While we're talking 7971's, I have a 4LW clock question

[Terry S]

I have an early Pete Hand 4LW clock using B7971s. Since day 1, tube # 2 has been slightly slow to energize when the IR sensor wakes the clock up. No big deal, I just noticed it, always tube # 2. Maybe a second late at the most. Always figured it was the tube.

Now as of this week, it's tube #3 !!!!! --   Tube #2 lights when it should. WTF??

Pete -- I think you read the group -- any ideas? Just a weird curiosity, nothing else.

Terry

[Kevin A.]

Maybe the high voltage supply is tapped out; just not enough current for all 4 tubes at once. Or the high voltage is a bit low and causing inconsistent ionization across tubes. It could also be a combination of both where the power supply voltage drops when the tubes are brought up, and the last tube to light has to ignite when the voltage is lowest. 

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[Michail Wilson]

Strange, but it could still be the tube.

 

I have a bunch that are slower to trigger / require more power.

 

I also have the 4LW clock which I typically swap tubes in to see how they perform.

Some delay, some flicker.   When I power directly and add more current and/or voltage, they seem fine.

 

Michail

[Kevin A.]

I think the FLW design is also multiplexed as opposed to direct drive. That could very well have something to do with the flickering. Is there any way to tweak the switching frequency of the mux or is it fixed? 

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[Bill Notfaded]

Could you use some jumpers and connect a John Taylor PS up in parallel and see I if that makes any difference? I think that would rule out the power supply? Just a thought.

[petehand]

I suspect it's the tubes. As they get older they take a little longer to ionize when they've been off for a while. Shoot, some that I've bought in Ebay took a day before they would strike. Once they're running, although it is a multiplexed design there are always residual ions in the tube during the dark period, and often for hours afterward, so it should come up instantly after a short break.