How to test those NOS tubes

I recently got a VTV tester which lets you listen for noise as well as microphonics. It has been quite an earopener.

Thanks Fletch! In the meantime I've realised this for myself. Throw them into your pre or pre-pre and listen. I've now got a Funke W-19 (Similar to the famous Hickock Cardmatic) where I can match tubes as closely as possible before testing them in the cicuit, where they are to perform. You live and learn. Cheers,

As far as testing tubes, for noise, a George Kaye Noise tester, is the solution. It lets you hear, the actual noise, a tube makes. Most testers, are not reliable, in their noise testing. A better solution, is to match them, with the tester, and then listen to them, in circuit. No tester, can predict, how a tube will act, in every circuit. A tube can be fine, in one amp, and present problems, in another.

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

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..

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

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.

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.

Detlof; As you might surmise from my previous confession, I'm no help at all. I'm still learning. But every thing I posted regarding output tubes is an actual experience. My education has a ways to go--in all areas. I'm not sure if this "tests well- won't bias" carries over to the pre amp or driver tubes. Where are the guys with the *big brains*?

Wow, what a story, George. Luckily I don't have to bias my power tubes. What I need to measure and match especially are those preamp double triodes and to find those with the least noise.

Detlof:...I have near your knowledge / maybe less. My amps are the individual socket biasing type. As in CJ Premere5s.--16 el34s--16 trim pots.

I bought a set of 16 of these nos's--The seller told me these were tested 14 way to sundown. However, 4 wouldn't bias at all.-- In these amps you follow the instructions in the book; baisiclly,insert the tubes,turn all the trim pots back to zero,turn on the amps, turn on the pre no volume. after a few minutes bring the trim pots up till the led glows/ then trim pot goes back, to just extinguish the led. On the 4 that wouldn't bias ; means the led wouldn't go out - at all. I tried the 4 in different sockets/ and the other mono--same result.(Blew 2 fuses in the process)

Ok, A novel to ans your query??--Sorry. My point is that no matter how *these* tubes were tested before I bought them;It didn't matter.--They just wouldn't bias in my amps.No I don't know what gremlins were at work here. A tube tester may not tell you all you want to know-(as in my case)