Weston 1240 Nixie Tube Digital Multimeter overhaul

50 years old and still going strong. They don't make em like they used to.

[@youtuuba]

I have now restored three of these 1240 meters. The RTL logic IC's are very robust, and I have not yet found a bad logic chip on these. What often does happen is that the 3.6VDC regulator drifts downwards until the supply to the logic is too low; tweaking the 3.6V trim pot to get 3.6V again is often all it needs.

[@SDsailor7]

you have steady hands! I would be shaking like a leaf trying not to mess it up!

[@dougmcartin3881]

Weston was a good quality manufacturer in it's day. They made high quality analog panel meters as well as test gear. Judging from the 1972 date code on the chips this would have been just prior to the common use of 7 segment LED displays. Weston closed most of it's operations in 1987. The remains of the company was acquired by Ametek in 1989. I'm not sure if they continued making Weston branded products after that.

[@youtuuba]

When that Nixie was acting oddly, a good troubleshooting strategy would be to swap Nixies in their sockets, to see if the problem follows the tube or not

[@er5406]

Used to test, repair, and calibrate geophysical electronics in the 70s. I believe the one I had was 5 or 6 digits. Worked well, also had some old Systron Donners. In our old unit cemetery, we had some of the old motor driven digit displays. Don’t remember the brand.

[@nixietubes]

Dont see many motor driven displays

[@er5406]

@@nixietubes - This was 50 years ago.

[@nixietubes]

@@er5406 yeah I mean with vintage meters, i havent even seen those, mustve been lost to time

[@sjm4306]

That is absolutely beautiful!

[@weerobot]

Wow History..This like Slow TV...Relaxing

[@dell177]

Weston was a top notch instrument maker early on but by the time they got to this stage the brains all fell out and the products were not well made. That said they had lots of company 9n that area. I had a 1916 AC voltmeter that was dead accurate from 50-400 hz and read true rms volts.

[@danmackintosh6325]

Love the hand taped double sided board, the gold pins on some of those chips, how spacious it is to work on & just the general feel of quality that comes across even on video. Ohhh, thing of beauty and a joy forever as Dave Jones would say. Is that a big selenium stack between the two big caps though? Why would they choose that over silicon in something of this vintage?

[@jessede1970]

hello dave hope you have a good week this week nice you found some motors for your tape decks and hows the hot weather and your cats!!!!hope the family are all well!!!

[@_windows_software_wizard_2136]

Man i enjoy your videos

[@chriscutress1702]

Neat to see the old technology. I've got a time code reader (DYNEQUIP Film Timer) that uses Nixie Tubes. I plug it in once in a while for the light show. I don't use it on a regular basis as parts would be impossible to replace.

[@SDsailor7]

Man! you were doing surgeon work there soldering that thin wire on the bulb.

[@hifismiffy]

A nice piece of kit ! Re. your pronunciation of solder, Americans do my head in with Sodder. My real annoyance is anyone who says Technics as Techneeks - that does my head in!!

[@nixietubes]

Techniques?

[@12voltvids]

What is funny is i always pronounced it "tech-nicks" around the Panasonic rep just to piss him off and he would correct me telling me it was "techniques"

[@geirendre]

What's the name of that power connector at the back of that unit? Have seen it on some old HP instruments among others, just never known the what it's called.

[@tekvax01]

Those PH-163 power cords are very difficult to find these days! I have a couple at home for some gear.

[@marka1986]

Typewriters used those as well. I always knew that type of power cord as a businesses machine cord.

[@zx8401ztv]

I would imagine the mode/range switch is a bit mucky, could be the reason it wanders around.

[@BoB4jjjjs]

I would imagine that, it looks gold plated though, still a squirt of cleaner might help. Then again. it might turn black!

[@zx8401ztv]

@@BoB4jjjjs Maybe the rotary one is mucky?

[@BoB4jjjjs]

@@zx8401ztv Could be, but 1K out!

[@zx8401ztv]

Hmm, depends on the reference resistors as well for accuracy. I found the diagram for the 1242 but my posting of the site address vanishes. I dont know if dave has blocked addresses or there is something odd happening. Never mind.

