My uTracer 3+ is complete and it works perfectly when wired for a triode.
1) The manual states that I should be able to test both triodes of a 12AU7 by connecting the second anode to the screen. When I do this I get nothing, is there something I am missing?
2) When attempting to curve trace I keep getting a compliance error and the triode trace plummets to the bottom of the graph. Should I just set the Compliance at 200ma even though the data sheet stops at 35ma? Do I risk damaging the tube?
3) Some of my triodes measure at 100% plate, 100% transconductance, 100% MU, and 87% emissions on the quick test. The same tube on a Hickok made TV-7 measured above 100%. If the TV-7 mainly just tests transconductance and is practically the gold standard, how worried should I be of the emissions rating? Also, some of my tubes have 56% emissions but otherwise test well.
1) The manual states that I should be able to test both triodes of a 12AU7 by connecting the second anode to the screen. When I do this I get nothing, is there something I am missing?
2) When attempting to curve trace I keep getting a compliance error and the triode trace plummets to the bottom of the graph. Should I just set the Compliance at 200ma even though the data sheet stops at 35ma? Do I risk damaging the tube?
3) Some of my triodes measure at 100% plate, 100% transconductance, 100% MU, and 87% emissions on the quick test. The same tube on a Hickok made TV-7 measured above 100%. If the TV-7 mainly just tests transconductance and is practically the gold standard, how worried should I be of the emissions rating? Also, some of my tubes have 56% emissions but otherwise test well.
But have you connected in parallel the grid to the other section with the first ?
And the cathode to ground?
Walter
So using a jumpering the grids together will allow me to test on a uTracer? Pins 2 & 7 of a 12AU7
What do you mean by cathode to ground? I could always take pin 8 and with a banana jack put it to the ground jack of my bench power supply, but I doubt that's what you mean.
What do you mean by cathode to ground? I could always take pin 8 and with a banana jack put it to the ground jack of my bench power supply, but I doubt that's what you mean.
You should have shared connections for the cathodes and grids, then connect the anode of one triode to the screen circuit, and the other one to the anode circuit.
If you the 'triode quick test' it will both halves at the same time.
If you have a graph where you measure Ia and Is together, and step Va and Vs for a range of grid voltages, then you can curve trace them both and match halves. You might need to fix the Y axis for the two graphs to the same range, there is an option for that.
I think it is also described on Ronald's site.
If you the 'triode quick test' it will both halves at the same time.
If you have a graph where you measure Ia and Is together, and step Va and Vs for a range of grid voltages, then you can curve trace them both and match halves. You might need to fix the Y axis for the two graphs to the same range, there is an option for that.
I think it is also described on Ronald's site.
Thank you. And if you purchased some triodes that test 91% gm and 71% emissions on a uTracer quick test would you be sending them back?
Emission is important for a rectifier, since its forward conduction is at its emission limit, and the higher the emission, the lower the voltage drop. Likewise, power output tubes reach their emission limit at maximum output. Now tell me how often a preamplifier tube operates at its maximum emission (hint: never). Most tubes do not have a specification for emission - it's determined ad hoc by testing a bunch under vague conditions. Different tube testers use different voltage and current, may be connected grid-to-cathode or grid-to-plate. Seldom anywhere near operating conditions. But it measures one point on one V/I curve - transconductance measures the slope between two (other) points. Neither is very much information, but as both change with usage, a relative reading may be helpful. If you asked a tube manufacturer about tolerance on transconductance they'd probably say +/-20% at a specified operating point. If you asked about tolerance on emission, they'd probably just laugh.
So then basically 80-120% transconductance is a good reading from what I understand.
Now wouldn't low emissions be a sign of a heavily used tube though? Or would transconductance be expected to drop off way before then? I have some unused tubes of odd voltages (same tube type though) which test at 90-144% emissions and 106%gm, like the whole lot of them. I assume perhaps I have a good but not NOS as claimed tube if emissions are low and transconductance around 80-90%?
Also, the low emissions tubes have pin discoloration. Is this always a sign of a used tube or did manufacturer's back then do a lot of burn in before the tubes left the factory?
