Numitron and Minitron driving current and heat generated

[Richard Scales]

I have recently built a clock using FFD21 Numitrons / Minitrons/ The spec sheet says that the segment current should be 15mA +/- 2mA - I have measured it at 14.7mA so that should be fine.

I note that after 10 minutes of operation, the displays are warm to the touch.

Now then, I know these things are essentially light bulbs and work on the exact same principle as my reflow oven but...

I appreciate that  there are glowing elements just below the glass so one might expect it but I wonder how warm they should get.

The spec says operating range up to 70 degrees C and they are nowhere near that warm. 

I just wondered if anyone  had any experience of operating this kind of display and what kind of heat you might expect to be generated?

 - Richard

 

[Benoit Tourret]

Hello Richard,

I don't have any Minitron (yet?) so I had a look to my Numitron tubes.

My IV-9 clock was in the sunlight, I checked 47°C (on  the center of a 0)

I put it in the shadow it goes down to 36°C

my Apollo DA-2000 Numitron is at same temperature 36°C, both in a 26°C environment (up to now...)

the IV-9 is given for -60 / +100°C

the DA-2000 for -50 / +70°C

Regards,

Benoit.

[Richard Scales]

Thank you, I'm away right now but will get some temperature readings when I get back and compare.

 - Richard