[@BoB4jjjjs]

@@zx8401ztv Sometimes KZbin blocks them, next time it drops one in and you didn't mean to put one in, if you hit # instead by mistake it put something in,

[@williamsquires3070]

I’m more curious to know how they managed to get it to work on 400 Hz, since there appears to only be one step-down transformer (or was that the step-up transformer for the Nixie tubes?) IIRC, 400 Hz is used in avionics. Maybe this unit was marketed for avionics techs? And look at all those ceramic trim caps in there! 😊

[@12voltvids]

Step up and down. Low voltage for the chips. High voltage for the nixie.

[@youtuuba]

I don't think that the power transformer necessarily steps up. The Nixie and neon bulbs on this model run at 90VDC, but that is half wave rectified and unfiltered. Since the circuit is a Villard Doubler, the secondary winding might still be less than 120VAC.

[@youtuuba]

The 400Hz is not that difficult. But I agree that the reason they included 400Hz power in the specifications was to endear themselves to a potential aviation market.

[@maxwarfield6699]

Long shot but, here goes: I have this Lil Leigh 3501A by Nash & Harrison Ltd Ottawa [?] Nixie tube multimeter. It’s in great cosmetic shape but no matter what you try to measure, it only displays 0.800. I’m still quite the novice, so my troubleshooting skills are… not great. This is what I’ve found so far: the fuse is ok. There are no visible signs of burn marks or burn smells. Most resistors checked ok, except for one or two which should have read 10KOhms and instead read a bit lower. Used a light bulb-limiter, no short. Felt the tops of some IC’s [after 10 minutes], the mc7475L 6945’s where warmer then the other chips. If you reverse the test probes, you do get a negative polarity indication, on the display. Nowhere on this device, does it say whether this unit is for only DC or AC measuring. I did notice that the low voltage markers, on the main board, which should all be 15V, all read around 12.84V instead, but on the second board the 5V required, was present. After watching your video here and learning that nixies run on around 170V, I’m kind of scared to push my investigations any further. Got any ideas, please let me know. I want to learn. Thank you kindly

[@12voltvids]

Not familiar with it sorry

[@SDsailor7]

@@12voltvids Would it be worth it to buy one of these multimeters? There is one for sale on one of the auction houses and i am wondering if i should get it. Very interesting how they work, and as always great video! Thank you

[@SDsailor7]

@@12voltvids Did you find a service manual for the DMM?

[@SDsailor7]

@@12voltvids What type of probes does it take? can you use the banana type? it look like you were using banana type.

[@12voltvids]

@@SDsailor7 no

[@danmackintosh6325]

400Hz... Hmm, would that mean it was possibly used as an on-board diagnostic tool in aircraft? (Seem to recall they use 400Hz though could be wrong, mostly am lol)

[@tekvax01]

do those nixie tubes have a left and right decimal point? are they the B-5755's?

[@tekvax01]

I've seen that double-digit display issue with the nixie clock that I designed and built. It was a BCD decoding error due to indeterminate TTL/DTL levels.

[@tekvax01]

There is a nice Burroughs tube application note document for the Fairchild drivers online.

[@Godzilla941]

Thul-durr. :)

[@nixietubes]

Beautiful meter, i can only find a panaplex version :(

[@12voltvids]

Panaplex is cool too.

[@nixietubes]

@@12voltvids not nearly :( Love your vids though

[@12voltvids]

@@nixietubes It's also a neon display. Numitron is also an interesting display. I'd like to find a counter or meter with a nimo display.

[@nixietubes]

@@12voltvids Haha good luck with that my guy, those tubes are high purity 99% unobtanium. I've never even seen a nimo meter. I'd love to see you tear one down but I wouldnt blame you for not touching it. But yeah, numitrons are good too.

[@12voltvids]

@@nixietubes I knew an old ham that had a frequency counter with nimo tubes. Had lots of phosphor burn. Don't know the age of it or even the manufacture. Just remember seeing it all apart on his work bench as it was broken at the time. He died in 1995 so i am sure all his old crap just went to a land fill. That or one of his ham friends scooped it up and parted it out. One of the tubes had "0" badly burned into it as he operated mostly on the low band and the 10mhz tube was usually displaying a 0 or 1.

[@MrRadioGypsy]

Then it is a good thing that you didn't have the same teacher for auto shop classes in HS; because he would have given you a lower grade for saying "Graj'" - instead of "Ga'-rage". Or even Gar-age', as they say in the UK . . .

[@R.AudioElectronics]

You are American and Canadian