B-7971 Array

[Leroy Jones]

Built this in 2001.  Each tube has its own driver card.  Each card contains (2) 74LS273 8-bit latches.   MPSA42 transistors switch each segment via 30k anode resistors.

74LS273 outputs operate transistor base via 100k resistor.  15 of 16 bits used for tube.

There is one extra unused bit.

[Audrey]

Wow. That's amazing.

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[Leroy Jones]

Here's another.

[gregebert]

How much were 7971's selling-for back in 2001, or whenever you got them ?

Today I see them around 200 USD; I paid 80 USD back in 2017 when I built my 8-tube clock.

Long ago, as in the 1970's, I think PolyPaks was selling surplus 2-tube modules for 8 USD.

[J Forbes]

history is hard to find! I think they were on the order of $25 each in the early 2000s. Although the inflation happened pretty regularly.

I was looking at some old posts from 2002, folks were discussing the outrageous price of $800 for a box of 100 ZM-1040 tubes  :)

[Jim KO5V]

That's great! I remember seeing a picture or video that display - or one very much like it.

I bought most of my B-7971 tubes between 2002 and maybe 2005, and I think I paid $20-$30 each. A seller who seemed to have a LOT of them, would put them into the shipping box in their original styrofoam packaging, which had been broken broken up into sections, and then add random broken styrofoam pieces as filler. It was sloppy and lazy, and you could hear things moving around inside of the box. They didn't seem to care because there were plenty of tubes to go around. I received one broken tube, and they replaced it, but I think I had to pay the additional shipping cost.

I think that's about the time I started following this list. It was when Ray was running it.

BTW, I actually received my Geekklock kit from him, but I never got the "Accessory Module". Many people got nothing. His design seemed to be pretty good, and the kit was very nicely done. It must have turned into a pyramid scheme where he was paying the old debts with money from current sales, so eventually there was no capitol to buy parts, and it finally imploded. The situation was very sad.

Several years ago, I started simplifying my life a bit, and I sold some spare tubes that had been gathering dust for years. Then, my MOD 6 clock was involved in a remodeling accident (covered here when I was looking for some replacement tubes). Fortunately, I was able to replace them for just a bit more than my selling price because members of this list took pity on my poor clock!

Jim

[Leroy Jones]

Those B-7971 tubes cost between  $10 and $12 at the time, which was 2000, 2001.   There was an Ebay seller who sent them wrapped in newspaper.

OLD newspaper from 1968, 1970 era!    I bought up a nice stock of them and sockets.   The plan at the time was that since my B-7971 display system

is of modular construction, and since each module is a group of 8 tubes, the initial construction was for (2) of these modules.   I got enough tubes and sockets

to make a 3rd module, so that the readout array would be 24 tubes wide!    But that 3rd module has not yet been made.    Stocked up on enough tubes

to have plenty for a 24 tube array, plus several spares.   In the recent reactivation of this project, this time I did a complete teardown of the scrolling logic.

That logic was on (2) 3220 point solderless boards and it was never very good, it was highly experimental, a prototype just to get things working.

Everything is slowly being tested carefully, piece by piece as it slowly goes back together again.    It is driven from an old ancient Radio Shack ASCII keyboard

kit.    That kit has 19 old old plain 74XX series TTL.  That keyboard draws 300 milliamps just by itself!     Those (32) 74LS273 ICs on the tube driver cards draw

another 500 mA.    I am seriously thinking of changing out those "LS" series chips with 74HC versions.   Much less current.   What do you guys think of that idea?

[gregebert]

Radio Shack ASCII keyboard ?? Is that the one that doesn't have a RETURN key (gotta use CTRL-M), but it does have a linefeed key ? I built a video terminal with that in high school and was thrilled I could use a 300 baud connection.

Switching to 74HC should reduce your power. I recall there was one "oddball" 74XX IC that wasn't sold by RS, and they included it in the keyboard kit.

Glad to hear you have a nice stock of tubes and plan to use them.

[Leroy Jones]

Yes, that's the one!   Radio Shack catalog number 277-117.   The IC included in the kit was 74H103.  Mine came already assembled when it showed up in a box

full of parts I rescued from the local tech school when they closed up.   It is in rough shape.   The builder decided to solder in sockets for the ICs.   They are all those real

crappy old sockets.   This keyboard woke up flakey as hell after being dormant since 2015.   Took me a few hours of testing and trouble shooting to get it working again.

