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Transformers, Coils, Chokes
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31-03-2013, 09:39 PM
(31-03-2013, 11:13 AM)Refugee Wrote: The turns counter started off 30 years ago as the base for a home made frequency counter that never got completed. Then it was a capacitance meter using a constant currant and two voltage sensors that also never got finished... Mmmmm. Nixies  Nixies are always cool Look a bit like ZM1080s or ZM1000s... Just love that cold-cathode/Ne/Ar/Hg look...
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01-04-2013, 12:15 AM
(31-03-2013, 09:39 PM)nickds1 Wrote:(31-03-2013, 11:13 AM)Refugee Wrote: The turns counter started off 30 years ago as the base for a home made frequency counter that never got completed. Then it was a capacitance meter using a constant currant and two voltage sensors that also never got finished... Oops they are not. It all had to come to bits because one of the tubes was duff and it took two chips with it. I have no idea why it had gone bad as it had been dry stored for 30 years with no other ill effects. The count was all locked up until I had replaced the two chips. With no need for a 6 figure turns count i have not bothered to replace the faulty tube. I would have had to buy one.
01-04-2013, 02:43 AM
GNP-7 or GNP-7As then? If so I could sort a spare. Nixies often have trouble lighting up on their standard voltages the first time they are used after a long time unlit... whacking up the voltage briefly can help...
Which drivers? 7441/74141/DM5xxx/etc. or 8xxx series etc. ? Have spares for those too... Its very unusual for the tube itself to go - they have a very long MTBF. Anyway, for a turns counter it really doesn't matter too much
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01-04-2013, 11:07 AM
I do have spare chips for it and they are fixed anyway as it was the right hand side digit that failed.
The decimal point is not connected so the point position is not an issue as i have looked at the data sheet and checked this out. It would not matter if a replacement was GNP-7 or GNP-7A for this task. I have saved the old tube. The sections only partially illuminate. Have you reactivated any from this state or do you have a web link? The existing tubes are GNP-7.
01-04-2013, 11:20 AM
(01-04-2013, 11:07 AM)Refugee Wrote: I do have spare chips for it and they are fixed anyway as it was the right hand side digit that failed.The "A" suffix just denotes no coating so mechanically the GNP-7 & -7A are identical except for the red filter... From the photo it looks like the left-hand side digit is missing... this would be the slowest-moving. Nixies suffer from "cathode poisoning" which sounds like what you have - in answer to your question about tube revival - "yes - many times"! I could explain it here, but there are many pages out there about this and how to get round it, e.g. http://www.tube-tester.com/sites/nixie/d...soning.htm Basically, normally your tube needs about 1.5mA/digit (except for the dps, which need about 0.1mA). To burn off the cathode poisoning, you need to up the current to probably twice that at least, and up the voltage, each digit at a time, until it strikes - maybe up to 250VDC. Run the tube at twice normal current for a while until the digit comes back, then move onto the next one - it may take 10 minutes or more for a digit to fully light again. The tube will get warm to the touch whilst this is going on (do the sums!). Its rare for these tube to fail in normal use - normally they have to be abused in some way, e.g. by long-term overdriving or mechanical damage. Cathode poisoning is the #1 reason for tubes not lighting within spec, but a bit of brute force (see above) will normally bring them back to where you expect them to be. I have many many 1000s of nixies - some of the earlier ones (lab samples) can be a right sod to get going for the first time after storage. Its worth noting that to kick off the ionisation process, a few external photons etc. are normally required - nixies designed to operate in darkness used to have a small amount of Kr85 in them - the β− decay radiation (electrons) got the tubes to trigger reliably. Note that Kr85 half-life is about 11 years, so nixies that originally had a tiny amount of radioactivity are now no longer really radioactive (and were never dangerous to humans in the first place as β− goes only a few mm and are stopped by the glass of the tube)... Consequently, getting nixies to light in total darkness is sometimes tricky.... a bit of cosmic radiation etc. will do the trick.... Cheers
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01-04-2013, 11:51 AM
What i did was to transplant the left hand side tube to the right and replace the 7490 and the 74141 with NOS ones that i had in stock. The original was prefixed FJJ but that was no problem.
I will put the duff one back on my HT supply and see what i can do.
01-04-2013, 12:50 PM
(01-04-2013, 11:51 AM)Refugee Wrote: What i did was to transplant the left hand side tube to the right and replace the 7490 and the 74141 with NOS ones that i had in stock. The original was prefixed FJJ but that was no problem. I believe that "FJJ" was a Valvo prefix for "commercial grade". FJJ 141 is a plain old 7490. In Europe and particularly in Germany they (Siemens and Valvo mainly) used their own chip numbers in the Format Fxx nnn. The 7441 decoder for instance is FJL 101. The 74141 is FLL 101 and the 74142 is FLL 151. The commonly known 7490 decimal counter is FJJ 141 (Valvo, commercial grade) or FLJ 161 (Siemens 0 to 70°C range commercial grade) or FLJ 165 (Siemens -25 to 85°C range extended grade). If you ever find chips with these numbers they are of German origin, often paired with the 74-series code printed as well and often with a 7xxx date code for the manufacturing date, which may add to the confusion rather than give a clue. The year 1974 is still a bad year for reverse engineers who *think* they are dealing with a "7441" marked chip in the middle of a circuit just to find out that this chip only has been made in 41st week of 1974. Cheers
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01-04-2013, 01:13 PM
It took a fair bit of searching in order to get the correct replacements for the chips but it did work first time once they were in. I kept the amount of work on the PCB to a minimum in order to protect it from tracks lifting and so on.
I did write up a restoration post while i was working on it. http://vintagetvandradio.myfreeforum.org...c.php?f=15&t=2892&p=29565&hilit=Micos#p29565 I had to do a fair bit of work on it including making up the sensor. The thread also explains how it stops the motor when the correct number of turns have been wound.
01-04-2013, 01:43 PM
(30-03-2013, 11:56 AM)Skywave Wrote: Winding coils, etc.: another useful book is 'Coil Design and Construction Manual', Bernard's Radio Manuals #160. My copy is quite an old publication and I know that an (updated ?) equivalent was also published by the Babini Press. They are well-written and useful. Yep, a good book, here is a link: http://archive.org/details/CoilDesignConstructionManual I've got the book on my PC and tried to upload it to the Archives section all I got was the revolving whirlygig, it was still revolving after an hour so I gave up...If anyone wants to have a crack then feel free. Lawrence. |
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