6550 replacements for upgraded CD7

Hi, just to align the discussion with my other thread, the use of the 6550 was real life tried by some EU audiophiles and for them it has been working flawlessly.
Nevertheless, not wanting to breach any ARC policy, I'll have a word with Calvin on this topic before I proceed.

On a slightly different note, as this tube goes in the power supply section, how important is it, sound-wise, to go for some fancy NOS tubes other than modern, cheaper, models?

Cheers.

I discussed this with Leonard a number of years ago when I sent my CD7 in for the upgrade. The upgrade at that time was free if I remember correctly. I was told that the reason for the power supply being upgraded was that there were problems with some of the 6H30 tubes aging differently. This could cause reliability issues as well as other problems in the power supply. That is why the 2 6H30 tubes were replaced with a single 5881. The reason that the 5881 tube was chosen instead of a 6550 like in the CD8 was space. There was concerns that there would not be sufficient clearance for ventilation using a 6550. This could cause heat issues as well as the possibility of shortened tube life.

Since the 5881 is a pass element in a regulated power supply, I doubt changing it would offer much sonic improvement. You can always try an NOS, but it must fit properly and allow for proper ventilation, or problems may arise.

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 . 

@hansk46 

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' …...