Running my spectrum IN18 at 175 volts

[Trumpeter]

Hello all,

I decided to see what effect turning the voltage from 170 to 175 would have on my fadding digits. I do not have a current rating and have not taken a measurement (partly because I have not had time to break out the soldering iron the last week or so). My hope is this may reverse the cathode poisioning. I observed no change so far. Thoughts? Good/bad idea?

I have a heathkit IP17 on the way and even have a recap kit for it ready. I'll use that to try a more direct approach if this higher voltage idea turns out to be uninspired.

[Jeff Walton]

It's the increased current to the cathodes that drives off the impurities.  Needs to be done outside of your clock with a power supply.  I use 8-10mA on a single cathode. The higher voltage is not what "rejuvenates" the tubes... 

Jeff 

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[Trumpeter]

OK, I guess I thought the increased voltage would also slightly increase current. Go easy I am a rank amateur:)

[gregebert]

If your tubes are socketed (assuming they are, because they re IN-18), it's probably best to run them from a separate supply. If your supply has current-limiting, this is easy: Just set the voltage higher than the ionization voltage of the tube (around 160-180), then increase the current to the desired level. Be careful removing/inserting IN-18's; they have soft pins that are easy to bend and it probably doesn't take much more to break them.

If you dont have current-control on your power supply, add a series resistor. A rough starting value would be about 3K for 10mA, and adjust voltage accordingly. Be sure to monitor the current periodically, because it's possible that as the tube rejuvenates, the current could increase. Also be aware of the power rating of the resistor; 1/4 W will probably fry. You can calculate the required power (P=I^2 * R) easily.

If your tubes cant be removed, boosting the supply voltage by a few volts is unlikely to be enough to get high enough current for depoisoning (around 3x to 4x nominal current). If the driver is current-limited, boosting the supply voltage will have no effect. If there's an anode resistor, you could put another one in-parallel with clip-leads to increase the tube current, but you need to be careful. Make sure you know the values of the resistor in the clock, and the one you are adding in-parallel. Calculate their parallel resistance (R1*R2/(R1+R2) and measure the voltage across it to determine the current.

Personally, I've had very little success trying to recover the few bad nixies I have (all are 5031); my conclusion is they have leaked over the previous 50+ years, so no amount of high-current operation will help.

Best of luck; let us know if you were able to recover your tubes.

[Trumpeter]

The heathkit ip17 has variable voltage and current so I plan to go 170v at 8mah and see what happens. I'm not savvy enough at this point to mess with resistors on the clock.