ARC VT100 with KT-120 tubes ?

Well the bias setting is the same as with the 6550. I can tell you it's at the very least an improvement in power output. They sound very good. No down side. I've only heard them in a pair of Ref210's.

HI,
Power of the KT-120's abilities relative to the 6550's are theoretical differences. The KT-120 is capable of handling more power but only if the power supply voltages are increased. When plugged in as a 6550 replacement and no other changes are made, the amp will put out exactly the same power. No tube will allow ohm's law to be revoked. I'm afraid that the issue of replacement is misunderstood.

Thus, power should not be the reason to replace the 6550's. There may be other reasons such as added lifetime because the KT-120 is working under it's maximum power output that is an advantage. But, not power.

I do not know what Hifigeek1 was hearing. Imagination?

Sparky

I wouldn't expect the tube change to make the amp put out more power. My interest is in longer tube life. And, I'm interested in knowing if there are sonic differences within the power limitations of the amplifier. In other words, will they last longer, and will they sound different (better) ?
thanks for your responses

Karma16. The KT-120 draws a bit more heater current per tube. There are possibly other variables with the KT-120 that I am unaware of... The Ref210's are mono blocks and are rated at 210w across 8 ohms with 6550's @ 120Vac line and that's what I measured. With KT-120's approx. 250w across 8 ohms with the same line voltage. I verified this on my service bench using a Dale 250W 8 ohm non-inductive wirewound resistor. Bias was the same as was plate and screen voltages. You can contact Audio Research and they will give you the before and after wattage outputs for 6550 vs. KT-120, just specify the amp in question. I fix their products in warranty.