Tronola.com has just published an article covering a new vacuum tube analyzer design. This culminates a seven-year project to produce a tester such as the legendary instrument maker, HP (now Keysight), might have built. Full documentation is provided but could a hobbyist build it? Mostly analog, with no uC and no SMDs (except for a small kludge).
Vacuum Tube Analyzer page1
Comments are welcome!
Happy Holidays,
Steve Lafferty
Tronola DIY Electronic Projects and More
PS: Power has been out here and I see that rmyauck already posted a mention of the article--thanks! However, I did still want to post this "official" announcement.
Vacuum Tube Analyzer page1
Comments are welcome!
Happy Holidays,
Steve Lafferty
Tronola DIY Electronic Projects and More
PS: Power has been out here and I see that rmyauck already posted a mention of the article--thanks! However, I did still want to post this "official" announcement.
Simple is a relative term. A Cessna C-150 would be considered simple to fly compared to a B-1 bomber, however, other than both being “airplanes”, they have little in common as each was designed for a completely different purpose.
The same comparison can be made for tube testers. The original purpose, and historically the most common use of tube testers was simply to determine whether or not a particular tube was suitable for service. The ones that achieved this by testing tubes using the “mutual conductance” method became the most relied upon to accurately determine this suitability. Frankly, they are really amazing machines, being able to test with a reasonably high degree of confidence, everything from diodes, to multi-section, multi-grid tubes, including some specialized tubes such as gas rectifiers.
Steve Lafferty’s VTA is not a “tube tester”. It is a laboratory quality instrument that can determine certain tube characteristics with a degree of accuracy that was probably not previously available. Because it can do this relatively quickly, and can easily test a wide range of tube types with a variety of base configurations, it would probably fall under the general classification of being “simple to use’.
The VTA’s significance however is not its ease of use, but its flexibility and accuracy. The attached spreadsheet shows a comparison of fourteen 6BQ5/7189/EL84, etc. tubes that were evaluated on the VTA. All the tube samples were new, unused, from different manufacturers. These same tubes were tested on the popular TV-7, and Gm was obtained from a Gm conversion chart of the TV-7’s simple meter readings. From the TV-7 booklet chart, this tube can be tested with two different loads and bias settings. Those results are shown in columns “J’ and “K”.
The comparison and correlation (or lack of), of Gm results is interesting.
The same comparison can be made for tube testers. The original purpose, and historically the most common use of tube testers was simply to determine whether or not a particular tube was suitable for service. The ones that achieved this by testing tubes using the “mutual conductance” method became the most relied upon to accurately determine this suitability. Frankly, they are really amazing machines, being able to test with a reasonably high degree of confidence, everything from diodes, to multi-section, multi-grid tubes, including some specialized tubes such as gas rectifiers.
Steve Lafferty’s VTA is not a “tube tester”. It is a laboratory quality instrument that can determine certain tube characteristics with a degree of accuracy that was probably not previously available. Because it can do this relatively quickly, and can easily test a wide range of tube types with a variety of base configurations, it would probably fall under the general classification of being “simple to use’.
The VTA’s significance however is not its ease of use, but its flexibility and accuracy. The attached spreadsheet shows a comparison of fourteen 6BQ5/7189/EL84, etc. tubes that were evaluated on the VTA. All the tube samples were new, unused, from different manufacturers. These same tubes were tested on the popular TV-7, and Gm was obtained from a Gm conversion chart of the TV-7’s simple meter readings. From the TV-7 booklet chart, this tube can be tested with two different loads and bias settings. Those results are shown in columns “J’ and “K”.
The comparison and correlation (or lack of), of Gm results is interesting.
Attachments
Agree. It has a lot of knobs. Most are basic K=pin7 switching. No brains needed, just follow the pin-out. Of course you set a heater voltage also. While there is no flip-book or roll-chart to guide you through these steps, you should be able to get this far.
Then you pick a G1 and P voltage (maybe a G2), and read the current. I guess you flick a lever to get the reading, so you don't leave the tube at silly voltages while getting set up.
The meters can read different things. Squint the pix, you get an idea.
I didn't get as far as looking for a tranconductance test. Of course Gm can be inferred from sub-Volt changes in Vg1 and the resulting currents. Or leak 0.1V 60Hz to the grid and read AC plate current.
It is, for a large set of sockets (what ARE some of those??) and a wide range of Voltage/Current, a "universal" analyzer. Will be very useful for some people.
For just *testing*, I like a 4-hole Champ Amp. Test points and a speaker. Run a few known-good tubes through to see what the average Vp and Vk are, listen for approximate gain and *hiss*. While Champ is biased for 12AX7, 12AU7 will "work" at different Vp and lower gain-- you can learn what is "normal" for the AU. Etc. And while there are noise meters, actually hearing the crap is the best guide.
Thanks so much for your comments, folks. First, I would like to thank Arthur Grannell for reviewing the article in great detail and providing many valuable suggestions.
Jazbo8 -- You might be right that a classic tester could be a little simpler but the results won't be as good*. I called the VTA simple to use because it doesn't require anything beyond the basics of what it takes to make its VTA measurements: pin switches; heater, grid, plate and screen voltages; power and TEST switches. All measurements are on the two meter function switches: Meter1 reads all DC voltages and the Meter2 reads results -- that's all DC currents plus Gm and Gp. Okay, I duplicated plate current on Meter1 for convenience and added two toggles for Gm Cal Check and pentode-as-triode but you can leave those in "Norm" position. I don't think it could be simpler without losing a basic measurement.
ArtG -- Excellent -- thank you for posting!
PRR -- I appreciate your insightful comments. The transconductance test is on the Meter2 function switch. You're quite right that testing a tube in the circuit is one of the best ways, especially if you can listen to it! While there isn't a roll chart, a preliminary settings chart is provided in the docs section. More can be added with the data from a tube data book. The sockets provided are: [The comments are a bit whimsical.]
Jazbo8 -- You might be right that a classic tester could be a little simpler but the results won't be as good*. I called the VTA simple to use because it doesn't require anything beyond the basics of what it takes to make its VTA measurements: pin switches; heater, grid, plate and screen voltages; power and TEST switches. All measurements are on the two meter function switches: Meter1 reads all DC voltages and the Meter2 reads results -- that's all DC currents plus Gm and Gp. Okay, I duplicated plate current on Meter1 for convenience and added two toggles for Gm Cal Check and pentode-as-triode but you can leave those in "Norm" position. I don't think it could be simpler without losing a basic measurement.
ArtG -- Excellent -- thank you for posting!
PRR -- I appreciate your insightful comments. The transconductance test is on the Meter2 function switch. You're quite right that testing a tube in the circuit is one of the best ways, especially if you can listen to it! While there isn't a roll chart, a preliminary settings chart is provided in the docs section. More can be added with the data from a tube data book. The sockets provided are: [The comments are a bit whimsical.]
- 8 pin octal, 9 pin mini, 7 pin mini, 8 pin loctal
- 5 and 7 pin nuvistors -- gotta take care of my Fisher FM-200B!
- 8 pin subminiature -- portable radio, anyone?
- 12 pin compactron and 9 pin novar -- my Eico MX-99 FM stereo adapter uses one
- 4, 5, 6 and 7 pin UX -- 4-pin for 300B and the 83 in Hickok testers, 5-pin for 807 in my Fluke power supply
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