Retubing an ARC VT100 mkll

So the verdict after decent breakin time- they're pretty good. Not what I would call a flat out night and day difference but a bit more "drive" and a little less glare in the upper ranges especially when the volume is turned up. All in all I'm pleased for the $450 spent, but I will give full props to the EH6550 tubes - they were a good value. Assuming I can get 2 years out of the KT120 set, I am happy with the change over. BTW, one big physical difference is the heft and weight of the 120 vs the 6550. These things feel like they're built to last. Cheers!

Just a footnote comment about the KT-120s. I had about 3000 hours on my KT-120s and thought it might be a good idea to retube my amp. I bought a complete set of tubes from Upscale Audio and dropped them in. The price is about half what ARC would charge. Kevin Deal burns in his tubes for 72 hours before matching and then checks three electronic attribtes: bias, G2 and transconductance. After about 20 hours of break-in, it's quite obvious that the amp sounds better. FWIW.

Btw, one of the matched sets did not take a bias adjustment. I put an old tube back in and everything was ok. Called Kevin. He immediately shipped out a replacement matched tube. Everything is now good to go!!

Wow 3000 hrs. is well passed the recommended ARC replacement time. I would say you got lucky..

Gary, I'm sure you're right. But I wonder if the KT-120s are as susceptible to arcing or other malfunctions that would damage the amp as compared to the 6550 C tubes. The build quality impresses me that the KT-120 may have a longer life than 2000 hours.

I can tell you, they're still susceptible. If your amp was wired in triode, you might be able to get away with it.