Anyone Here Ever Purchased A Tube Tester?

@mitch4t Tube testers will not find a sputtering tube. The best way to find it is to swap it with the other channel if that is possible, if not, with another tube of the same type elsewhere in your system.

It can also be a corroded tube socket as previously suggested, but IME your DAC is far too new for that to be an issue. The tube itself is far more likely.

I run dome very old tubes in my system.  Once every three or do years, I get brief sputtering or crackling sounds that then goes away.  I asked the builder about this and he said something inside the tube flaked off and fell onto the heater and the tube will make that noise for a few seconds or minutes until the flake burns up.  He said it is no big deal.  

I frequently blab about everyone who has tube equipment getting an inexpensive tube tester.

I bought this Accurate Model 257 for a friend.

It's results matched the results of my smaller model 157. My Model 157 always matched my big heavy Jackson, so I gave the Jackson to a friend who used to bring his tubes here.

I had one briefly that had three more knobs than the space station cockpit. I sold it to somebody hopefully smarter and more committed than me, which would not have been hard..,