[Bear2Biker]

Yes I've often wondered what the pip was for, I have several 4 & 5 pin valves with this feature, I wondered if it was for the radio servicing chaps, the back of a radio can be very dark to see what your doing, so the pip can easily be used to work out the pin biasing in conjunction with feeling for the screwhead or rivet securing the valve socket in the chassis.

Nearly all 4/5 bases I've come across have the same orientation & if it's wrong first time just rotate 180, no forcing/bent pins.

Many noval valves use that idea, having the widest pin gap facing one of the mounting flanges, of course more difficult on skirted bases but still doable,.