Is tube matching with a tube tester a waste of time?

[tube fanatic]

Some recent research by Daniel Schoo, an expert on curve tracers, has shown that single point matching of transconductance in a tube tester does not in any way predict how the tubes will behave over their entire range of grid and plate voltages. This may explain the higher than expected distortion in push-pull amps when using "matched" tubes, even when they are correctly biased. Definitely interesting food for thought. Makes me glad that I'm currently only doing single ended designs!

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDUQFjAB&url=http%3A%2F%2Fxa.yimg.com%2Fkq%2Fgroups%2F2191247%2F2021419648%2Fname%2FTesting%2520Vacuum%2520Tubes%2520with%2520a%2520Tek%2520Model%2520576%2520Semiconductor&ei=0Kt6UpGpOem_sQTk24CQBg&usg=AFQjCNE7elY9go6r8SCBmVM5tH-7lx-q0Q&bvm=bv.55980276,d.cWc

[Islander]

Some of the old tube testers you used to find in drug stores had the reputation of being extra conservative in their readings, so you'd be more likely to buy some of the replacement tubes that were right there inside the tester's showcase for your shopping convenience.

[mike stehr]

I've been led to believe that the best way to test a tube is in circuit...use the tube tester as a no-go gauge to check for shorts/leakage. Having a tube flash-over/short in circuit is no fun. I learned the hard way with a handful of "NOS" Mullard EZ-81s.

Since the seller knew they were NOS, (and they were) he didn't bother testing them for shorts. I ended up testing a couple of the rectifiers for heater/cathode shorts in a single-ended 6BQ5 amp. Hit the power switch, FLASH!

After the second one flashed-over, and a couple fuses, I went and found a friend with a tube tester.

[tube fanatic]

No question that in-circuit testing is the way to go if looking at a single operating parameter. It's the method that I personally use. Where the curve tracer has the advantage is showing what the tube will be doing across a wide range of operating parameters which will allow for true matching. As far as shorts/leakage go, the tube tester still can have limitations since it's unlikely that the tube will be tested at the voltages encountered in the equipment. Also, when used in the equipment, the tubes will often run at much higher operating temperatures than in the tester which will stress the insulation of the heater/cathode interface. I've seen many which test ok, only to have them arc, short, and so on in the equipment. It's one of the unfortunate limitations of tubes which is why many audiophiles won't get involved with them.

Maynard

[mike stehr]

Yep.

[sunnysal]

if you are running in PP mode I would say that matching would help sure you had close to optimum wave form reproduction. warm regards, T

[bliss53]

Low signal tubes benefit from matching more than power tubes in my experience.

[Guest " "]

tube matching....hum...why do we do it....well...tubes tend to vary in their current draw even amoung the same production batch....even worse when different manufactures are involved. The current value is called Ip. The of course theres transconductance or Gm. so when we buy a matched pair...what are we getting and what good is it? well matched using Ip is helpful if you have PP circuts with only 1 bais pot. But if you have bias pots per tube...then the only benifet of matched using Ip is getting tubes in a general performance range that your amps like. Like as in being able to operate within the range of the bias pot adjustments. Matched using Gm, is gooder if you past the need to match using Ip because having matched tubes that are Gm equal means you are Pee Peeing the same on both sides and there will be less need to play with your hum pot to attempt to reduce noise. I say attempt because with out the right tools and signal...your PP amp will be Pee Peeing worse if you play with your hum pot by ear.

so yes...got a pair of amps that have 10 or 25 power tubes each...it's great if they can Ip close together....but if you have few output tubes or even are SE, then not sure the effort is worth the gain.