6550 replacements for upgraded CD7

Is it OK to use any 6550 equivalent (KT88, KT90, etc) in an upgraded CD7 power supply?
Quick after the upgrade of the powersupply I put in a 6550 Tungsol black
plate . Wow it still works for years without any problem . After buying the CD 7 I replaced all the small tubes by 6H30P-DR versions .Still in use , also a big improvement .A problem prices for the Tungsol and DR are very high . 

Glad to read that you had good results in switching the 5881 for a Tungsol 6550.  That said, I am surprised you did not damage the CD7.  

Did you check with ARC as to whether the 6550 is an appropriate tube roll for the 5881?  FWIW, I used to own the CD7 and since moved up to the CD8, which uses a 6550 in its power supply. It never occurred to me that the 5881 was interchangeable with the 6550.

Just askin' …...
hello bifwynne , no I did not ask ARC , I followed the advice of a university graduated engineer who is doing business in the Netherlands
with his own brand of CD players , amplifiers and other highend products . The 6550 NOS tungsol was installed in 2009 , and is still working . BTW I installed this tube also in my REF 3 SE , I made my REF 3 a home SE version by the capacitor upgrade . All upgrades and mods in my PH 5 ,
REF 3 and CD 7 have made a big improvement , so I did not have to buy new units . I like ARC very much but in my opinion and the Dutch designer the units could be  much better by some improvements.