? Tube Replacement Question ?

I would check with ARC but I believe it's every 5-6000 hrs. Distortion does go up as the tube ages and sometimes it happens so slowly you don't realize it until you replace them.

Ram Tubes
Jim McShane
Antique Electronic supply

Amperex, or their Bugle Boy is excellent IMO. But, I can't say how they will do in your ARC preamp.

Siemens and Telefunken, for tubes that are known for transparency/freq extension. Mullard and Brimar, for a warmer presentation. Amperex(very popular), Phillips ECG and Sylvania, for a middle sonic ground. All their nine pin, dual triode miniatures, should last about 10k hours(unless run in an unusually demanding circuit).

Thank you for the responses. I noticed that by turning up the preamp volume (without anything playing), there is clearly a "hiss" coming from the right main speaker. The left side is virtually quiet, except for a soft "hum". Can't say that I notice any degradation on sound quality. But that certainly can be due to gradual degradation over the past 4 years (& an estimated 4,000 hours) & my ears have adjusted to it.

I recall a couple of years ago someone on this forum suggested that I talk with Dave Gordon @ Audio Research. I will do that today.