So here's the problem with using expensive, rare, NOS 6550A tubes in the power supply of certain ARC Ref line stages and phono preamps. The 6550 output tube used in the Ref line stages and phono preamps are run hard and hot. ARC recommends replacing them at 2,000 hours. I had one 6550 blow well before 2,000 hours which necessitated a return of my Ref 6 to ARC for repair.
When I was talking to a tech at ARC about the repair,he recommended replacing the 6550 at 1,000 hours to prevent future problems. I took his advice seriously and I change out the 6550s in both my Ref 3 phono preamp and my Ref 6 every 1,000 hours.
I'm sure someone will make the argument that old production 6550 tubes were built much better than current production Sovtek NOS 6550 tubes and their tube life is much greater. In your case, did you buy your WE 6550 as NOS or was it sold as "tests like new"? How many hours have you put on the tube since you bought it when you were using it in your Ref 5SE?
The bottom line for me is that it doesn't make sense to seek out old, expensive NOS 6550 tubes to use in the power supply of the ARC Ref gear that uses them. Now if someone comes along and says they have been using expensive NOS 6550 tubes in their ARC Ref phono preamps and lines stages and they are getting 5,000 hours out of them before they change them out, I might be interested.
I have several NOS RCA 6550 tubes in my stash of tubes, but I can't bring myself to run them hot and hard in my ARC gear just to pull them at 1,000 hours.
