{"id":38,"date":"2017-02-13T19:57:39","date_gmt":"2017-02-13T19:57:39","guid":{"rendered":"http:\/\/eequalspi.com\/?p=38"},"modified":"2017-02-14T05:21:29","modified_gmt":"2017-02-14T05:21:29","slug":"wherein-the-tubes-go-tink","status":"publish","type":"post","link":"https:\/\/eequalspi.com\/index.php\/2017\/02\/13\/wherein-the-tubes-go-tink\/","title":{"rendered":"Wherein the tubes go ‘tink’"},"content":{"rendered":"

 <\/p>\n

About a month ago, I was watching TV. As usual my IN-13 VU-Meter was dutifully bouncing away with the dialog.<\/p>\n

Out of nowhere, one of the tubes made a “tink” sound and the current control went away — the tube stayed ignited, but the “bar” was stuck at the bottom.<\/p>\n

I noticed that the spacer at the far end of the tube was swinging freely, unlike the other, functional tube. Clearly, something had failed — it appeared that the IN-13’s control cathode had eroded and snapped. Chalking it up to a one-off failure, I dug into my spare nixie box and swapped out the tube.<\/p>\n

About a week later, the second tube exhibited exactly the same behavior! This was not a one off, but an early failure mode of the tubes. While a year and a half of use seems almost acceptable, I had expected much more life out of these tubes. Suffice it to say, the game was afoot.<\/p>\n

My first stop was the best Nixie forum on the internet, Neonixie-l<\/a>. Given the circuit schematic and my description, they were as baffled as I was – these tubes generally last much longer than I had experienced.<\/p>\n

Doing a little analysis of my circuit, the conclusion was that the most current my circuit could drive through the tubes was 10mA, which matched my own measurements. Unfortunately, the datasheet<\/a> translated by tubehobby indicated that the maximum current through the tubes should be about 5mA. More current would shorten the lifespan of thetubes non-linearly, so some investigation was warranted.<\/p>\n

To the bench!<\/p>\n

\"\"<\/p>\n

Figure 1: The setup. Multimeter, Function gen, DC power supply. Not pictured, scope, second function generator with AM input.<\/p>\n

Investigation steps:
\n1. Scope HV line (HV supply is TES 1364<\/a> module)
\n2. Multimeter on 220\u03a9 shunt resistor to get I_control
\n3. Input AC Signal — steady 10kHz, varous levels
\n4. Input AC Modulation signal — 10kHz AM’d 100% depth, 1Hz
\n5. DC Signal Input — remove Microcontroller and input DC to 100k\u03a9 resistor LPF before the voltage follower.<\/p>\n

Results:
\n1. HV Line, no input signal: Mean = 143V, V_pp = 8V
\n2. HV Line, full scale input signal (1.8V PP 10kHz sine wave — to front end): Mean = 143V, Vpp = 9V
\n3. Measure control current full system, using AC signal input:
\nI_shunt, no signal = 1mA (micro is still here, did not scope micro, but I suspect it was putting out a small nonzero PWM value)
\nI_shunt, full scale = 11.5mA
\n4. Measure control current, DC injection to IN-13 driver:<\/p>\n\n\n\n\n\t\n\n\t\n\t\n\t\n\t\n\t\n\t\n\t
Vin (V)<\/th>I_shunt (mA)<\/th>Col. Length (cm)<\/th>\n<\/tr>\n<\/thead>\n
6<\/td>13.9<\/td>11<\/td>\n<\/tr>\n
5<\/td>11.4<\/td>11<\/td>\n<\/tr>\n
4.5<\/td>10.9<\/td>11<\/td>\n<\/tr>\n
4<\/td>9.4<\/td>10<\/td>\n<\/tr>\n
2<\/td>4.9<\/td>5<\/td>\n<\/tr>\n
1<\/td>2.41<\/td>2.5<\/td>\n<\/tr>\n
0<\/td>0.045<\/td>0.5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

I also measured the current through the cathode resistor (220k in series with the non-control cathode to ground):<\/p>\n\n\n\n\n\t\n\n\t\n\t\n\t\n\t
Vin (V)<\/th>I_cath (mA)<\/th>\n<\/tr>\n<\/thead>\n
0<\/td>0.04<\/td>\n<\/tr>\n
0.5<\/td>0.26<\/td>\n<\/tr>\n
2<\/td>0.38<\/td>\n<\/tr>\n
4.5<\/td>0.5<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n

Under normal operation, the tubes will never see more than ~11mA, which is substantially higher than the 5mA expected max current to get the full scale, and these tubes have seen a many of hours of burn in.<\/p>\n

\"\"<\/p>\n

Figure 2: 5mA, should produce full scale.<\/p>\n

\"\"<\/p>\n

Figure 3: 10mA, actually produced full scale.<\/p>\n

Also noteworthy here was that the striking voltage is above the max. Taking a closer look at voltages, the voltage between the anode and the indicating cathode when the tube is at 0 scale is 111V. When I drive it to full scale, it rises to 139V. Reading the aforementioned datasheet correctly, the 0 scale drop across the anode to indicating cathode should be at max 99V – it was out of spec but not grossly so.<\/p>\n

The only thing I could think to do is adjust the HVPS to be drive them at a lower voltage (120V), but my recollection from when I breadboarded this was that they did not strike reliably below about 140V.<\/p>\n

 <\/p>\n

Stay tuned for the realization, the follow up and the fix!<\/p>\n","protected":false},"excerpt":{"rendered":"

  About a month ago, I was watching TV. As usual my IN-13 VU-Meter was dutifully bouncing away with the dialog. Out of nowhere, one of the tubes made a “tink” sound and the current control went away — the tube stayed ignited, but the “bar” was stuck at the bottom. I noticed that the … Continue reading “Wherein the tubes go ‘tink’”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,3],"tags":[],"class_list":["post-38","post","type-post","status-publish","format-standard","hentry","category-in-13-vumeter","category-nixie"],"_links":{"self":[{"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/posts\/38","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/comments?post=38"}],"version-history":[{"count":6,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/posts\/38\/revisions"}],"predecessor-version":[{"id":69,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/posts\/38\/revisions\/69"}],"wp:attachment":[{"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/media?parent=38"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/categories?post=38"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/eequalspi.com\/index.php\/wp-json\/wp\/v2\/tags?post=38"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}