Why Purchase used tubes?

If you are certain what particular tube(s) you favor in a given application, and you wish to eliminate as much uncertainty as possible, by all means buy NOS. But those sellers you can trust to offer genuine NOS are not cheap by any means. I've gambled on many, many tubes on Ebay and seldom been burned, most are suitable for my preamp's line stage duty. I've been able to sample a dozen 6dj8/6922 flavors via Ebay for what one or two NOS tubes from a primo seller would cost. Phono application, a different story. There, it's cheaper long term to just pay a reliable seller for tested NOS I think. Which brings up the factor of how hard a given bit of kit burns through tubes. A lightly stressed application can be considered differently than a highly stressed one.

My answer applies to all types of tubes, but for the sake of clarity my examples will refer only to Mullard EL34. This is one of the most popular tubes ever made and of all I've ever owned (hundreds), only a handful were purchased new. Many of the Dynaco stereo 70 amps in operation today still have their original Mullard EL34 output tubes on board and working perfectly.

These tubes do eventually wear out but old, conservative tube biasing circuits plus the extreme quality of Mullard leaves many of these EL34's alive and testing 80% or more of brand new.

Most of the Mullard EL34's I own were bought for $55.00 to $75.00 each (in large quantity). New stock in original boxes can go for hundreds of dollars a pair. Many times the price is driven up by a collector or avid tube nut, a person not necessarily buying only for performance reasons.

So, the question comes down to: How many tubes do you require, what are you willing to invest in tubes (considering value of the piece they're going in) and how long do you intend owning this after the investment?

When it came to tubing the EL34's in the power supply of my Aesthetix Io and Callisto, I bought the most premium NOS available to insure maximum possible performance. In my Aesthetix this is justified as I have no intention of switching brands and this equipment cost multiple times my investment in these super premium tubes.

If I bought a used Wolcott Presence stereo amp for the bedroom and wanted great sounding tubes, no way would I shell out for original boxed Mullards. Good used tubes beat the stock to death and at a price I can justify.

I'm looking for a very high quality pair of 6922s for my SET pre. Doing my homework, it seems that the Amperex Pinched Waist D Getter PQ is the Holly Grail. Man, are the nos expensive. $560 was a price I was given for a pair. I really don't know if that is fair. I would love to go NOS. What tube comes in a very close second?

My friend buys really extravagant tubes, used. Telefunken 12AX7 are his favorite pick. He pays a fraction of what people do for NOS. Then, he tests them using a far more elaborate method than most - using an ocilloscope as opposed to a tube tester. He ends up with piles of incredibly good sounding tubes (better than a lot of NOS in actual use), and again, at bargain basement prices.

I like the Siemens 7308 tubes in a phono stage they are very durable. I find that the Amperex 6DJ8 Buglboy tubes sound nice in tube output CD players, and you can find them very cheap on Agon. Good Luck.