ARC Ref Anniversary preamp and Reference 10 come with a pair of Sovtek 6550 tubes in the PS. Did anyone experiment with these tubes trying to use alternatives such as KT88, KT90, KT120 or even KT150? Ever since I bought my Ref Ann I never bothered trying anything different other than the Sovtek 6550. Does anyone want to share their experiences? Did anyone switch the Sovtek 6550 for a better alternative and stuck to it?
I own an ARC 40th Anni Preamp and two friends of mine own the ARC Ref 10 preamps.
We tested diff contemporary and NOS tubes on our preamps and all of us think that the NOS tubes are the best performers.
The very best replacement for the original 6550 is definitely the Tung-sol black-plate made in 1950s.
The second best is the Tung-sol grey-plate made in 1960s.
We also bought and tried the popular NOS Winged-C 6550 but found that it was far inferior to the above two tubes.
The 6550 supplied by ARC may have been burned-in/tested/matched so they are reliable but sonics-wise they are many leagues below.
The problem is that ARC40 & Ref10 both need a pair of 6550 and the black or grey plate are quite rare. It's not easy to find a matched pair of good quality so we stock up spare pairs.