Not quite sure why they used the 74H103.  I am right now a little foggy on that entire circuit.   Right now it works mostly, but sometimes bounces and makes an incorrect output.

But next keypress is always good.   Any way, I will try swapping out a few of those ICs with "HC" variety for the ones I already have in stock.  Most of the problems were caused I think by

corroded IC pins.    Took them out one by one and scraped each pin bright again using exacto knife.  A few were so badly corroded they broke right off while cleaning.

Put in some "LS" parts as I scrounged them up around here.  Got it working, but not perfectly, but good enough to do its job.

[Mac Doktor]

On May 26, 2024, at 10:13 AM, Leroy Jones <leroypu...@gmail.com> wrote:

That kit has 19 old old plain 74XX series TTL.  That keyboard draws 300 milliamps just by itself!     Those (32) 74LS273 ICs on the tube driver cards draw

another 500 mA.   

At least your fingers won't get cold.

I am seriously thinking of changing out those "LS" series chips with 74HC versions.   Much less current.   What do you guys think of that idea?

Sounds good but I defer to others on this.

I have a single board computer that I built from a kit around 1992. An 74HC demultiplexer went bad so I rummaged through the collection and found a 74xx. I stuck it in and everything worked fine. The only difference was that that IC got MUCH hotter. All I had to do was hover my finger over it.

I saw an S-100 computer back in the second half of the Seventies. The dealer had it tricked out with tons of RAM. That thing had a huge 5V power supply and got just a little warm.

On May 26, 2024, at 11:51 AM, Leroy Jones <leroypu...@gmail.com> wrote:

Most of the problems were caused I think by

corroded IC pins.    Took them out one by one and scraped each pin bright again using exacto knife. 

A pencil eraser may be better. Those silver plated legs can get seriously corroded. Add bad sockets that seize up and you have a disaster.

A few were so badly corroded they broke right off while cleaning.

Bally pinball machines where like this. The legs on the ROMs would snap right off. Fortunately, all you had to do was change a jumper or two and you could use EPROMs. 

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com

"If only you could see what I've seen with your eyes."—Roy Batty, Blade Runner

[Leroy Jones]

I had a bit of good luck last night with the old Radio Shack ASCII keyboard.   Went through my stash of various ICs and found

more modern, much lower current ones to replace 16 of the 19 on the keyboard circuit.   It is a smattering of 74LS, 74HC, 74C, 74HCT.

There is one socket where a 74HC193 will not work!   That portion controls the scan rate.   HC193 produces garbage output, where as 74LS193

works just fine.  Not sure exactly why.  But anyway, the end result is the total current at 5 volts is now 120 milliamps, and before swapping ICs, it

was up close to 400 mA.    Can do more and get it even less, but that means BUYING ICs.   

[Mac Doktor]

On May 27, 2024, at 12:54 PM, Leroy Jones <leroypu...@gmail.com> wrote:

Can do more and get it even less, but that means BUYING ICs.    

At leas they're not $200 apiece like certain Nixie tubes.

Terry Bowman, KA4HJH
"The Mac Doctor"

https://www.astarcloseup.com

“...the book said something astonishing, a very big thought. The stars, it said, were suns but very far away. The Sun was a star but close up.”—Carl Sagan, "The Backbone Of Night", Cosmos, 1980

[Leroy Jones]

Yes.  Exactly!   Last night there was a flakey problem with the 15-bit parallel data bus that connects to all of the tube driver latches.

There was a stuck bit.   Had to disassemble everything and eventually found a bad solder joint on one of the ribbon cables I made up

24 years ago!   Problem solved.  But during the troubleshooting, at one point I had to unplug the entire right side of the array and carry the assembly

of those 8 tubes into the kitchen to set it down in a safe place on kitchen table while I worked on other parts of it, chasing that stuck bus bit.

As I was carrying the aluminum channel with the 8 tubes and sockets, I thought to myself this is now a couple thousand dollars worth of tubes!

Jeez when I got them they cost 11 bucks each and I thought that was very high.   We are now in hyper-inflation guys!   News Flash!

[J Forbes]

The value of the stocks displayed on the tubes has gone up even more than the tubes themselves   :)