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Vintage threads from the first ten years

Tube Output Ratings

3/18/2000 7:25 PM
Tim C.	Tube Output Ratings Hi All, I have a question relating to the ratings of output tubes. When I order tubes from New Sensor they come with one rating handwritten on the box such as 46 or 75. Would that be the plate current that the tube draws? When ordering tubes from Magic Parts(Ruby), they come with two separate ratings. One is for plate current and the other transconductance. How can these numbers be used to relate them to the specific tone or output that the tube will have? Or is there a way to correlate the relationship at all? Thanks, Tim C.

3/18/2000 7:25 PM

Tim C.

Tube Output Ratings

Hi All,

I have a question relating to the ratings of output tubes.

When I order tubes from New Sensor they come with one rating handwritten on the box such as 46 or 75.

Would that be the plate current that the tube draws?

When ordering tubes from Magic Parts(Ruby), they come with two separate ratings. One is for plate current and the other transconductance.

How can these numbers be used to relate them to the specific tone or output that the tube will have? Or is there a way to correlate the relationship at all?

Thanks,
Tim C.

3/20/2000 4:14 PM
Doc	I assume that the single number is a meter scale reading from a typical tube tester, indicating gm with respect to that particular tester's scale. I'm sure that if you received 6L6 type tubes from NS, that you wouldn't get one tube with a 46 and one with a 75, unless they were checked on two different model tube testers. (The 46 seems to be a reasonable number from a TV7 type tester.) Magic Parts has a superior test rig for testing and matching tubes. It's a full-blown laboratory tube tester on a large rack panel with pots and meters to set and read voltage & current on all the tube electrodes. When they test a 6L6, it's done at realistic circuit voltages (unlike that in a benchtop tester, where the plate voltage might be only 150 vdc). They match the tubes based on both gm and plate current conducted, and they do this for no extra charge. These values are clearly labeled on the carton and the tube base. A nice touch. If you want tubes from NS to be graded and matched, you need to go with what they call platinum matching, and pay about another $2 per tube. Otherwise, you can bet they won't be matched after they've been run a few hours. Knowing that MP matches their tubes at voltages similar to those in your amplifier, and that both gm and plate current are shown, there is a rough correlation in my mind with regard to a tube (using the Groovey rating jargon) being subjectively hard or soft. I figure that the ones listed with higher plate current would be similar to low GT numbers, and the ones with high gm numbers and lower idling current numbers being harder, or having GT numbers higher than 5. This is my reasoning, and I don't have confirmation from MP on this. It would be nice if they could offer some guidelines.

3/20/2000 4:14 PM

Doc

I assume that the single number is a meter scale reading from a typical tube tester, indicating gm with respect to that particular tester's scale. I'm sure that if you received 6L6 type tubes from NS, that you wouldn't get one tube with a 46 and one with a 75, unless they were checked on two different model tube testers. (The 46 seems to be a reasonable number from a TV7 type tester.)

Magic Parts has a superior test rig for testing and matching tubes. It's a full-blown laboratory tube tester on a large rack panel with pots and meters to set and read voltage & current on all the tube electrodes. When they test a 6L6, it's done at realistic circuit voltages (unlike that in a benchtop tester, where the plate voltage might be only 150 vdc). They match the tubes based on both gm and plate current conducted, and they do this for no extra charge. These values are clearly labeled on the carton and the tube base. A nice touch. If you want tubes from NS to be graded and matched, you need to go with what they call platinum matching, and pay about another $2 per tube. Otherwise, you can bet they won't be matched after they've been run a few hours.

Knowing that MP matches their tubes at voltages similar to those in your amplifier, and that both gm and plate current are shown, there is a rough correlation in my mind with regard to a tube (using the Groovey rating jargon) being subjectively hard or soft. I figure that the ones listed with higher plate current would be similar to low GT numbers, and the ones with high gm numbers and lower idling current numbers being harder, or having GT numbers higher than 5. This is my reasoning, and I don't have confirmation from MP on this. It would be nice if they could offer some guidelines.

