Here is a possible answer to Jere DeBacker's question about the
simplified Repeat switch on late Duo-Arts [081004 MMDigest].  I was
hoping someone would answer this authoritatively, but since there
were no responses, here is my guess.

The two-tube switch either allows the two tubes to be connected or not;
it's as simple as that.  One tube has to go to the port on the take up
spool, so the other tube must go to the Repeat valve.  This seems to
mean that the Motor hole, on the right side of the tracker bar, has to
go directly to the motor switch.

Earlier models needed both the take up spool plus the Motor hole before
there was enough air to make the Motor valve turn off, so it would appear
that this is a much simplified mechanism that would not work as well as
the older one, since any perforation or tear on the right side of the
roll that goes over the motor hole will instantly turn off the motor.

The only other explanation I can think of would be that there is some
mechanism that works as follows:  When Repeat is 'Off' it allows some
mechanism to combine the signals from the take up spool and Motor hole
to turn the motor off, and when Repeat is 'On", then the electric motor
valve is disconnected, and the signal from the take up spool triggers
the Repeat valve.  The problem here is that I do not think I have ever
seen or heard of such a mechanism.

Can anyone out there help with this?

Randolph Herr