Cary Audio SLP-5 Preamp Tube Replacement.

@xcool thanks for your reply. I think I will leave the stock EH in 3 and 6 and only change the four tubes mentioned. I have read somewhere that all tubes interact with each other in the circuit so the sockets has to have tubes in them and not to leave them empty. I might buy tubes for the headphone as I use headphones once in a while. I will try the Psvane once Linlai’s are paid off. 

I have read somewhere that all tubes interact with each other in the circuit so the sockets has to have tubes in them

I have read the exact opposite. And although I realize that this discussion applies to the SLP05 preamp, back in late 2017 (which was back when you could actually get tech support via the telephone from Cary) the Cary tech guy suggested that I run my Cary V-12 amp (which uses a total of 12 EL34s) with only two EL34s perside and set each side’s bia at 80 to 100 mA and see how I liked it. I actually did try that and when I ran it in that configuration I covered the empty sockets with electrical tape to keep dust and foreign objects out. (At the time I didn’t feel it was enough power . . . but I might give it another try as my tastes have changed).

But as far as the SLP05, as far as the balanced input sockets, if you are not hooking interconnects in to the balanced inputs, I truly cannot see how those sockets would interact with the + and - phase buffers. And since I have read nothing at all about leaving the two headphone amp sockets empty if not using headphones, I will not comment on those.

However, with all that typed, IF I was running my equipment into my SLP05 with RCAs, I would still leave the cheap tubes in the balanced input sockets, and in my SLP05 I am NOT (yet) running headphones (although that may change) and I still have the stock EHs in those sockets.

I run Raytheon VT231’s in the gain stages and CBS Hytron 5692 in the buffers fo my SLP05, and they sound glorious. Tubes of this quality are still available from Brent Jessee and others.