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Testing a 2-01C Diode
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Still working on the recently-acquired 11036A which isn't working. I've checked the probe wiring and don't see anything amiss. When it powers up, the tube gets hot so the heater is evidently working; however, I get no signals back to the meter.
Since I have another probe (this one uses the EA53), I tried that with the meter and it works fine so the problem has to be somewhere in the probe and I'm beginning to wonder if it isn't the tube but am curious as to how that might be considering the heater works (which, I presume, is the primary failure point with these). Before I go spending money on a rather expensive tube, is there simple way I can test this one out of the probe? If I supply heater voltage (via an auxiliary power supply), can I place the diode across the signal source and expect to see half-wave rectification? If I do this, should precautions be made to limit the current through the tube and, if so, how much current is safe? Unless I'm misreading/misunderstanding the specs, the tube is only rated at 1mA DC which seems quite small but, again, I might be misunderstanding that rating. BTW, I'm supplying the AC signal with an HP 3310B function generator. Thanks, Barry - N4BUQ |
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Well, it is just a diode.
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Take a 9V battery, a resistor as a load, and your DVM, and try the battery this way, and then that way, and if the current isn't there in one direction, but is in the other direction, it is probably good. The specs are available on the web, so you should be able to pick your load resistor to match the typical current as specified in the data sheet. Or, you could put it on a curve tracer... -Chuck n4buq wrote: Still working on the recently-acquired 11036A which isn't working. I've checked the probe wiring and don't see anything amiss. When it powers up, the tube gets hot so the heater is evidently working; however, I get no signals back to the meter. |
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Bob Albert
With my 410B I routinely measure the output of my TL922 through the HF range at something over 200 V rms but the current through the diode is limited by its load.? The input signal is coupled via a 2 pF capacitor I think which is just the tube fixture. It's a half wave rectifier and the meter reads the capacitor charge.? So if you don't change the circuit it should be able to be tested.? But recheck the assembly of the probe from the tip to the tube to make sure there is coupling.? And verify that there is a dc path. Bob
On Saturday, July 27, 2019, 10:37:59 AM PDT, Chuck Harris <cfharris@...> wrote:
Well, it is just a diode. Take a 9V battery, a resistor as a load, and your DVM, and try the battery this way, and then that way, and if the current isn't there in one direction, but is in the other direction, it is probably good. The specs are available on the web, so you should be able to pick your load resistor to match the typical current as specified in the data sheet. Or, you could? put it on a curve tracer... -Chuck n4buq wrote: > Still working on the recently-acquired 11036A which isn't working.? I've checked the probe wiring and don't see anything amiss.? When it powers up, the tube gets hot so the heater is evidently working; however, I get no signals back to the meter. > > Since I have another probe (this one uses the EA53), I tried that with the meter and it works fine so the problem has to be somewhere in the probe and I'm beginning to wonder if it isn't the tube but am curious as to how that might be considering the heater works (which, I presume, is the primary failure point with these). > > Before I go spending money on a rather expensive tube, is there simple way I can test this one out of the probe?? If I supply heater voltage (via an auxiliary power supply), can I place the diode across the signal source and expect to see half-wave rectification?? If I do this, should precautions be made to limit the current through the tube and, if so, how much current is safe?? Unless I'm misreading/misunderstanding the specs, the tube is only rated at 1mA DC which seems quite small but, again, I might be misunderstanding that rating. > > BTW, I'm supplying the AC signal with an HP 3310B function generator. > > Thanks, > Barry - N4BUQ > > > > > |
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That's the way I thought of it. It's just a diode and should act like one if it's good. What gets me is the relatively tiny forward DC current rating. For tube construction, that just seems odd - especially considering it's rated at 1000V.
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Thanks, Barry - N4BUQ ----- Original Message -----
From: "Chuck Harris" <cfharris@...> |
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I've checked the connections a best as I can and I'm not seeing anything wrong with it - albeit that the tip capacitance gets in the way of making a continuity check.
