Hazy tubes, 74141

[StoopKid]

I'm using 6 IN-14's and 6 russian 74141 equivalents. My PCB is already made and when I want a tube to be blank I just throw it an invalid code. But now I'm realizing that this it making them appear hazy instead of off, like all of the digits are firing between one another. This goes away if I turn down my voltage but to make it stop, I have to turn down the voltage low enough so that some of the numbers don't completely light up. Is there anything I can do about this?

[StoopKid]

http://i.imgur.com/iXRL7.jpg
Here's an image of what I'm talking about. To get rid of the haze I have to be below 139v across just the tube. To light up the tube I have to be above 143v across just the tube. The problem seems to follow the tube when I swap it. Should I have something in my circuit to drain this current when the tube isn't on?

[David Forbes]

Unfortunately, you don't have many good choices.

You can keep all digits lit at all times, or make new boards with anode
switches. The former is a lot easier.

Chalk it up to experience.
--
David Forbes, Tucson AZ

[Cobra007]

It sounds a bit funny to me. If you use the russian drivers, they have
100V outputs so that shouldn't be a problem at all assuming you use
something around a 180V-200V power supply.

There is however a difference in russian drivers, some are 74141
equivalent and some are 7441 equivalent (while they are both of type
155ID1). Although they behave the same when driving 0-9, they act
differently from a-f. Change the driver, see if it makes a difference,
replacing it with a normal 74141 should also be fine if your anode
voltage is not too high.

Michel

[John Rehwinkel]

> I'm using 6 IN-14's and 6 russian 74141 equivalents. My PCB is already made and when I want a tube to be blank I just throw it an invalid code. But now I'm realizing that this it making them appear hazy instead of off, like all of the digits are firing between one another. This goes away if I turn down my voltage but to make it stop, I have to turn down the voltage low enough so that some of the numbers don't completely light up. Is there anything I can do about this?

If your numbers don't completely light up, it's probably because you don't have enough current. At lower voltages, you may have to reduce your anode resistors to get complete digit coverage. Try paralleling a high value resistor (maybe 10 times the value of the existing resistor) with the anode resistor of a misbehaving digit and see if you get better coverage. Naturally, a meter and some math can help determine the correct resistor for the lower supply voltage.

- John

[Imbanon]

I had your problem, but I was in luck because mine were still
breadboarded.
Turned out my supply voltage was too high. I had to lower it from 200
to 170 volts, and the problem was solved. I would suggest turning your
tube off via 74141, and then lowering your supply voltage untill the
haze disappears. After that, recalculate your anode resistors and
replace them.
That's what I did, and it worked like a charm.