28-03-2018, 09:42 AM
I'm not sure that a cam is the appropriate description, Mike, although we may both be thinking of the same thing.
I've unearthed a Home Radio catalogue page where they are described as Reverse Vernier drives - only 4s 9d each!
The illustration isn't particularly clear, so I've tried to draw it out more clearly.
The brass ball race housing has a rebate where the steel spindle enters. A pin through the spindle engages with the raised ends of the rebate and drives the dial cord at normal speed.
Incidentally, an alternative method (but not suited to a portable receiver for obvious reasons) used by PYE had a hefty flywheel mounted on the back end of the tuning spindle. The cord drive reduction was reasonably high but the flywheel action meant that it could tune from one end of the scale to the other very quickly. My particular memory of these drives was the lovely silky feel to the tuning knob when make fine tuning movements.
I've unearthed a Home Radio catalogue page where they are described as Reverse Vernier drives - only 4s 9d each!
The illustration isn't particularly clear, so I've tried to draw it out more clearly.
The brass ball race housing has a rebate where the steel spindle enters. A pin through the spindle engages with the raised ends of the rebate and drives the dial cord at normal speed.
Incidentally, an alternative method (but not suited to a portable receiver for obvious reasons) used by PYE had a hefty flywheel mounted on the back end of the tuning spindle. The cord drive reduction was reasonably high but the flywheel action meant that it could tune from one end of the scale to the other very quickly. My particular memory of these drives was the lovely silky feel to the tuning knob when make fine tuning movements.