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I have tried testing it in the probe and not getting results, whereas the same test with the EA53 probe (the one that works properly in the meter) does work (e.g. it provides a DC voltage to the tip of the stereo jack when the heater is energized and the signal generator is across the probe tip and ground). Thanks, Barry - N4BUQ ----- Original Message -----
From: "Bob Albert via Groups.Io" <bob91343@...> |
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Well, it is a detector, not a rectifier. A very special
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detector in that it works from about a milivolt through a kilovolt. -Chuck Harris n4buq wrote: That's the way I thought of it. It's just a diode and should act like one if it's good. What gets me is the relatively tiny forward DC current rating. For tube construction, that just seems odd - especially considering it's rated at 1000V. |
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I plan to test it per the suggestions. It is possible, though, that I might have damaged it feeding the 50-ohm terminated output of the 3310B directly to the tube tip as I expect that would have produced more than 1mA unbridled current from the generator. I did that before I read about the 1mA rating.
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This poor probe, though, had multiple problems so the tube might have been bad when I got it. I mentioned that the spring connector was falling out of its slotted socket, but I also discovered that the cable's braid was not connected to the sleeve of the plug so the heater couldn't work. I can't tell if it was that way from the factory or whether someone did that intentionally (and I can't figure why anyone would want to do that). Connecting that let the heater start working but have not successfully gotten a signal through the tube. If the tube still checks bad, then I'll be looking for a replacement tube. Thanks again, Barry - N4BUQ ----- Original Message -----
From: "Chuck Harris" <cfharris@...> |
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My recollection is that all that usually happens to
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such a diode, when you try to get more current from it than it is capable of delivering, is it doesn't deliver the current. The cathode is just too small to deliver the flux of electrons necessary to get more than 1ma of current. -Chuck n4buq wrote: I plan to test it per the suggestions. It is possible, though, that I might have damaged it feeding the 50-ohm terminated output of the 3310B directly to the tube tip as I expect that would have produced more than 1mA unbridled current from the generator. I did that before I read about the 1mA rating. |
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Okay - that makes more sense.
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Thanks, Barry - N4BUQ ----- Original Message -----
From: "Chuck Harris" <cfharris@...> |
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I tried setting up a test for the diode using approximately a 3VDC source (a very weak 9V battery I happened to have on hand) with a 3.3K resistor in series between the anode and cathode (naturally, with the heater connected and sufficiently warmed up). I could not measure any voltage across the resister regardless of the polarity of the source voltage. I also tried it with the DVM in series with the resistor/voltage source and still could not detect anything even close to 1ma.
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Thinking that was more-or-less conclusive of a bad tube, I tried this with a NIB EA53 (adjusting the heater voltage accordingly) and still could not see any significant current flow regardless of the polarity of the source voltage. Unless _both_ tubes are bad (unlikely but I can test the EA53 in the working probe to verify that one), then I think this test setup is somehow invalid (although I don't see how with such a simple setup). I'm not where I can get to my workshop for a while so can't report more findings until I get back there but thought I'd pass this along. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Barry" <n4buq@...> |
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Try testing the probe with a solid state diode, nearly any diode will do. Hook it up across the terminals for the tube with correct polarity. See if it works. If it does the tube is probably bad, if not the problem is something other than the tube. Check your tube testing set up the same way. The 410B is a very simple meter, essentially a DC meter with a series diode rectifier for AC measurements.
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You could also test the meter by putting a low DC voltage across the diode output terminals. Maybe your worn out 9V battery drops to zero with any sort of load, I've found some like that. Try a plain old D cell. On 7/29/2019 9:18 AM, n4buq wrote:
I tried setting up a test for the diode using approximately a 3VDC source (a very weak 9V battery I happened to have on hand) with a 3.3K resistor in series between the anode and cathode (naturally, with the heater connected and sufficiently warmed up). I could not measure any voltage across the resister regardless of the polarity of the source voltage. I also tried it with the DVM in series with the resistor/voltage source and still could not detect anything even close to 1ma. --
Richard Knoppow dickburk@... WB6KBL |
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I had wondered about the battery doing just that and plan to try this with a better source. I was seeing a very brief jump of current and if the battery does indeed drop to nearly nothing under any load, then that might make sense.
