Re: Interested in B7971

[gregebert]

Are you designing your own board, or using an existing design ? I recently finished my 7971 PCB design, but I'm in the 'countdown hold' before I send out the board for fabrication while I make design tweaks and other improvements.

Sorry, I dont have any extra tubes. Grrrrr....they are getting expensive and rare.

[Luka C]

I'm actually planning on designing my own PCB for it with exact current limiting for each segment as per datasheet. Did you do the same or did you install just one anode resistor and how important is it to stick to the datasheet in that sense?

[David Forbes]

Luka,

Most Nixie tubes only use one cathode at a time, so a single anode
resistor is sufficient for those types.

The B7971 uses a varying number of cathodes, so an anode resistor will
not result in constant cathode current, as its voltage drop is shared.

Use a resistor per cathode. Lower value resistors for longer cathodes
will result in a more even glow. A 20% variation in cathode current is
probably not noticeable.

On 1/22/2017 4:29 AM, Luka C wrote:
> I'm actually planning on designing my own PCB for it with exact current
> limiting for each segment as per datasheet. Did you do the same or did
> you install just one anode resistor and how important is it to stick to
> the datasheet in that sense?
> Dana nedjelja, 22. siječnja 2017. u 06:13:02 UTC+1, korisnik gregebert
> napisao je:
>

--
David Forbes, Tucson AZ

[gregebert]

Yes, I have specific per-segment current limiting. The circuit is simple (NPN transistor with emitter resistor). I aslo have a current-limiter at the anode.

The problem with the 7971 datasheet numbers is that if you add-up all of the spec-value segment currents for an '8' character it's 40mA. In fact, most displayable characters will exceed to max anode current spec of 21mA. The rarity and high price of these tubes leaves no room for error.

First, I created an excel spreadsheet that sums the current for each displayable character, using datasheet values

Next, I scaled back the datasheet values so that in most cases, the total node current is within spec (21mA)

Then I spent several hours plotting I-V data for all of my 7971 tubes (my new nixie bench supply REALLY helped with this task)

For each tube, I visually determined a satisfactory on-current for each segment.

The last step is to reconcile the individual segment current values with the visually-acceptable segment current, while factoring-in tube-to-tube variations.

I'm still tweaking the segment currents; there still is an anode current limiter (21mA) to handle 3 outlying cases where anode current would exceed ratings without the limiter (*, Q, 8 characters).

Admittedly, this design is probably overkill but I'm not taking any chances with those expensive tubes.

Hera are the spec (top row), and scaled (bottom row) segment currents I'm using. As you can see, it just over half the datasheet value. In general, these currents produce decent illumination, at least with the tubes I have.

6	4	5.5	5	5.5	4	5.5	5	5.5	5	5	6	5	5	6
3.5	2.5	3.0	3.0	3.0	2.5	3.0	3.0	3.0	3.0	3.0	3.5	3.0	3.0	3.5

[chuck richards]

Many years ago I made a 16-tube array using B-7971 tubes.

Made my own driver cards for them, one card per tube.
Each of those cards has a storage buffer capable of
storing the data for its tube. Each card has 15 driver transistors
and 15 cathode resistors.

Then I made up a data storage and scrolling circuit for it.
Made my own character generator from scratch using an eprom.
That eprom takes ascii data and puts it on the address pins,
and then the data at any address lights the appropriate tube
segments to read out the proper character.

If anyone would like any of the particulars of this thing, I'll
be happy to share them. I purchased 32 tubes at that time, they
were 11 bucks each.

Chuck

>>> Dana nedjelja, 22. sijecnja 2017. u 06:13:02 UTC+1, korisnik

>gregebert
>>> napisao je:
>>>
>>
>>
>>--
>>David Forbes, Tucson AZ
>>

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[Clarke Payne]

I still have a few original driver boards for b7971. I could try to post a photo if anyone interested.

[chuck richards]

When I built the (16) driver boards for the B-7971 array,
I used the little 4 inch square cards from Radio Shack which have
the 22/44 edge connector. Built (2) card cages for them. Each cage
holds (8) cards. Used 22/44 female edge connectors with wirewrap
pins.

Chuck




>
>
>---- Original Message ----
>From: clark...@gmail.com
>To: neoni...@googlegroups.com
>Subject: Re: [neonixie-l] Re: Interested in B7971

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[Mich...@aol.com]

Hello,

 

Just as an option in case you didn't find a good deal and you don't want to wait to pick them off of ebay, I will sell for $125 each + shipping.  I have plenty.

 

Michail

 

 

In a message dated 1/21/2017 3:56:24 P.M. Pacific Standard Time, luka.culi...@gmail.com writes:

I'm interested in purchasing B7971 tubes for a project of mine, if anyone is willing to sell some, feel free to send me a PM and we'll see if we can sort something out, thanks!

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[Nicholas Stock]

Come on Chuck, don't rub it in....;-) 11 dollars a piece! I wish!

Going price on the bay is about 100 dollars a tube currently. Sometimes less, sometimes a little more. I've managed to pick some up for about 60 dollars a piece on eBay, and that was a good day, but those days are long gone now.....

Perhaps Dalibor should make these too!!

Cheers,

Nick

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[Jeff Walton]

I paid about $8.95 for two B7971 tubes and the Ultronics display board.   I bought them as surplus from Burnstein-Applebee in 1972.  I only bought (8) at the time for a single clock project.  I wish I had bought and stored more of them.  They seem to be about $80-$100 each on ebay today...  My tubes are living happily in a beautiful MOD-SIX clock.

 

Jeff

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[Clarke Payne]

me too. ultronics board and 2 7971 from BA. still have two complete boards (4 tubes). what are they worth now?

Clarke

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[Mich...@aol.com]

Well, about $350 for the tubes.

The boards aren't worth much at all except for the sockets.  Maybe $10 each (socket).

 

I have about 25 complete boards.  Have caught the wife trying to throw them away several times.  I fear she might succeed some day.

 

Michail

[GastonP]

Ah! Good to know. Does your wife usually takes the trash out of the house in the morning or the night? Just sayin'... :D

[Alic]

There's a lot of 6 on eBay :
http://r.ebay.com/BQENBt

[Luka C]

wow, so many posts here. I was busy working on my bachlor's degree and forgot to check this out, thanks for the answers everyone!

[kitehman]

HA holy crap there selling from my hometown, im outta state or i would go test them