3/20/2000 7:32 PM
Bruce	For what it's worth, Wayne, I have had situations where a single tube in a matched quad from MP go bad and had them send ONE tube out with the same (or as close as possible) Nr., PC:, and TC: numbers. In all cases it was nearly a perfect match for the other three. In a given test, I've assumed that PC: is plate current and TC: is trans conductance. I forgot what Nr. means. Paul and Ember were telling me the other day that they have changed the way they are testing and matching tubes. According to them, they've dropped the time they spend tube matching and the number of redundant cycle testing they do with virtually no difference in QC. Hmm... I don't know about that yet. I've had way too many "standard matched" New Sensor Power tubes come up as far as 9ma to 12ma off across all four tubes in thre fist 30-45mins. Swapping tubes back and forth, in different combinations across the OT, frequently yields a best case scenario of 4ma or 8ma mismatch. And even at that, one tube of a "matched" quad on one side of the OT might be drawing 28ma while the other is at 32ma. Not real bad, but not as good as I would like for the amount of unchargeable and unnecessary shop time involved for me. I'm pretty much done buying the standard match tubes from NS, based on the ups and downs of it all. Magic Part's pretested matched tubes are a little more, they generally seem to last longer and are closer to what I expect, and IMO, given the same tube manufacturer, at a much better price then Groove Tubes. Oh, and what about the nonsense that NS tries to tell us that their Platinum Matched tubes are burned in for 24 hours each? Sheesh!!...Burned in how? What large company would have time and equipment to do that properly? How much filament current would it take to burn in 50 to 100 EL34s over night! Where do they keep that power supply PT? Sorry, I think it's mostly BS. Bruce

3/20/2000 7:32 PM

Bruce

For what it's worth, Wayne, I have had situations where a single tube in a matched quad from MP go bad and had them send ONE tube out with the same (or as close as possible) Nr., PC:, and TC: numbers.
In all cases it was nearly a perfect match for the other three.
In a given test, I've assumed that PC: is plate current and TC: is trans conductance.
I forgot what Nr. means.

Paul and Ember were telling me the other day that they have changed the way they are testing and matching tubes.
According to them, they've dropped the time they spend tube matching and the number of redundant cycle testing they do with virtually no difference in QC.
Hmm... I don't know about that yet.
I've had way too many "standard matched" New Sensor
Power tubes come up as far as 9ma to 12ma off across all four tubes in thre fist 30-45mins.
Swapping tubes back and forth, in different combinations across the OT, frequently yields a best case scenario of 4ma or 8ma mismatch.
And even at that, one tube of a "matched" quad on one side of the OT might be drawing 28ma while the other is at 32ma.
Not real bad, but not as good as I would like for the amount of unchargeable and unnecessary shop time involved for me.

I'm pretty much done buying the standard match tubes from NS, based on the ups and downs of it all.
Magic Part's pretested matched tubes are a little more, they generally seem to last longer and are closer to what I expect, and IMO, given the same tube manufacturer, at a much better price then Groove Tubes.

Oh, and what about the nonsense that NS tries to tell us that their Platinum Matched tubes are burned in for 24 hours each?
Sheesh!!...Burned in how?
What large company would have time and equipment to do that properly?
How much filament current would it take to burn in 50 to 100 EL34s over night!
Where do they keep that power supply PT?
Sorry, I think it's mostly BS.

Bruce

3/20/2000 7:58 PM

Rick Erickson

quote:
"How much filament current would it take to burn in 50 to 100 EL34s over night!
Where do they keep that power supply PT?
Sorry, I think it's mostly BS."

I have no idea if their claims are true or not,but:
If they ran the filaments in series they could run 19 or 20 tubes on each string @ 120VAC and the current would be the same as for a single tube.
A moderate size isolation transformer could be used but probably wouldn't be necessary.
New Sensor has been a consistantly good supplier to me but a lot of my tube business is done through Mojo or Magic Parts since they are on the Left Coast
and the shipping is more reasonable.

RE

3/20/2000 8:09 PM
Tim C.	Doc, I am glad I asked. I would have wrongly assumed that the higher plate current would have related to a higher(Groovey)number using that analogy. You are indicating that it is just the opposite. Thanks a lot, Tim C.

3/20/2000 8:41 PM

Bruce

quote:
"they could run 19 or 20 tubes on each string @ 120VAC and the current would be the same as for a single tube."

Good point!
I'd still like to see what the 24 hour burn in testing consists of.
Bruce

3/20/2000 11:07 PM
MBSetzer	Check out page 580 and 584 in RDH4. About tube matching: "All valves intended for matching should be operated for at least 50 hours under similar conditions to those under which the valves are intended to be operated in the amplifier." Also check out page 94 about emission testers: "Because of the very high value of the emission current . . . emission test is a damaging test and should be performed as seldom as possible . . . A safe value generally accepted for the duration of the emission test is 3 seconds." Mike

3/20/2000 11:07 PM

MBSetzer

Check out page 580 and 584 in RDH4.

About tube matching:

"All valves intended for matching should be operated for at least 50 hours under similar conditions to those under which the valves are intended to be operated in the amplifier."

Also check out page 94 about emission testers:

"Because of the very high value of the emission current . . . emission test is a damaging test and should be performed as seldom as possible . . . A safe value generally accepted for the duration of the emission test is 3 seconds."

Mike

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