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TESTER-TV10D/U
While testing some tubes today I ran into a problem testing a couple 7236 tubes (Cetron, Sylvania). I had the tester set for 6AS7 thinking this was the class of the 7236. Both tube read out at 200-300 on the GM meter, unlike the 5000-5800 for other tubes marked 6AS7G (Min 1800).
Not wanting to damage the tubes stopped seeking clarafaction of the tube class or settings.
Any advice is appreciated.
Thanks
Wil
Follow Ups:
More similar to 5998 than 6AS7
George
When matching triodes in a power tube (6AS7 for insistence), what variance between the triode 1 & 2 distinguishes Pass/Fail. Is this a fixed number or percentage of minimum GM? Same when matching tubes as part of a match set?
What is the standard one can expect as well as industry P/F spec?
Thank you
Will
TheTubestore.com "Many of the most commonly used pre-amp tubes (e.g. 12AX7, 12AU7, 12AT7, 6922) actually have two identical sections inside of them. These two sections are technically called triodes and are intended to have equal electrical performance characteristics. It is two tubes in one enclosure..."
I don't know what numbers people or companies use when matching tubes.1% gm and +/- 1ma. idle current (for an output tube) is what I think, but I don't know for sure.
The quote from the tube store is interesting "equal electrical performance characteristics". The made we wonder even more.
Here's what I read on their website, it is also interesting "By using "Matched Sections" tubes the two triode sections inside every pre-amp tube will be identical to each other"
I fine it hard to believe that the "matched tubes" they sell have two triode sections that are truly "identical". It would be nice if they gave a % deviation deemed acceptable. For all we know, 2% or even 5% might meet their definition of "identical".
Edit, I found the answer on their page.
"5. How accurate is your matching?
We match tubes to be within 5% of measured plate current (that is, the tubes won't differ from each other by more than 5%, or 1 milliamp in 20). Despite what many people may say, this is about as accurate as power tubes can be matched. Tubes will always test differently from day to day because of fluctuations in the power supply and "drift" in the tube over time as it ages. When you consider that most electrical components in a modern amplifier are built with a tolerance of 10%, this is more than accurate enough. "
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/11/20
Hello Tre, thanks for taking the time to respond and my apologies for the slow acknowledgment. Apparently I don't have notifications turned on.
Regarding acceptable variances for match tubes it turned out to be very elusive, searching high and low for some guidelines. Lots of people banish around the term "Matched Tubes", but is nearly impossible to find a clear and decisive pass/fail variance guidelines.
That said, the 5% quote you found seems to be a reasonable number. My experience is that solid-state components are generally 5% or 1%, 5% being typically what you find in most audio gear, 1% reserved for the highest quality.
Admittedly, I struggle with electronics, knowing just enough to get by and or embarrass myself. I am not certain how the stated 5% plate current relates to 5% GM (mutual conductance), readout on my TV10D/U. I would like to think that a variance is a variance, but I can't be certain of that.
Another thing I am looking to clarify is how my headphone amplifier (Woo Audio WA3, Single-Ended OTL Amplifier) uses triode 1 & 2 on each of the two 6DJ8 tubes. I'm looking for a schematic. My understanding is that the 6DJ8's are to boost the source signal. For example, is the left side signal, running through the left triode 1, and then doubling back for a 2nd amplification in triode 2? I don't know, and likely showing my ignorance here.
All of that said, I developed a small spreadsheet (and label)to show the variance a number of different ways.
The example photo is the variance of two Amperex Orange Globe tubes date code 8D2 & 8D1.
> Value of each triode half (both tubes, vertical below individual tube)
> Average of triode 1 & 2 (vertical total, each tube) and the variance between both tubes (right bottom).
> Percentage variance between tube triode 1 & 2, tube 8D2 & 8D1 (right hand percentage variance between tubes)
This could be a whole lot of nothing, based on a whole lot of nothing in the absence of my finding any industry variance standards on this subject.
All the best and thank you.
so much for identical though ...
hey Tre', I used to have a double album of John Mayall's [I think it was] 50th birthday jam that featured Dave Mason, Harvey Mandell, Mick Taylor {I'm pretty sure] with Aynsley Dunbar ... several other 'name drop' appearances [Clapton?] but I just can't find it contemporaneously ... do you remember such a thing? it's driving me nuts trying to come up with this
with regards,
I don't know it. I find a lot about John's 70th but nothing about the 50th.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
firstly, my apologies to wdctube for the thread hi-jack
and thanks Tre` ... my search lead there as well
I'm going to reach out to Harvey
wdctube, sorry man, had to ask while it was still on my mind
best regards,
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