp or speaker. My choice of amp simply followed my choice of preamp. They match and are compatible though any number of other tube amps would also work well. 

@ 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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