Key contacts

The console uses Kimber-Allen’s silver key contact rails. I’ve learned that silver contacts don’t work reliably at +5-volt logic levels, so I’ve breadboarded TTL-CMOS up/down level shifters to drive the contacts at a more organ-appropriate 15 volts. Here’s an updated schematic. I’ve also learned all about “wetting current”, which is the minimum current needed for a switch to keep its contacts clean and reliable over time. The 14501B level shifters can drive about 9ma per output, which I hope is sufficient. I’ve made an inquiry of Kimber-Allen to be certain.