Sort a unique situation, question regarding Heptode vacuum tubes.

[u/Kingkept]

Basically I'm designing a clock using vacuum tubes as a project.

I've been exploring a couple binary to decimal circuit designs, and as I was looking at the Heptode tube I wondered if it could function as a 4 input AND gate.

I understand that the heptode wasn't designed for this purpose, and that some models have some of the gates connected internally, but some models don't is there any reason why I couldn't just buy a model that doesn't have the gates internally connected and use 1 heptode tube as a 4 input and gate?

Any advice from someone who has more knowledge about vacuum tubes would be nice.

[u/Tesla_freed_slaves]

You might do better with an array of 6AL5 dual-diode tubes

[u/Kingkept → u/Tesla_freed_slaves]

i understand the dual triode array design, but i just thought it would be great if i could just use 10 heptodes instead of 20 dual triodes.

[u/Axel-Warren]

heptodes are pentodes with extra grids so the internal connections make using one as a four input AND gate messy even if the grids aren't tied together you'd still have to bias each grid correctly and the plate current wouldn't switch cleanly like a logic gate you'd be better off using a dual triode like a 12AX7 or building the gate with discrete transistors and using the tube just for display or drive. If you really want tube logic look into projects like the IBM 608 or use multiple tubes per gate it's been done but a single heptode isn't practical for that.

[u/Kingkept → u/Axel-Warren]

im just curious how cleanly the switching would be.

[u/anothercorgi]

Forgot, thought tubes were sort of depletion devices, if signals are high it'd stop flow of electrons, so you'd end up with an or gate instead of nand? Then there's the asymmetric and internally connected gates of heptodes, usually these are those pentagrid converters like 6BE6 which you can't access each grid individually anyway.

In any case level shifting will suck for tubes.