I'm still a bit puzzled by how to do logic circuits with tubes.

Looking at an old report about transistors, I see the following diagram using DCTL (Directly Coupled Transistor Logic, such as used in the CDC6600):

Doing a XOR is pretty easy, thanks to the ability of transistors to work in parallel (OR) and series (AND).

At first sight, triodes can only do OR because the voltage differential between anode and cathode is so high !

The differential is usually overcome with a coupling, DC-blocking capacitor, at least in audio circuits, which makes the tubes work only in pulse/transient mode, which is not desired.

The pentodes have differentials of 0V-45V-60V so maybe a 15V Zener could work to make AND gates, but am I daydreaming ?

I should look at the schematics of the ENIAC, when I find the link again.

Thanks to the many comments on https://hackaday.com/2017/04/15/hackaday-prize-entry-hot-logic I found and recovered several resources about tube logic.

Daaaammmnnn....

For example I found the following circuit in the IBM 604 manual (1958 era):

What ?

Resistors ?

-100V ??

Maybe I'm too modern and I know "it works" but I think it's just ridiculous...

Other converging resources about the ENIAC, covered by @Al Williams:

http://archive.computerhistory.org/resources/text/Knuth_Don_X4100/PDF_index/k-8-pdf/k-8-r5367-1-ENIAC-circuits.pdf

The data matrices use resistos, not diodes...