"Matched" Set of Tubes - What Exactly Does That Me

[JD]

If a vendor sells a "matched" quad of tubes, what does that mean exactly? I've read that matching is done on different criteria for differnt people. I always thought that matched means they draw the same mA bias at idle (+/- 1%? 5%?) Can anyone shed some light on this?

[rockstah]

If a vendor sells a "matched" quad of tubes, what does that mean exactly? I've read that matching is done on different criteria for differnt people. I always thought that matched means they draw the same mA bias at idle (+/- 1%? 5%?) Can anyone shed some light on this?

i think you have it right for the most part - from tube to tube u will run into a tube that draws more or less current then the next - tubes are measured and grouped together as far as that these particular four/two tubes draw the same or similiar enough current that they are a "match"
Mark

[Shredder]

Tubes have also been matched in the past by pairing them with other tubes that share (or within an accepted parameter) a specific microhms reading on a tube tester that tests mutualconductance. This doesn't necessarily mean the tube will have an identical current draw as the other, either.

[Bainzy]

I think what JD is saying is that he understands the principle of matching, but isn't sure how close "matched tubes" should be.

As far as I know there is no standard for calling a set of tubes "matched", but generally "matched pairs" or "matched quads" tend to be in region of 5ma or closer to each other. Depends where you're getting them, a place like Watford Valves would give you them very closely matched, whereas eBay you'd be less likely to get a very closely matched pair/quad of NOS tubes because theres less available to try to match.

[JD]

Both replies are great, thanks. Yes, I've read most guys typically match by current draw, within 5% as stated (closer is better) but I've also read others matching by some other criteria other than current draw. I can't find the link now but I do recall a discussion on another board about this, where some guys claim that matching by current draw is nto the correct way to match tubes. Some say any matching is a waste of time and money. I can tell that the closer the match (current draw) the less hum and static I hear.

[Billy Batz]

The problem with matching by current draw is that how closely matched they are depends on the voltages they use to test them and they also drift after a while. Im sure theres even more problems. Ive never once found a badly matched set to sound worse. Really if anything I think Ive noticed it definitely sounds better. But what you dont want that is truly annoying, is one badly matched tube thats way higher then the rest that forces you to bias the rest really cold or that one too hot. You should be able to bias by ear to waht sounds best but in that kind of situation you have to bias by going as high as possible with that one tube without gretaly reducing its life or redplating it while the other 3 are biased 10mA colder or what have you. Thats an intolerable situation. Its the only time Id chuck a badly matched set.

[JD]

The problem with matching by current draw is that how closely matched they are depends on the voltages they use to test them and they also drift after a while. Im sure theres even more problems. Ive never once found a badly matched set to sound worse. Really if anything I think Ive noticed it definitely sounds better. But what you dont want that is truly annoying, is one badly matched tube thats way higher then the rest that forces you to bias the rest really cold or that one too hot. You should be able to bias by ear to waht sounds best but in that kind of situation you have to bias by going as high as possible with that one tube without gretaly reducing its life or redplating it while the other 3 are biased 10mA colder or what have you. Thats an intolerable situation. Its the only time Id chuck a badly matched set.

I agree, that is the best argument really to match by current draw, so you can bias them and not run one really hot or really cold. I have noticed they drift a bit but in my experience they usually drift somewhat together. You're right, too, about lower voltage matching. When installed and measured at something around 500VDC they can vary much more than stated from the test unit. I always try to set the bias based on the highest draw tube, not to exceed like ~70-75% of max power (W) rating.

What is a typical "burn-in" period? I've also read some guys will play them at like 50% bias for a few hours to settle any drift before adjusting the bias up higher. Is this a good practice or waste of time?

[Billy Batz]

I dont know. Theres lots of things like that that people say but I never do that stuff and I also never have any problems. I usually pop in the tubes when Im gonna have the chassis out for a while anyway so its no problem checking on them. I just bias them up and play for a while or leave it sit, check em again some time later. I dont fuss that much. I just make sure they dont redplate and if they are over teh 70% I rebias them.

[Flames1950]

Hell, I rarely ever even recheck them....pop 'em in, bias and let the chips fall where they may. Haven't gotten burned doing it this way yet! Admittedly I don't usually bias at full 70% of plate dissipation so they can drift up a bit before I've got any worries........

[JD]

Another question...what exactly makes a preamp tube "balanced", as some vendors sell at a premium for PI use? I understand the "gain" of each half is often measured. I also understand the arguments for and against the need for a balanced PI tube.

And can a microphonic tube be used in the PI socket or will this produce squealing like in the preamp gain stage? How about a microphonic tube in the reverb send/recover position?

[Bainzy]

I have a microphonic Valvo ECC83 that is unusable in V1 or V2, but in V3 it works. There's no high pitched squealing, but notes seem to sustain a bit less, noticable mostly when you roll the guitar volume down. If you play on 10 all the time you might not notice it - it took me a week or two to notice it myself.

[Bainzy]

I've noticed installations of power scaling allow you to alter the bias for each individual tube - that seems a great idea. If all amps had that, wouldn't that in theory do away with the need for matching?

[Billy Batz]

Yes and I was commenting aboput the on anopther thread. On PCB amps and amps like Bogner, Soldano and other gusy that arent even that concerned with cost, I dont understand why they dont. At least dual bias. Its such an advantage and I really cant think of any disadvantages. People say you dont want to have them that matched for sonic reasons but it works in reverse. With indivdual bias you can purposely unmatch them to any degree you want.