Greg,
I concur that these are fine things to do. I adjsuted my base-emitter resistor
so that it would have about 0.3V across it if the base were disconencted form
the circuit and the driving signal was on.
Also, short wires from the driver to the tubes are helpful to reducing
crosstalk. I made multiplexed clocks with direct PCB traces from tube to tube
under the sockets, and did the timing things you mentioned.
Most importantly, ensure some dead time (~100 usec) between turning off the
anode and switching the cathode driver to the next digit's value. That's where I
ran into trouble.
On 2/24/2015 10:12 AM, gregebert wrote:
Before you start hacking-up your PCB, can you try adjusting the timing of your
anode drivers so there is some 'dead-time', say 50-100usec, after 1 anode is
turned off, and the next one is turned on ? Also, if you can turn off all
cathode drivers during the dead-time, that might help. This will ensure the tube
is no longer ionized, and that should either reduce the unwanted glow or make it
more difficult to re-ionize from leakage. And to be safe, dont turn off the
anode & cathodes at exactly the same time (stagger by ~1usec); otherwise you
could create a di/dt problem from the stray inductance of the wiring.
Now, if that doesn't work, next thing to try is a true base-emitter resistor,
for example, moving the connection of R22 to the other side of R21 (see Terry's
note). I dont think the resistor values are critical as long as they are at
least 100K and they are 1/4 watt (or larger). You dont want them to overheat
P=Vcc^2/R, so with Vcc=160V, R=100K, a 1/4W resistor is at the limit. If your
local Radio Shack store hasn't shut the doors yet, grab some resistors. (I just
got some stuff last night at a 95% discount)
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