Tube rolling McIntosh c2600 preamp?

Real simple if you have stock valves, change them, they are BAD..
I've had 50 years with Mac.. Amperex, Tellies, Good RCA if you can find them. PSVANE is a great new option. The stock valves Mcintosh has used for the last 20 years are just cheap...BIG improvement, if you don't notice an improvement, don't spend a lot of money trying to find it..
YOU may not be able to hear it.. Some can some can't. Depends on your hearing. You don't need to change them all, just the pair in the mains to start (AUX) unless your using the phono section.. Amprex, Tellies, Volvo
PSVANE, Mazda, RCA (be careful with RCAs) some Sylvanias (bright).

BTW I use C8,11,20,22,2500,MX110 on the valve side.. I have  few of their SS models too. Good stuff...

Regards

If you want a little nugget for Mac, don’t use Golden Lyon, for signal valves. Mac used GL to voice MC275, but only their power valves, but never their signal valves. Mac used Tellies, Amprex, (Mulards), RCAs (if you can find BP), Volvo. PSVANE is a GREAT valve, and getting better.  The stocks valves, are ok at best, like JJs. They are probably the better of the bunch, top to bottom, for cheapos.
Like I said, if you can’t hear the difference, don’t waste your money. Some can hear the difference, some can’t.

Swap to Sylvanias, if you can’t hear that difference, you know.  But, you have to be honest with yourself. They should blister your ears, if they don’t in any Mac 1959-2020, there is a hearing issue, with a health Mac. Unless you don’t use a tweeter. 

Regards