how do i match up some pairs of loose power tubes?

[skywriter900]

when they retubed my showman last week he put a set ofgroove tubes in,his reasoning was that he couldnt test the loose ones in there...........they werent matched sets..........is there any way i can measure , pair them up and write the values? so that i can have pairs to bias? or should i just pass/fail test them on my emissions tester and stick them on ebay? they are all 6L6 old usa made RCA and Sylvanias, I got ehm in a deal with 3 old fender amps and the tube tester as a package deal.................i think theres about a dozen or so................I know I pulled some out of working amps, that i sold ......to keep for spares..........but im not sure which were which sets...............

[Jim Collins]

One way to do it is to put tubes in an amp. Each time you put tubes in, let them warm up, then turn the amp off standby (so that it is playable). Turn all controls down. Without touching the bias adjustment, measure the bias on each tube. Mark what you read. Do this for all tubes. The tubes that have the closest readings will be best matched.

[FenderFreak]

Tube matching is best done using a proper tube tester that is opperated by someone who know what they are doing otherwise expensive mistakes will happen !!!!

[fezz parka]

For down'n'dirty matching, Jim's advice is spot on...:yay

[skywriter900]

I stopped in an old tv shop 1 day on my lunch and struck up a conversation , guy is a old tube radio collector............he told me to bring in all i got and he would test and mark and help me match for nothing......says he has 2 very expensive testers in the back that dont get much use and he would be happy to help me out........all i gotta do is drop them off........Ya meet some great people in vintage electronics................

[Kap'n]

Tube matching is best done using a proper tube tester that is opperated by someone who know what they are doing otherwise expensive mistakes will happen !!!!

What expensive mistakes can you make matching in the amp?

[fezz parka]

The only one I can think of is electrocuting yourself.:lol

[skywriter900]

could ya take something else out if the tube is bad? maybe a tranny?I think ill let the tv dude test them for me......Play it safe

[Kap'n]

could ya take something else out if the tube is bad? maybe a tranny?I think ill let the tv dude test them for me......Play it safe

Sure could, if the tube is shorted. Not if it's mismatched.

If the tubes are used, aka "pulls," it's a good idea to check them on an emission tester to make sure they're not shorted before trying them in circuit. It's not necessary to use a transconductance tester.

OTOH, if the guy knows some stuff, and is willing to share that info, take him up on it. People who know their way around tube stuff are getting rarer all the time. I've learned a lot of things from my Father-in-law and brother-in-law, who both repaired electronics for a living.

[skywriter900]

some im not sure of.he handed me a whole box of tubes , and a old Accurate Instruments tube tester when i bought the amps.....I stuck 4 in a amp i sold I just switched them around till none were glowing any brighter than the others and gave the guy a handful of spares.......the rest have been in a box in a closet for a few years... Ive run them all on the tester i have but every one came up with flying colors......I should test the brand new ones in the showman just to see if it says any of them are bad.......

[FenderFreak]

What expensive mistakes can you make matching in the amp?

Try blowing the thing to bits, it can happen if the tubes are very different in bias voltage.
However some amps are quite safe to test tubes in like most Mesa due to there design.
But who knows for sure, are you prepared to risk hundreds or even thousands of bucks?
Especially if you can have them tested in a proper tester of nothing.

[Kap'n]

Try blowing the thing to bits, it can happen if the tubes are very different in bias voltage.
However some amps are quite safe to test tubes in like most Mesa due to there design.

Care to elaborate?

Specifically what's going to blow to bits if you set the bias as cold as possible, and bring it up slowly.

That, and what's in a boogie that makes it MAGIC. Is it the fact that you, in can't set the bias as cold as possible, and bring it up slowly, without modification? :lol

[fezz parka]

[skywriter900]

ruroh..............what did i start...........

[FenderFreak]

Tube theory, abridged version.

OK People it works like this.
Bias voltage is only a very small part of the picture, what it's really all about is idle current thru the tube plate.
If the tubes are matched properly then a pair will have about the same plate current and therefore it will work properly.
If the tubes are not matched properly then the plate current will be very different and this is a very bad thing (good if you are a repairer).
So regardless of what you do to the bias voltage if the tubes are mismatched then the VERY HIGH PLATE CURRENT can cause much damage to your expensive amp.
Having the amp on stand by makes little difference because the output transformer acts as a load, this is why the tubes still heat up and glow.

Randell Smith at MESA understands this and so he removed the bias adjustment to stop armatures breaking his amps, in almost all cases a MESA will blow the fuse if there is anything amiss with the tubes, they are designed that way.

So what happens if one tube you are testing has a short?
It either blows the fuse or worse also damages the other tubes, caps and the output transformer.
Now I will add that that is not very common but I have seen a few in my 28 years as an electrical engineer.

If you really want to know the full story study electrical engineering at say a collage for a few years, there you will learn very valuable lessons like the importance of using the correct tool for the job.

An amp is for amplifying electrical signals and a tube tester is for testing tubes.

Now you could try using a screw driver to paint a wall but I don't think you will have much success!

:rofl :rofl :rofl :rofl :rofl

[fezz parka]

Having the amp on stand by makes little difference because the output transformer acts as a load, this is why the tubes still heat up and glow.

The tubes heat up and glow because of the heater current.

Randell Smith at MESA understands this and so he removed the bias adjustment to stop armatures breaking his amps, in almost all cases a MESA will blow the fuse if there is anything amiss with the tubes, they are designed that way.

Smith wants you to buy tubes from him, not from anyone else. FWIW, if there's a short in the tube, any amp will take the fuse. It's not exclusive to the design team at Mesa.:lol

So what happens if one tube you are testing has a short?

As the Kap'n said above, you check 'em in an emission tester when you use pulls. Fresh out of the box tubes won't have this problem.

I've never had an amp blow to smithereens when matching tubes in the amp. Set the bias cold, bring it up, check the current. Works everytime.

PS what an "armature"?":hee