Replacing The Stock EH 6SN7 Tubes For Cary SLP 05

Thanks for all the feedback so far.

Do preamp tubes need to be matched pairs? I keep getting conflicting opinions on this. Cary says yes but many others say only power tubes need matching.

A circuit using a pair of tubes(one per channel), in any stage(gain/splitter/buffer), will have better balance if the tubes are matched. Whether you can discern the difference or not(numerous variables), is another matter. Of course if you have a number of stages, and each has mismatched tubes; the effect would be cumulative.

Thanks Rodman,

Do I stick to the +/- 5% tolerance level in tube strength test levels for tubes that are manufactured around the same period? In other words, if I follow this, can I purchase loose tubes and then match them and adjust for imbalances using the balance controls on the pre?

The reason I'm asking is because many of the listings on eBay are for single tubes or multiple tubes that seem to be "loose". Even a lot of them that are said to be matched pairs have different appearances, date codes, labels, etc. but are said to be electrically matched.

I guess it's unfortunate that tube buying at reasonable prices seem to be a crapshoot.

Most of the 6SN7 family tubes that I've purchased, have been in matched pairs. They are worth the wait and cost. Avoid any, that claim to be matched, but are not the exact same tube(internal appearance). A difference in presentation, between your channels, is almost certain to result. I've bought pairs that were identical in appearance/internal structure, but labeled differently(ie: Sylvania 6SN7W/6SN7A), and had differing date codes, but were perfectly matched in sound and electrical measurement. The 5% figure is a good one. Also, the triode to triode balance should be close, for each tube. Buying loose tubes, from different people would be a crapshoot, given that few tube sellers will have the same tube tester, and if they did; how close would the calibration be between them?

I have no affiliation to Brent Jesse other than as a customer, thought this link to his 6sn7 webpage might give you so insights on various tubes

http://www.audiotubes.com/6sn7.htm