Noisy Right Channel

FWIW I don't feel that usually having 'matched' pairs is all that additive. At least I never used them in my ARC pre. Unless your pre-amp has provision for biasing small tubes I'd just cheap out and buy the Sovteks from the Tube store. If they are not perfect performers just use them until you can get better ones, i,e, a matched pair of them, a pair of matched EH's or some NOS (and very expensive ones) and keep them for spares and use them in an emergency like now.  

I had the same problem after I modified a Marantz Model 7 preamp (following personal guidance from Saul Marantz himself!) and had soft hiss and crackling in the right channel. Turned out I installed a defective coupling Mylar capacitor (Mylar because it was 1976), or else I applied to much heat on the capacitor leads while soldering in place. Problem went away after replacing the capacitor.

Could be a bad capacitor, as well as a failing tube.

Matched pairs is more of a power output tube issue than a preamp concern, though I certainly acknowledge that some are paranoid about this issue at every level. 

I’ve bought tubes from Viva, they may not be the cheapest but they usually have what I need and ship the same day.

Here’s a link to Upscale’s tube FAQs.