How to test those NOS tubes

Detlof: I am pretty sure that special test amps are needed in order to measure noise. Maybe there is a way (with additional equipment) to test them while running in your amp, but this is just a guess? Most testers just measure for GM and MU (think that's it, haven't used one for over 25 years) and may have a feature that will allow you to drop the current down approx. 10% while they are still in test mode in order to see how much the first reading drops. Generally the greater the drop, the less life left in the tube, but there may be exceptions to this. I am far from an expert and just followed the test instrument's instruction manual when I used to test tubes for my guitar amps. I purchased my Hi-fi tubes new (as needed) at this time and never bothered with it, but then again I had never heard of NOS tubes 25 years ago. LOL. Speaking of 300B's (I am a fan of the late production Svetlana's from Conus Audio in Canada) there is talk of a new TJ Meshplate at AA that looks very interesting.

When I purchased my ARC Classic 60 many moons ago I kept the bias data that ARC so graciously supplied. When it was time to retube I purchased the tubes from ARC and requested tubes with the same or as close the data on the origionals. ARC did a great job doing this and it came at a premium but all I need to do was plug them in, burn them in and I was all set. If you kept your data maybe your manufacturer will do the same.

Sorry Detlof. I saw WE and immediately went into 300B babble on the last post.

I'm not a big tube fan myself but I recall reading somewhere that the performance parameters Mr. Detlof wants to measure are available from a "curve tracer" (one made for tubes of course) which sweeps grid voltage & plots graphically vs. plate current. I believe that these tracers are fairly expensive (cost not justifying return on investment unless you're "in the business") and require a fair amount of electronics knowledge just to operate & also to interpret the "results". Idle noise measurements could be made with a test fixture & a wideband AC voltmeter or scope; don't think that the curve tracer does that too..

Thanks Bob bundus, Dekay, I seee I'm steppping into deep water....