Calibration tubes

[morzh]

Short of ebay, what's a decent place to get a calibration tube(s) for a tube tester?
What would be a make-sense price?

Does this make sense?

http://www.ebay.com/itm/CALIBRATION-TUBE...1076wt_922

[RCA Fan]

It seems like a gimmick to me since all tubes age over time and no two are exactly the same. I am aware that some tubes are selected for their properties and called "matched pairs". But it would seem to me that tube tester calibration is something done in the factory by adjusting pots and setting values to predetermined levels.

[TA Forbes]

Understand the concept but the "calibration tube" itself would have to be regularly checked like any other piece of precision equipment.

Additionally, because different tubes have different power/bias requirements, I am not convinced that one "calibration tube" would be accurate for the testing of all tubes. I.E., a 6L6 "calibration tube" might be good for establishing a baseline for other 6L6 tubes that you are testing, but NOT accurate for other tubes.

In my opinion, the best way to ensure your test equipment is accurate is to have it calibrated by a tech shop that has the right equipment to do so.

[morzh]

RCA Fan

I don't think it is about "match pairs".
Any calibration involves a known value one compares the measurement against.
It may be a zener, a resistor and voltage sources, or a tube with a known characteristic in question that was measured on a calibrated equipment.

Of course the real factory calibration is probably not performed with a tube; it is probably done with the precision resistor / voltage setup.

However if a calibration tube is used rarely and does not change much, and it was measured as, say, 2500uMho after letting to warm up, using a standard (from the rollchart or a book) setup, on a calibrated, say, 539, I can fully expect a very similar reading on 600A if I follow the same rollchart, using that same tube.

This is not to say that the rest of the tubes should read the same, The only purpose is to make sure that the tester is reading what the other calibrated one was reading using this same very tube.

For me to calibrate using a factory environment would involve 1) finding such a reputable place, 2) sending the tester to them (not cheap), 3) risking the damage in shipment to and from, and 4) hoping that shipping did not screw up whatever was calibrated. Plus shelling out 150-180 bucks for the calibration itself.

if however the calibrated tube concept works, it comes down to the cost of the tube plus shipping (30 bucks), and all I need is to be reasonably close. I am not required to keep my equipment calibrated, and "good enough" is good enough.

For me it does not sound like a gimmik.

[rocketeer]

What is being sold there are ordinary tubes that the seller claims to have tested to a known value on a calibrated tester. But who calibrated the tester they were tested on and how was it done?

Quote:The 6L6 tube is tested against a known calibrated tube on a calibrated 533 Hickok.

Since you can test a tube and determine a value for the tube but can't actually "calibrate" a tube I'm not sure what that means. I'm skeptical.

Larry

[codefox1]

Over the years, I have seen much discussion on calibration tubes, and yes, there may be a vendor or two who has bogey 6L6 tubes with very accurate specs to tune your machine to the best it could be. Somebody wants $30 for a bogey?, take it, and pass it on.

Still, it is informative to test, say a 6SN7 to see if transductance is pretty close from one section to another, or not, and compare a quad of outputs for obvious shortcomings, but the neterhland of others defies us even after all these decades. And of course, it doesn't always matter at all, if only in increments.

[morzh]

So none of you guys sees any value in owning a calibrated tube?
Or is it more of a question of vendor's credibility?

The tubes in question (on Ebay) have one 6L6 and 12AX7 dual triode (speaking of two sections comparison, though personally I don't see any additional value in that). .

[rocketeer]

I don't but that's just my $.02. As long as the tube tester tells me if the tube is good or bad, that's all I need to know because the real test is how it preforms in the radio/phono/amp/tuner. I've had tubes that tested weak and performed perfectly while at the same time I've had tubes test excellent only to find it didn't work in the radio. 35Z5's are great for that, especially if it's lighting the dial bulb. There are one or two tubes that I have run across that sometimes test excellent but have performance flaws when used in the audio circuit (can't remember the numbers off-hand). In my opinion tube testers are nice to have but of only limited usefullness which is why I would never blow a wad of dough on one. The ultimate test will always be how the tube performs in circuit.

