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Old 29th June 2012, 08:28 AM   #11
12E1 is offline 12E1  United Kingdom
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Hmmm.... I just counted 25 DM160 tubes in my junk box.

Damn! Another distraction form the project currently in hand. Using these as a bar-graph style VU indicator is a cool idea though. I'll have to give it some thought.

(I'm currently playing with some Russian IN-9 / IN-13 linear display tubes. They're fun too.)
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Old 29th June 2012, 09:02 AM   #12
12E1 is offline 12E1  United Kingdom
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To address the OP's question regarding supplies....

The "easy" way is to forget negative supplies - voltages are only relative, anyway. I would look at biasing the filament supply at or near +5 volts. One could even consider a DC filament supply fed from a 5 volt regulator. The filaments would be in parallel connected to the regulator and then a single resistor to ground to drop the remaining 4 volts (at appropriate current). That does put a DC bias along the length of the filament, but with a reasonable HT and grid drive voltage, it will have little visible effect.

If using one of the LM391x range of meter ICs where a low level output is intended to light an indicator, then a simple logic inverter (also powered from the 5 volt rail) could couple each output from the LM391x to the grid of the corresponding indicator tube. The LM391x can also be fed from the same 5 volt supply if it's convenient. Since the outputs on the LM391x chips are open-collector, they would need some weak pull-up resistors to +5v (e.g. 4.7k) to provide a clear high-level signal to the inverters.

The last bit is the HT. For the DM160 this is not that critical. They will light with quite low voltages, but a low current supply in the range 20 - 30 volts would be fine, with a simple current limiting resistor connecting each anode to the HT supply rail. Try something like a 47k for each tube and adjust up or down from there (aiming for around 0.5mA per tube when on).

Hope this helps / makes sense.
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Old 30th June 2012, 11:06 AM   #13
Merlinb is offline Merlinb  United Kingdom
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The DM160 is such a crude indicator that I'm guessing you're only using it for decoration, not for indicating something very precisely. In which case you can just feed the audio straight to the grid with via a cap and grid-leak resistor; that will be enough to get it dance along with the audio without the need for a negative supply (assuming the audio reaches a volt or two in amplitude).

Here's a frequency analyser thing I did for a competition, using DM160s. I used a simple ring-of-two current source for the heaters (which are in series), which is much easier than trying to get an exact voltage. These are not precision devices, so they're dead easy to use if you just want a light show.
DM160 frequency indicator video by merlinblencowe - Photobucket

After I made that video I found that lowering the anode voltage to about 40V gave me a better range between bright and dark, so the voltages you use a far from critical. All that really matters is that you don't let too much current through the heater or you'll burn it out!

Last edited by Merlinb; 30th June 2012 at 11:13 AM.
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