? Tube Replacement Question ?

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.

Kit,

If it still sounds good to you other than the hiss in teh one channel, try rearranging the tubes in the sp16 in different orders first before replacing.

SP 16 uses 6 tubes. Tubes age at different rates. Location of the tubes in the sp16 slots help determine resulting background noise levels I found. As tubes age differently, moving a "better" tube into a different location can make a difference and buy you time before you are inclined to replace.

Never base tube purchases on the name brand of the manufacturer.
Only an expert reseller can tell who actually made a tube, or its condition.
Fraud and misunderstandings abound in the NOS business, not to mention
the buying and selling of brand names and the relocation of factories in China and Russia etc.
The reliable reseller earns his fee and stands behind his performance rating.

Mapman,

Thanks for the suggestion. I spoke with Calvin at ARC a few minutes ago. He claims that the useful tube life in the SP16 preamp is 3K - 4K hours. I realize that this is just a rule-of-thumb, but that puts my OEM tubes over the top. Although rearranging the tubes might very well decrease the audible hiss, I am equally concerned about the deterioration of sound quality that I might have become accustomed to over the years. So, I think replacement is in order. Rather than "rolling the dice" with NOS, I will likely order directly from ARC.

BTW, one other question: Is it money well-spent to replace all of the tubes with low-noise types or just replace the input tube with a low-noise (& regular tubes for the others)? I realize that the answer can be quite subjective. But, is any audible benefit worth the extra cost? Thanks you, all.