Tubes for my Mac's 275....NOS or just used?

NOS is supposed to mean New Old Stock, new meaning zero hours (brand new).

There are tubes that fit this description but not as many as advertised. Many sold as NOS are in fact used tubes. That being said, used tubes that test new are typically low hours, test equipment pulls or test spares. Many of my tubes are used and bought at great prices.

If you want NOS and willing to pay top dollar, Andy Bauman at Vintage can supply them, just be prepared for a long wait. He is meticulous.

As for Ebay, a good many of my hundreds of tubes came from Ebay and generally I've been treated well. Unfortunately you have to know tubes before you can shop Ebay successfully as there are about 20 levels of quality there every day.

I just bought 4 new Telefunken 12AX7's at Ebay for $164.00. That's $41.00 apiece. I've seen current production 12AX7's for that much.

I've had very good luck with Ebay, look closely at product description and seller feedback.

My advice is seek out a seller that has a reputation for selling tubes with lots of positive feedback.

Be sure specifications are included in seller description such as test results and remaining life and maybe a money back guarantee offer?

Photo's should be in ad, showing general condition, markings, condition of pins and the embossed "Diamond" on the base, surrounded by the 9 pins.

Small signal genuine Telefunken tubes will have this embossed diamond. If not, it was built by another (NOS) producer and sold to Telefunken (rare but possible) or counterfeit.

Counterfeit is unlikely with the best tube sellers, these guys know the difference between tubes, some even read the manufacturer codes and include date and location of construction in the description.

I have almost zero problems with buying tubes like this, the only exception is VERY sensitive locations such as the first gain stage of a phono. This is an especially vulnerable spot as signal from this point on is magnified thousands of times by the time it reaches the speakers.