TimPerry wrote:

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates are
tied together and go nowhere else. how does that make a diac?

You know, I'd never looked at that in detail. That's puzzling.

I do indeed use a diac myself in that application. Look at the Behringer EP2500
schematic, they copied it 'verbatim'.

Graham