B7971 types

[Robert]

I have a B7971 with wires (no “circuit board”) but no top pin, dated early 64 and marked Burroughs, is this rare?

All the other wire ones I’ve seen have a top pin

Rob

[gregebert]

Share a photo; sounds interesting. I suspect it was an early prototype, and it was soon discovered that a substrate would be more manufacturable and durable.

[Robert]

Rob

On 7 Aug 2025, at 18:19, gregebert <greg...@hotmail.com> wrote:

Share a photo; sounds interesting. I suspect it was an early prototype, and it was soon discovered that a substrate would be more manufacturable and durable.

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[Jeff Walton]

Hi Rob,

 

The 7971 tubes that were wired are shown in the blue area.  The PCB styles are shown on the right.

 

 

In the tubes that I’ve collected, the early wire construction went from 63-64 and were replaced by the PCB style in 1964.  The wired versions had several variations of top insulators and posts.  In the photos, the earliest versions had just a small insulator and the top post.  Then they went to a full insulator and removed the top post.  When the PCB versions started, it was accompanied by a stiffer internal frame and mounting that removed the need for the full insulator and the top post.  The early tubes with the smaller non-circular insulator needed the post to hold the internal workings from moving up and down in the envelope and were more mechanically fragile.  The wired tubes with the full insulators had improvement in the frame and connection to the base of the tube.  By the time they got to the PCB version in 1964, the internal structure was much more durable and could withstand rough treatment compared to the earlier wired versions.  I have one tube that has both the post and full top insulator but I have not seen any more.  I suspect that there are a bunch of us with tubes stashed away that may have one or two of that variation.  One of my MOD-SIX clocks has a full set of wired 7971 tubes with the posts and I have a set of the full insulator wired versions in another clock.  The 7971 was a beautiful and well designed display!!

 

Jeff

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[Robert Norman]

Hi Jeff

Mine does not have the full round top insulator it has the rectangular one

Rob

On 7 Aug 2025, at 21:43, Jeff Walton <jwalt...@gmail.com> wrote:



Hi Rob,

 

The 7971 tubes that were wired are shown in the blue area.  The PCB styles are shown on the right.

 

<image001.png>

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[Jeff Walton]

Sounds like just another variation as Burroughs moved from the wire to PCB internal construction. 

My earliest tube DC is 6349 and it has the post with full top insulator.  Between 6403-6444, all of mine are still wire backplane. My first PCB version is DC 6520.

Not sure when the last tube was made.  I have a 6821 DC as the newest for me.  I think that there is someone in this group that has more complete info. 

Jeff 

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[Robert]

I don’t have any with the full top insulator, my earliest ones are  dated 63-52

Thanks

Rob

On 7 Aug 2025, at 23:39, Jeff Walton <jwalt...@gmail.com> wrote:



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