On 2/4/11 11:09 PM, will wrote:
I got my IN-14s in the mail the other day (Well, three out of four,
one was broken, but m_bulb on ebay very kindly offered to send me two
more tubes. Awesome customer service right there). I've been working
on multiplexing them, and everything works well except for the fact
that I'm experiencing some annoying ghosting. My code basically looks
like this:
Any idea why my tubes would be doing this/ideas to fix it? Thanks!
Will,
I took a look at your schematic diagram. The anode driver has a problem.
There should be a high value resistor (220K ohm) between the collector
of the MPSA42 and the base of the MPSA92. This limits the current
flowing through that 180V drop.
The lack of those resistors may be causing way too much current to flow
from the base-emitter junction of the MPSA92, causing it to have a long
storage time.
Also, you don't need resistors between the MPSA42 emitter and ground.
Please post a photograph or two of your actual circuit as you built it.
Many times a problem becomes obvious when looked at by other eyes.
For what it's worth, I used the circuit shown here in my multiplexed
clocks, and they didn't have any ghosting problems.
http://www.cathodecorner.com/nc620akitman.pdf
I also built them on PC boards, so the capacitance of the cathode
connections was lower than it is for a hand-wired circuit. That's why it
would be good to see your actual construction - there may be things
going on that you aren't aware of, not having 35 years of experience
making mistakes in electronics construction as I have.
--
David Forbes, Tucson AZ
http://www.cathodecorner.com/
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