advice on pulling the trigger on tubes

[Cliff Schecht]

You can look at the getter to get a basic idea of tube life/usage in many preamp tubes. 12AX7's and the like should have a clear line between where the getter stops and the glass starts. When that line starts looking less sharp that says that the tube has some usage. Also discoloration of the getter is an obvious sign of usage (extreme discoloration can also be a gassy tube).

For power tubes you have to learn to look for signs of ghosting inside of the glass. This is easier as you get into higher power tubes, but most power tubes with usage will show some sort of telltale signs on the glass envelope.

Bad lettering can of course show usage too but a tube can test great with no lettering. I look for burnt lettering and signs that the tube was handled a lot.

Look at what shape the pins are in also.

[Cliff Schecht]

Another way to save big money buying NOS is to find a reputable seller that sells pulls or used old stock tubes. Expect to pay anywhere from 1/3-1/10th of what the tube would cost NOS so you can buy a bunch more and have many tubes to roll through your amps. Ebay IMO is not the best place for this because bidding tends to quickly drive prices up past the point of savings. But there are still guys out there who make a living selling tubes, many who aren't online (meaning you have to luck out and stumble across them). I have a guys card here that sells me tested good AX7's for $8-12 (depending on brand and condition). Good luck finding those prices on ebait!

Make sure they test every tube of course (IMO this is part of any reputable sellers business).