I have looked at the switch on the left hand arm.
It has electrics in there as there appears to be a stop switch.
Would this model have AC erase as there is already wiring in place for the stop switch?
The right hand arm can be clearly seen to straddle both the groove disc and the recording area so that makes sense to me.
i belive the switches to cointrol the function were built in to the mic assy
this i do not have
and can find no circuit
The tracking and record is all in the right hand arm.
This is the reason that the "pickup head" is so wide. The left hand side of the head has the stylus which locates in the central tracking grove and the magnetic Rec/RPlay head is on the right hand side, the magnetic medium being in the form of a disk which is placed under the tracking disk. I assume that only the area not covered by the disk is coated with the oxide although I have seen large EMI disks which are fully coated!
The switch I magnified looks like it could be a limit switch to stop the head crashing into the tracking disc.
I was thinking that the erase head may be on the left arm.
The 1960s Philips one I have does have the stop and start switches in the microphone casing.
I see it as a relatively small challenge to make something up provided a plug could be found or made up.
There is a little bit of a challenge finding the bulk recording tape material for the recording media too.
The switch I magnified looks like it could be a limit switch to stop the head crashing into the tracking disc.
The head would have to be too far over to the left to trip that switch, ref (and have passed through the centre spindle!). It looks to me as though the switch has an interlock to stop inadvertent operation so I guess that it is an erase on/off switch 
That is what I was thinking. The erase head looks like it will be in the left hand arm.
It looks like you switch it on to erase the disc and when it is done and the head gets to the center it pushes the little rocker that nudges the switch off.
Hmmm! Did the machine have a tracking erase head or a "blanket" device? Editing would be a luxury in the office environment would it not? I also cannot see how the right hand arm assembly can operate the switch without hitting the centre spindle! I am sure that the little device by the switch is a simple "anti-oops" interlock! Has anyone found an operating manual? A few years ago, the EMI archives would have been able to help - not any more. Bring back Ruth Edge, the excellent archivist who was always incredibly helpful!
I was thinking along the lines of something in the left hand arm for erasing.
There is a track visible along the top of the left arm leading up to the rocker device that looks like it could operate the switch.
The other end of the rocker is not visible in the photo.
I have just come into possession of a battery/windup version of the EMI dictating machine.
The 'motor' is clockwork and the rest is run off the batteries.
Additionally there are around 5 spare magnetic disks with it too.
So if someone needs a disk then PM me.
Andy
