Grateful Dead 1974 tour rig and microphones

Can anyone throw light on the vocal mics used in the Grateful Dead’s 1974 concert video linked below? It looks like a pair of interference tubes linked to a bespoke summing box…or a very early dual vape pipe/mic prototype?

Also on view, with horrifying relaxed OHS rigging practices, is their legendary Wall of Sound speaker system.

All in all, well worth a look…times have certainly changed!

https://youtu.be/JOciFuV2APg?si=r2DCqi8xZbiAv5w6









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