I'm trying to gain some understanding of how early computers were built; as discussed in What accounted for the cost of ENIAC? the cost of first-generation computers was not necessarily mostly about the cost of purchasing the components; much of it was about the costs of assembly, testing and suchlike.

In later decades, printed circuit boards came to be heavily used, but as I understand it, not only had they not yet been invented in the forties and fifties when vacuum tubes were most heavily used, but PCB materials do not stand up well to continual exposure to concentrated heat sources like, well, vacuum tubes.

Wire wrap was used in the transistor era, the sixties and seventies, not just for prototyping, but also for manufacturing. It would seem on the face of it to be suitable for vacuum tube computers. On the other hand, I found this discussion: https://www.diyaudio.com/forums/tubes-valves/287205-vacuum-tubes-wire-wrap.html in which a poster suggests wire wrap and vacuum tubes do not mix:

However, after much experimentation, it became clear that wire wrap was only good for the short term, by itself. If the piece of built-stuff flexed much, then eventually oxidation would set in and make some one of the hidden dozens-to-hundreds of connections vexingly noisy. And never when debugging.

That would seem to leave vacuum tube computers to be constructed by 'point-to-point construction' which seems to be the technical term for 'just solder all the components individually'.

This is counterintuitive; it feels to me like wire wrap should be more resilient than soldered joints, therefore better able to withstand thermal cycling. But I'm no electrical engineer; my intuition might be wrong. And while I can find plenty of mention of transistor computers being built (for production, not just prototyping) with wire wrap, I cannot find any mention of vacuum tube computers being so built.

Were any vacuum tube computers built with wire wrap? If so, did it work reliably? If not, why not?

  • 2
    I disagree that wire wrap is more resilient than solder - while it’s true that soldered wires are prone to fatigue, which could be an issue when subjected to vibration but not heat cycling. On the other hand, a wire wrap connection is essentially a spring contact where the wire itself is the spring, wound round the pin, therefore the slightest change in geometry (such as heat cycling) could compromise the joint.
    – Frog
    Apr 14, 2021 at 6:18
  • 2
    The original Macintosh prototypes were wire wrapped (according to folklore.org) so wire wrapping continued to be used for prototyping at least into the early ‘80s. Apr 14, 2021 at 11:11
  • 8
    @Frog. A properly made wire wrap is not a "spring contact". The connection is actually welded together by the pressure on wire on the sharp corners of the square pins, as it is wrapped around the pin with a special tool.
    – alephzero
    Apr 14, 2021 at 13:40
  • 2
    @alephzero you might hope so, but having unwrapped quite a few I’ve never encountered perceptible evidence of this. I can imagine that an atomic-scale weld would be beneficial for conductivity but it doesn’t provide much mechanical reinforcement, based on observation- certainly not by comparison with a soldered joint.
    – Frog
    Apr 14, 2021 at 19:26
  • 2
    I've wrapped and unwrapped several prototype boards (Apple and Amiga). Some wraps were pretty loose. Definitely not welded.
    – hotpaw2
    Apr 16, 2021 at 3:50

2 Answers 2


Wire Wrap as used in computers is simply a later development then the ENIAC or vacuum tubes in general (*1).

The Keller tools were first marketed in 1953 and it took a few more years until they made their way from telephone to computers. IBM might have been the first, around 1960, a bit before the /360 came which, used it a all over.

*1 - In contrast, PCBs were developed prior to the ENIAC. But yeah, not really widespread enough to make it worth using a new technology like that.

  • 1
    Another question (I don't know the answer!) would be the availability of wire-wrap vacuum tube bases. The pins in conventional (soldered) tube bases are simply hollow tubes with the vacuum tube plugging into the hole at one end and the soldered joint at the other. A wire-wrap pin with a hollow tube at one end and a square pin at the other would be more expensive to manufacture. But apparently some audiophile vacuum tube enthusiasts prefer wire wrap construction because it gives "better sound quality."
    – alephzero
    Apr 14, 2021 at 13:53
  • 4
    @alephzero Audiophiles would bark at the moon if someone told them they would get better sound quality. I'd rather trust an oscilloscope! ;)
    – J...
    Apr 14, 2021 at 16:36
  • 1
    @J... I'd say they do as well - oscilloscopes can be used much like tea leafs :)
    – Raffzahn
    Apr 14, 2021 at 17:14
  • 2
    @alephzero - Do they also use special highlighter pens to mark the edges of the tube's glass envelope too? Because that works for CDs, you know ...
    – davidbak
    Apr 14, 2021 at 20:09
  • @davidbak I know we're going deadly OT, but I have to ask: REALLY? They are seriously doing such? I guess there is no thought to strange to occur to a human.
    – Raffzahn
    Apr 14, 2021 at 21:08

Not sure I would trust 30 gauge wire wrap wire insulation with vacuum tube plate voltage. The cross-talk at the higher voltages plus digital edge speeds would also be far worse.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .