Vintage nixie clock

[Radio_Dave]

Hi,

I've been told this clock was made around 1967 from a published circuit, but that's it.

Can anybody identify where the circuit came from, maybe (hopefully) even have a copy?

Thanks
David

[Dekatron]

Is this the one sold on eBay a few days ago? If not you could try to trace that auction and ask the seller.

To me it looks like a homebuilt design with decade counter boards from RS and some extra logic added.

Do you have problems with it or are you just interrested in the circuit?

[Radio_Dave]

Yes it is the one from ebay. The seller made the clock, from a circuit, in 1967 but that's all he can remember.

I'd like to find a copy of the circuit to help me get it working again.

Regards
David

[Dekatron]

What is working and what is not working? I might be able to help you as I am into Nixies and other cold cathode valves.

[dseymo1]

Didn't the seller say that he had built it as part of a design course? If so, I don't suppose that a published design would have been accepted for such an assignment.

[KeithsTV]

I doubt if it was made in 1967 as the 7490 in picture 2 has a date code from 1971. There was a nixie clock in Practical Electronics in December 1970 but I'm 99.9% certain it's not that one. I have a feeling that there was a similar clock in Practical Wireless in the early 70s but I don't have a copy.

I suspect it would date from 71 -73 as LED displays were becoming available at an affordable price around that time removing the need for high voltage supplies.

If you check the date codes on the ICs that should give a fair idea of the construction date.

The circuit should be fairly simple. A divider driven from a squared up 50Hz signal from the low voltage side of the transformer generates a pulse every minute. This drives the minutes counter set to count from 0 to 59. There'll be an output from the minutes counter which drives the hours counter which will count 0 to 12 or 0 to 23 depending whether its set to 12 or 24 hour mode. There'll also be a means of bypassing the first divider to allow fast setting of the time. The power supply will generate 5v at an amp or so for the TTL and about 200v for the nixies.

The minutes and hours counters, probably all 7490s, drive the nixies via 7441 BCD to nixie drivers.

I can scan the PE Dec 70 circuit as a guide if you wish.

Keith

[Radio_Dave]

Originally Posted by dseymo1

Didn't the seller say that he had built it as part of a design course? If so, I don't suppose that a published design would have been accepted for such an assignment.

We mustn't dwell on the Ebay aspect, as we could get in trouble but you're thinking of the sellers, mechanical, nixie clock (which I also won)

Originally Posted by KeithsTV

If you check the date codes on the ICs that should give a fair idea of the construction date.

Hi Keith, I never knew they had dates, please tell me how to read them. I'm also interested in your PE circuit, so a PM is on its way

Thanks
David

[julie_m]

The date codes are 4-digit numbers giving the year and week of manufacture. An IC date code of, say, 8521 means week 21 of 1985.

[Radio_Dave]

Thanks for that. There's one chip with 745 on it so let's say the clock was made around 1974.

Now for some questions... I recognise most of the IC's apart from BP-00, BP-10 and BP-90. Can anybody tell me what they are and do?

Does anybody know it the bridge rectifier, in the attached photo, is silicon or selenium?

Thanks
David

[Dekatron]

Those ic's that you name might be second source for 7400, 7410 and 7490 which are usually used in these clocks, the last one is a counter and the other are nand gates.

I have included a schematic drawing from the "Texas Instruments designer's Handbook" from the early 70's which shows a simple 12 hour Nixie clock, maybe your clock is based on that design, I hope it will help you to get it running.

[jjl]

Originally Posted by Radio_Dave

Does anybody know it the bridge rectifier, in the attached photo, is silicon or selenium?
David

That would be a silicon rectifier, probably a 10 Amp or so type, a bit meatier than is really required for the current required by your clock.

John

[Radio_Dave]

Thanks for all the replies

Originally Posted by Dekatron

Those ic's that you name might be second source for 7400, 7410 and 7490 which are usually used in these clocks, the last one is a counter and the other are nand gates.

But there's one BP-00, two BP-10's and four BP-90's.

Anyhow, I've attached a photo of it "working". Hopefully replacing the 7441's and checking the capacitors will sort it out?

Thanks
David

[Dekatron]

If the figures do not light up completely they are probably affected by cathode-poisoning, which most Nixie's get sooner or later if they are lit every hour. You can read more about cathode poisoning and how to cure it here: http://www.tube-tester.com/sites/nix...-poisoning.htm

It can also be to low voltage for the Anodes on each nixie which results in too low current for th digits to light up completely.

I'd swap positions on the Nixies to see if they light up in all positions and which numbers can be seen and which are foggy.

Then I'd try each of the RS boards by adding a 5V signal t the links numbered A,B,C and D via a resistor to not burn the outputs of the 7490's driving each 7441, then you can see if the display changes accordingly.

If you can post a picture of the prototype boards, the two beside the RS counters and the one staning on its side it might be possible to discern what they are for.

[KeithsTV]

I suspect the BP-00, BP-10 and BP-90 are from Bi-pak and are the same as the TI 7400, 7410 & 7490.

The 7441 is the nixie decoder driver and was replaced by the 74141 which I believe is an improved version. If you have to replace them use the 74141, it's pin compatible with the 7441.

Keith

[KeithsTV]

Here's the circuit of the PE clock from Dec70. it uses a mixture of 7490 & 7492s in the counter chain. The 7492 is similar to the 7490 but divides by 12 instead of 10. Note that the 7490 & 92 have 2 sections, one divides by 2 and the other divides by 5 or 6.

One other point is that these dividers have their supply pins on pins 10 (gnd) and pin 5 (+5v) rather than the more usual corner pins (7 & 14 for a 14pin DIL)

Keith

[Radio_Dave]

Thanks Keith,

It's definitely not the circuit for my clock but it's very similar. It's nicely drawn which makes it easier for me to see how these things work.

FWIW, the original owner remembers the, seconds counting, LED to be a feature of this circuit. Maybe this will help with finding the original circuit?

Thanks
David

[Dekatron]

Could this be part of the circuit for the RS boards?

http://www.decodesystems.com/rs-nixie-2.gif

[Radio_Dave]

Thanks for that Martin, although I don't think it's the same as my boards. They're really rather simply and just hold a 7490 and 7441 ic together with the anode resistor.

.... Anyhow, changing the 7441's got the clock working, apart from one worn out nixie. Setting the minutes, with the push button, can be a little hit and miss and the LED, which counts the seconds, seems to flash from dim to bright rather than on and off but this may be how it's intended to work?

I'll post some pictures when the cabinet is finished

David

[KeithsTV]

It looks as if the RS board is laid out for the 7475 latch, which would be needed if it was to be used in a frequency counter. The latch is not needed for a clock so it is linked out. The board has markings "Links to bypass 7475 shown dotted"

Keith

[Radio_Dave]

Just in case anybody's interested in seeing it restored and working, I've put a video of it working on my Youtube channel: http://www.youtube.com/watch?v=eKM7RGm7wDs

David