I have a Spectrum and I cobbled together a PIR sensor for it. My thought was, that this is the best way of preserving the tube life. It's obvious, isn't it? Tubes not being on will make them last longer.
However, I made an observation that worries me. The tubes develop a fair bit of heat, and you can hear the thermal expansion/contraction when they are heating up and cooling down. It's quite distubing.
So the question is this: Is frequent tube blanking a good idea for large format tubes? With smaller tubes, I'm pretty convinced that it is a positive strategy to turn the tubes off when not is use, but for large format tubes, the mechanical stress of expansion/contraction has to be more damaging than the electrical stress of glowing, doesn't it?
Is it because the tubes are being driven to hard that they are getting warm? The Spectrum can't do ambient light based dimming, only time based dimming, so, regardless of what is going on in their environment, they are going at it full whack. There is an adjustment for the voltage, but it only varies the voltage by a few volts.
well, at this point I honestly thinking it's just better to light them up and leave them lit for ever. Even scheduled blanking will mean they go through 4 mechanical stress cycles per day, and we know that mechanical stress is the way most tubes die.
I only noticed it, because I heard the tubes clicking, like a hot exhaust cooling down.
I've never heard anyone referring to this. Maybe it's a Spectrum thing, but I doubt it.
My IN-18 experience consists of one clock that I designed and built 7 years ago. It is direct drive (HV5530 chips). My anode resistors are 5K (I think - if you want a solid answer I'll need to open up the clock and check cuz I know I changed them a few times and never updated the drawings). There are no fade type features, but overall brightness can be manually adjusted between 1 & 10. Brightness is controlled by 4KHz PWM driving the blanking pins of the HV5530s. I've had the brightness set to 5 for ages, which represents a 50% PWM duty cycle.
The tubes are barely warm to the touch, and I mean barely. Maybe 2 or 3 degrees over ambient. There is certainly no hot exhaust ticking noise when they are turned off. I do have "day blanking" turned on. On average the tubes are off 12 hours and on 12 hours but I do adjust it occasionally for seasons.
With the exception of one tube that suddenly lost its gas, these tubes have performed flawlessly for 7+ years: nice and bright, no flickering, no heating up, and no signs of cathode poisoning at all (I "spin" for 30 seconds once an hour).
Look into it later when the dust is clearing off the crater.
Last edit: 3 years 9 months ago by Ty_Eeberfest. Reason: Typo, damn it!
I wouldn't be too worried. Like Ty I have an IN-18 tube clock in operation now for more than 7 years. During the first year I used a kit from Claus Urbach which had major flaws and nearly killed my valuable tubes.
I then switched to Dieter Wächter's Blue Dream which became available one year later and had luck that all tubes could be healed from the massive signs of cathode poisening Claus' kit caused.
The Blue Dream is also not without flaws - the power supply voltage is 170V while the IN-18 data sheet recommends no less than 200V because the maximum ignition voltage is 170V. This may become relevant in future when the tubes come to age.
The problem with this power supply is mainly that Dieter decided to drive two neon lamps in series for the colon tubes, and that is causing me headaches because in case of new tubes the ignition voltage is barely reached and after about one to two years the colons start to fail.
The data sheet does not contain information about the maintaining voltage, but with the information I found for other tubes with otherwise comparable parameters it should be around 140..150V.
With the anode resistor used the current should be around 4mA. This makes about 0.6W power when the tube is lit which causes heating of the cathode structure. The tubes in my Blue Dream are also audible when the digits move slightly in the mounting structure which is actually the only audible noise the Blue Dream generates.
This noise is audible during normal operation just when changing digits. So leaving the tubes permanently lit will not help here, it will just shorten the lifetime of the clock.
It might be a Spectrum problem. I'm not imagining it, but I haven't measured the temperature rise over ambient. I'll do it when I get back home. The tubes are quite hot to the touch, and I can exclude that it is some effect of changing displayed digits, because turning the clock off causes the cool down "clicking".
I'll do some proper analysis and report back with some data, rather than just impressions and observations.