audio Research REF 110 and KT 120 tubes

I spoke to K(C?)alvin the other day w/ regard to my CD3 and I asked about the KT120 for my VT200MKI. He said that first the KT120s are in short supply and they are using all they have for their current production. He did say however, that they are planning to determine which previous amps will allow the KT120 to fit and can be properly biased. He seemed to imply that the "modern" amps would not have bias issues if there is room for the tubes. He also stated there was a roughly 20% increase in power over the 6550. They are working on a new website but his advice was to be patient. If the KT120 will work in my VT200 I'll just suck it up and send it back to ARC and let them get it right.

Great tubes! I'm using them in my DIY PPPdiff mono-blocks. These amps use 4 output tubes in a "forced" class A push pull differential mode (the 2 pp halves are in series, nor parallel like class AB1 and cannot operate out of class A). Operating at 40% of plate dissapation as opposed to 85% with 6550s in these amps is a real benefit. I have experienced one instance where aKT-120 opened and stopped working requiring the replacement of a matched quad. That's better than the time a 6550 arched and turned a tantalum grid-stopper resistor to charcoal. ;~)

The KT-120 actually can run at a maximum plate voltage of 700-800Vdc! This is a very very robust tube. I have fitted a set in one ARC amp in warranty. It is taller, heavier, and the glass is thicker. Also on inspection, the plate of the tube utilizes heat sink fins. This is a very different tube then a 6550 and frankly sounds wonderful. I believe this currently represents the state of the art in tube design. Remember, unlike the U.S., the Russians never stopped making and designing tubes. That being said you will always get a random bad tube. It's the nature of the beast...

Hifigeek1...is there only one supplier of the KT-120s? From my conversation with ARC, they said they are not selling the KT-120s on a standalone basis for existing customers to retube their current production amps because they barely have enough supply to meet new amp deliveries that come with the new KT-120s. So it sounds like supply is pretty limited. Did you get yours from ARC or from a third-party tube vendor? Thanks.

Wow I guess my last post never made it on here. Cmalak, the reason I saw the KT-120's is I had to service in warranty a pair of Ref210's and they came with KT-120's. Understand that I can get KT-120's but they would not be ARC KT-120s. ARC runs all their tubes at hard labor for 24 hours to cull out the bad ones and then categorizes them based on their current gain etc. That way when I order tubes from ARC I have to give them the model of the product I'm repairing. Also, if any damage is caused by the ARC tubes within the warranty period, i.e. a screen or plate load resistor failure, it's covered under warranty. This tube represents the current state of the art in Russia tube design. You can email me gary.mf1@gmail.com and I can keep you updated as to when they will be available. Please be patient. Both myself and ARC know that people are chomping at the bit to get these tubes in their amps. This tube is so new they don't even know which amps these tubes will fit in. I just found out today that the KT-120's will not fit in the VT-200 as there's just not enough space. I can tell you that after just working on a Ref 110 the KT-120's will fit, and the factory tells me they work great! Additionally, any ARC amp that uses a 6550 regulator, that tube is not replaced with a KT-120.