Buying tubes on Ebay could be a lot of fun, but at the same time is very complicated and very frustrating (based on the personal experience), because you never know if the tubes you are going to get are going to work or last beyond a week or a month.
There are steps that you can take to avoid fraud and enjoy the newly acquired treasures for a long time:
This one goes without saying – check feedback!!! If you see that there are complains, the price is irrelevant – you will be toughing away your money.
Make sure that the seller allows returns – a lot of sellers don’t take returns on tubes, which doesn’t make sense. All the risk is then on you. Ebay has an idiotic policy that it doesn’t evaluate “subjective” statements like “Strong” or “Weak”, so the seller can claim the tube to be strong, but you get a weak tube and good luck to you if there is not return policy. You are stuck with a fantastic and very expensive piece of junk.
Buy from a reputable dealer – get your tubes from a reputable dealer that specializes in tubes. Yes the price is a bit higher, but the tubes that you buy would last 2-3x longer.
Check test results!!! – no test results, no purchase. Don’t buy tubes that just state that they test good – that’s garbage. If seller tested a tube and states so, there must be test results listed. It gets very complicated here since different testers how different test results. Try to get tubes from a seller that has transcondactance tester – usually stated in millimho, micromho or gm. Emission tester is just no good – I have a lot of tubes that test 95% on emission and are practically dead. Look for names like Hickok, B&K, TV, Western Electric.
I was always very skeptical about selected tubes. I mean, how much different could it be from the non selected tube from a reputable manufacturer (we are not talking about Chinese tubes here). I got 4 Telefunken 12ax7 Selected Tubes when I purchased my McIntosh 275. I plugged then in, and they sounded very nice. Then I looked up the price of the tubes and they were going for $225 each!!! “This is crazy” I thought. How can a tube cost so much compared to the non-selected version that you can buy for ~$40 on a good day. Given that these were NOS and everything, but come on. So I put them away. Later on I decided to sell them – $900 is a lot of money for 4 small tubes.
Tube rolling with MC could be a lot of fun and could lead to a sound that you will not only like, but love. The flexibility is just incredible. This post will focus only on preamp tubes. Power tubes are out-of-scope 🙂
There are 7 preamp tubes in reissue MC 275, V1 (12ax7) – phase-splitter, V2, V5 (12ax7) – input amplifiers. V3, V6 (12at7) – output tube drivers, V4, V7 (12at7) – Cathode followers.