Now wouldn't low emissions be a sign of a heavily used tube though? Or would transconductance be expected to drop off way before then? I have some unused tubes of odd voltages (same tube type though) which test at 90-144% emissions and 106%gm, like the whole lot of them. I assume perhaps I have a good but not NOS as claimed tube if emissions are low and transconductance around 80-90%?
Also, the low emissions tubes have pin discoloration. Is this always a sign of a used tube or did manufacturer's back then do a lot of burn in before the tubes left the factory?
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There is/was no standard for emission for most tubes. The exceptions were for rectifiers and certain power tubes like horizontal output tubes. A 6V6 had no spec for voltage drop vs. current, but you could buy the 7408, which was a 6V6 tested for it. The ones that failed could still meet 6V6 specs.
Hard to say what is "NOS" unless you compare to others of the same maker and vintage. Darkened pins may be from heat/use or storage conditions. Burn-in was never common unless a customer was willing to pay for it. Cathode deposits inside are an obvious sign of use with higher power cathodes, though some Mullard power tubes were extreme - I tell people who ask about the black deposits that they only have a few more years of life left.
Both emission and transconductance will drop with use, I don't know which drops faster. A tube that measures with rated transconductance should give the proper element voltages and amplification - until it doesn't.
Hard to say what is "NOS" unless you compare to others of the same maker and vintage. Darkened pins may be from heat/use or storage conditions. Burn-in was never common unless a customer was willing to pay for it. Cathode deposits inside are an obvious sign of use with higher power cathodes, though some Mullard power tubes were extreme - I tell people who ask about the black deposits that they only have a few more years of life left.
Both emission and transconductance will drop with use, I don't know which drops faster. A tube that measures with rated transconductance should give the proper element voltages and amplification - until it doesn't.
91% is within 10% of nominal and pretty much unremarkable but I might take issue with the 71% depending on how it gets weighed against what it is, what you were told you were getting, what it cost and how much it will end up costing to get a replacement in exchange.
Some data sheets give maximums and minimums for the various parameters and some will also give figures indicating "End of Life". Those numbers depend on who made the tubes. Tung-Sol gives a range of 6.5 to 14.5mA where 10.5mA is nominal. If your 71% tube is a Tung-Sol , you're a winner.
Siemens says 8.7 to 12.3 under the same nominal conditions and 7mA indicates end of life. If a Siemens, yours wouldn't meet spec for a new tube.
You might find the perfect triode, with closely matched halves, but it just happens to be microphonic or noisy on one side. The best tube testers have the option of a headset so the tube can be listened to at an operating point.
A tube that is not suitable in one circuit might be fine in another in another role or at another operating point. For example a triode where the halves are quite different but within limits (e.g. 120% vs 70%) is fine as a driver/phase splitter.
There is quite a lot of interesting information about selecting tubes for roles on Lenard Audio ...
My view is that if you have enough candidates then 'every pot has a lid', so they can mostly be matched as pairs or used in some way. To save wastage then buying matched tubes is probably the best solution.
A tube that is not suitable in one circuit might be fine in another in another role or at another operating point. For example a triode where the halves are quite different but within limits (e.g. 120% vs 70%) is fine as a driver/phase splitter.
There is quite a lot of interesting information about selecting tubes for roles on Lenard Audio ...
My view is that if you have enough candidates then 'every pot has a lid', so they can mostly be matched as pairs or used in some way. To save wastage then buying matched tubes is probably the best solution.
12AU7
Cathodes are tied together (pins 3 & 8)
Grids are tied together (pins 2 & 7)
I believe this is what you are telling me to test both triodes at once on the uTracer 3+. Wouldn't this slightly alter the transconductance reading, sacrificing balance and accuracy? Is this considered inconsequential?
Cathodes are tied together (pins 3 & 8)
Grids are tied together (pins 2 & 7)
I believe this is what you are telling me to test both triodes at once on the uTracer 3+. Wouldn't this slightly alter the transconductance reading, sacrificing balance and accuracy? Is this considered inconsequential?