If you have a push-pull audio and you want to match numbers that's fine but really, they only need to match each other, not some magical, mystical "calibration" number in order to be "matched", and again, the proof is in the pudding, how they preform in circuit.

Larry

[codefox1]

Amen, let's push this one aside for a month or two. After all are right handed folks stronger or more articulate on that limb? I'm myself left mouse, and no explanation.

[RCA Fan]

I can see where this debate could go on forever. It all depends on your expectations. Since my occupation is not "radio repair man", I don't even bother with a tube tester as they are big, clunky, expensive, and take up a lot of room. My interest in vintage radio is limited to a few models that I enjoy working with but not to the extent that I have to do a bunch of wood working or cabinet refinishing. Therefore, I keep a few tube sets known to be good. If a radio does not behave to my satisfaction, I rotate tubes using the substitution method until an obviously defective tube is located. After all, these are old radios and I don't expect just out of the showroom perfection.

[morzh]

RCA Fan

>>my occupation is not "radio repair man"....
neither is mine. I am, granted, an EE, but my radio hobby is just that - a hobby, and I enjoy an occasional fixing an old radio if I could find one with a cabinet in a decent enough shape.

And yes, tube schematics are often quite forgiving. Even if a tube ventures in a "bad" region on the English scale you may not necessarily notice it. But in some stages a good tube is more important, and it is easier for me to test a tube rather than buy the whole set for a radio that can easily amount to over a 100 bucks, and then buy the one that is suspicious. 5-6 radios, and the a mid-range tester like mine will pay for itself.

My experience is with transistors mostly (speaking of discretes), not with tubes, and I owned a transistor tester (they are much cheaper than tube testers) and although a well-design stage does not rely heavily on, say, Beta, there is a minimum you want there, and this is where the tester comes handy.
When repairing a transistor amplifier I always relied on a simple ohmmeter, I could always test any transistor with it and say if it is leaky or open or shorted, but I would never dismiss a real transistor tester. No you don't need it always but sometimes you are thankful you have it.
Same with a tube tester.

Same, for that matter, with any instrument. A scope, a counter, a generator, a monkey wrench or a snowblower.

[TA Forbes]

Left mouse here too, but then back in the day I threw/pitched right but hit left. I blame it all on my mother, which is what I do when I have no idea why it is what it is.

Agree with Morzh. Tools are important and personally driven. My favorite tool is the car door that I keep next to my radio repair table. If the room gets too hot, I just roll down the window.

Drum roll... cymbal crash... and...

[morzh]

OK.

Whatever you're gonna think of me, I've bought the toobs.

The bogey and the 12AX7.

Well, the 6L6 tests very close to what's written on it, and close enough to what's in the chart.
The chart says 5000, the tube says 5250 and my tester says 5350.

Not so with 12AX7. Both triodes say 1250 in the chart, it is written 1645/1700 on the tube and I have the tester show close to 2500 on either one.

I checked the filament voltage when the line was adjusted with the tube inserted, and the voltage was right on the money (6.15V for the 6.3 and 12.6V for the 12.7). Just to make sure this is not the culprit.

[morzh]

Here's another question (I think I asked it but cannot find where):

When I use the three scales of the 600A tester, they correspond to the red dots on the English knob.

However, for the first one (dot at 73, "3000") there is space before and after it. So,

Does this mean that both spaces belong to 3000 scale, and then the space after the 6000 dot belongs to 6000, and after 15000 - to 15000, or how does it work?

There are 4 spaces on he dial, but there are 3 scales.

[codefox1]

Like all such devices there are voltage dividers and resistors which have probably crept up in value, not to mention the caps which are probably wierd by now.

I haven't recapped and recarbed my 533 yet because it just performs wonderfly. I do notice current production 6L6GC Chinese ones seem to test a little lower than old ones, but not that much, and sound just fine. These testers strain when given a large current filament like a 5U4 or other hog type. Just have to be patient, let it heat up, adjust line, and have a look. Telling is when there are grave differences between plates on a FW rectifier or between sections of a dual triode for example (had half the filament blown on a 12AX7 and chased my tail for an hour. Once.)

Maybe when I finally admit I'm retired...........