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The two 410Bs I have both use an EA53 and the other 11036A uses an EA53. This is the only probe I have that uses the 2-01C. It would be nice if I had another probe to test the 2-01C. I'll try substituting a plain diode for the tube and see what that reveals. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Richard Knoppow" <dickburk@...> |
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Vacuum tube diodes have a space region between the cathode and anode, which limits the current that can flow until the voltage between the two is high enough. See the I-V characteristic curve at the below link.
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<> Notice that the 410 has separate meter scales for the 1V and 3V ranges, and doesn't really get linear until above 3 volts, and doesn't really respond at all below 100 mV. There would be current flow with a 3 volt power supply, but perhaps in the microvolts with a 3.3K resistor. Try testing with a much larger resistor, in the meg-ohms, and with a higher voltage. John On 7/29/2019 9:18 AM, n4buq wrote:
I tried setting up a test for the diode using approximately a 3VDC source (a very weak 9V battery I happened to have on hand) with a 3.3K resistor in series between the anode and cathode (naturally, with the heater connected and sufficiently warmed up). I could not measure any voltage across the resister regardless of the polarity of the source voltage. I also tried it with the DVM in series with the resistor/voltage source and still could not detect anything even close to 1ma. |
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While I wasn't able to get the 2-01C or either of the EA53s to act like a detector/rectifier in my experimental setups, (easy enough to do with an ordinary silicon diode, but not so much with these tubes). I was, however, able to substitute a silicon diode and get the probe to at least give me some readings (although, naturally, not correct) which indicated to me that the probe body and cable are working.
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The more I look at this, the more I'm convinced that someone substituted a 2-01C in a probe that was designed for an EA53. I put the EA53 from my other, working probe into the probe that had the 2-01C in it and that worked. I think the size differences in the 2-01C are not so far out that the EA53-designed probe will still accommodate it (not perfectly, but it can be made to go in the socket). The problem now is that the spring tip on the 2-01C is slightly larger than then anode tip on the EA53 and it fits too loosely. I'm not sure if that's because a tip that was supposed to go on the EA53 was forced on the 2-01C or whether the 2-01C had a slightly different spring tip. Given everything else, I'm thinking that it, too, was forced into service on the 2-01C and, thus, is now stretched out a bit. I think I can retwist that spring for a better fit onto the EA53 but would be interested in knowing whether two different spring tips existed and, if so, if someone knows where a spring tip for an EA53 can be had. Thanks for the listen, Barry - N4BUQ ----- Original Message -----
From: "Barry" <n4buq@...> |
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Well, my idea was just to help isolate the problem and it seems to have worked. It may be that a different kind of diode or a germanium diode may be closer to the tube. One of the issues is that the tubes are square law at low voltages and become linear at higher voltages. That is the reason for more than one scale. At low voltages the detector is nearly square law while at higher voltages, say about five volts or higher, it becomes a peak reader. On some meters, for instance the General Radio 1800A, the scales for AC are the same as for DC above 5 volts. I can't remember what the 410B does despite having looked at one thousands of times.
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The difference in the tip contact may be the whole problem, no contact at all due to the tip being the wrong length or diameter. On 8/2/2019 7:48 PM, n4buq wrote:
While I wasn't able to get the 2-01C or either of the EA53s to act like a detector/rectifier in my experimental setups, (easy enough to do with an ordinary silicon diode, but not so much with these tubes). I was, however, able to substitute a silicon diode and get the probe to at least give me some readings (although, naturally, not correct) which indicated to me that the probe body and cable are working. --
Richard Knoppow dickburk@... WB6KBL |
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