6550C vs 6550EH in Audio Research amps

Hmmm..., Yes, I'd also like to try the 6550EH. I just used the newly relabled 6550C from SED (the company formerly called "Svetlana"). One of the tubes was apparently poorly made and after use for a while, it suddenly shorted internally. It fried several of the parts in my ARC VT-50 when it lit up like fireworks. I'll probably try the EH when my amp returns from an expensive repair. :(

Holos

My experience is with a pair of ARC VTM 120 monoblocks that ARC tubed with the Sovtek 6550"B" tube. back in the mid 90's. Later they went to the "C"..but I think for all intents and purposes it may sound quite similar. I tried matched quads of the 6550EH tubes sourced from the tube store just before selling my amps last year. I felt that the EH's were somewhat rolled off on top and thought I may have lost some definition over all. After about a month, I put the stock 6550 Sovteks back in and was more satisfied with the sound of them in the end. Just my experience FWIW...enjoy!