How to Test a Zener DiodeThis situation, which involves questions about the zener diode functionality, reinforced my decision that all zener diodes should be tested before being soldered in and placed into service. I have read too many DIY posts and letters in AA/AudioXpress about defective zener, where persons warn about ou-of-spec zener and early failure.
I found a DIY-friendly explanation of how to test zener diodes, including the voltage.
I found a DIY-friendly explanation of how to test zener diodes, including the voltage.
No, you started off by claiming the store was less than helpful and borderline rude. That is not asking for testing procedures.
Unfortunately, you are writing in a forum where most of us have had nothing but right-down incredible experiences with the store!
I live in a nightmare country regarding shipment options and import fees. For example, the store doesn’t even have a viable shipping method to me.
The store and the people close to it have jumped though hoops of fire to allow me to purchase (or simply have) things: sometimes sending full kits just out of their kindness of their heart, others paying for second shipments when the first failed to arrive, and most recently with credit due to a part not up to original specs.
So I find it hard to chew the fact that the store was rude. Maybe it was you that sounded demanding and rude? Because, if approached with modesty and gentleness, the store is nothing but AAA class support, help and openness.
You chose the part you wanted to read. That same post asks for test procedures. I am very glad you had excellent experiences with the store.
I’m starting to understand why they send folks here. I don’t care about your experience. This is my experience. I am not rude by nature. I don’t believe anything is accomplished by being rude. I am; however, to the point.
Also, they were not helpful. Period. What else do you want me to say? They were incredible? They were not.
I’m starting to understand why they send folks here. I don’t care about your experience. This is my experience. I am not rude by nature. I don’t believe anything is accomplished by being rude. I am; however, to the point.
Also, they were not helpful. Period. What else do you want me to say? They were incredible? They were not.
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This is how my response to you on the helpdesk completed:
"That said, it's always possible [it was a manufacturing fault]. Keep in mind (a) this is DIY and we can't take responsibility for other people's soldering/technique/assembly/transport/etc or we'd go broke (b) we always try to do the right thing by our customers.
If after following the technical support provided by others in the thread, you still feel the Nutube was defective, I'm very happy to send you a new one."
I am not sure your vibe here was warranted.
The Nutube is covered by a manufacturer warranty and we're happy to assist you obtaining that from the US distributor. Having helped others with this before (maybe 1 every year so far), I can say it will require going through a debugging process, and possible a physical evaluation of the unit requiring postage and a long wait.
Now that's all a bit of a hassle, so in my reply to you I am actually offering to save you the hassle of trying to obtain the manufacturer warranty, and just send you a new one to save you the hassle because I think that'd be the nice thing to do.
There's a reason why products manufactured for the consumer retail market cost thousands of dollars and can still represent great value for money, when you can DIY something for hundreds - in DIY you're taking all the responsibility for everything that can go wrong.
My offer still stands, and you are also welcome to have us guide you through obtaining a manufacturer warranty, but I'd just take me up on my offer if you feel the Nutube was defective.
If that's the case, just respond to your helpdesk ticket. As mentioned we are non-technical on the helpdesk and only provide order related support and directions towards where to ask qualified people for the right answers to technical support questions.
@deicide67:
You stated in post #6741 that you measured 9.5V at T5. 9.5/475 = 20mA which is at the limit of Korg's spec. If your resistor is slightly below 475 ohms you will exceed the spec.
It seems wrong that you are getting 9.5V unloaded from a circuit with a specified 9.1V zener. 9.1/475 = 19 mA, still above the 17 mA typical recommended by Korg but a cold surge value that will drop as the filament heats up.
Suggest you replace the zener with one that meets spec or up size the current limiting resistors to keep the cold limit to 19mA or less.
You stated in post #6741 that you measured 9.5V at T5. 9.5/475 = 20mA which is at the limit of Korg's spec. If your resistor is slightly below 475 ohms you will exceed the spec.
It seems wrong that you are getting 9.5V unloaded from a circuit with a specified 9.1V zener. 9.1/475 = 19 mA, still above the 17 mA typical recommended by Korg but a cold surge value that will drop as the filament heats up.
Suggest you replace the zener with one that meets spec or up size the current limiting resistors to keep the cold limit to 19mA or less.
This discussion about an early failed Korg tube has got me thinking again. I had been thinking about converting the circuit to a constant current LM317 regulated one, but decided not to when I discovered the very small start up surge to a cold cathode. However, what about the overall circuit? I did some calculations.
Korg app note says
MAX current = 17mA
Korg tube resistance = 41R.
So, how do we create 17mA MAX current in steady-state?
At 9.1V and 17mA, then resistance must be 535R, but B1K resistance is 516R (41R + 475R), thus
At 9.1V the B1K nominal current is 17.64 mA
but since the zener range is +/- 5% then the in-tolerance current range is 16.75 mA ~ 18.52 mA which exceeds the Korg specification.
If resistance is 516R and target current is .017A, then voltage must be 8.77V, not 9.1V.
But considering zener tolerance the voltage becomes 8.77V target, 8.33V ~ 9.2V range, which delivers 16.14 mA ~ 17.83 mA, and that might be satisfactory.
However, if we follow the Korg guidance and want 17.0 mA to be the maximum current and we consider the zener tolerance at +/- 5% then the zener must be 8.77 x .95 = 8.33V but the closest (cheap) value zener is 8.2V which seems a little low. (8.4V is available at $13.00 a pop.)
Best zener for the cathode job IMHO is the 8.7V at 79 cents a pop, producing 16.86 mA nominal and a range of 16.02 mA ~ 17.7 mA. Now, in my mind a simple LM317 plus resistor set to deliver exactly 17 mA to both cathodes in series becomes attractive again.
But what does the lower zener voltage do to the bias circuit? Someone else please address that.
Korg app note says
MAX current = 17mA
Korg tube resistance = 41R.
So, how do we create 17mA MAX current in steady-state?
At 9.1V and 17mA, then resistance must be 535R, but B1K resistance is 516R (41R + 475R), thus
At 9.1V the B1K nominal current is 17.64 mA
but since the zener range is +/- 5% then the in-tolerance current range is 16.75 mA ~ 18.52 mA which exceeds the Korg specification.
If resistance is 516R and target current is .017A, then voltage must be 8.77V, not 9.1V.
But considering zener tolerance the voltage becomes 8.77V target, 8.33V ~ 9.2V range, which delivers 16.14 mA ~ 17.83 mA, and that might be satisfactory.
However, if we follow the Korg guidance and want 17.0 mA to be the maximum current and we consider the zener tolerance at +/- 5% then the zener must be 8.77 x .95 = 8.33V but the closest (cheap) value zener is 8.2V which seems a little low. (8.4V is available at $13.00 a pop.)
Best zener for the cathode job IMHO is the 8.7V at 79 cents a pop, producing 16.86 mA nominal and a range of 16.02 mA ~ 17.7 mA. Now, in my mind a simple LM317 plus resistor set to deliver exactly 17 mA to both cathodes in series becomes attractive again.
But what does the lower zener voltage do to the bias circuit? Someone else please address that.
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There are 3 devices in that circuit -- zener, resistor, cathode. The zener is shared by the other cathode that is working properly, resistors almost never fail unless overheated to disaster, and that leaves the cathode. I don't think there is anything to test save for checking solder joints. After that, it's the tube.
If you're going to test and replace, I would look for a zener that is at the low end -- below 9V, closest to 8.7V.
Actually, if your zener is at 9.4V then it is within spec -- 105% of 9.1V is 9.55V -- but still would benefit tube longevity if it were at the low end.