Wireless Set No. 52 Canadian - Project

[David Dunlop]

Continuing with the COUNTERS and their Coupling arrangements, lets take a look at how the Canadian Marconi Company dealt with this issue on the two PA TUNE Coils in the 52-Set Sender.

At the moment, the two in my Sender are still in situ and next to impossible to get at, so I will resort to using the illustrations of the relevant parts out of the Master Parts List.

The first photo is the Coupling Arm that is fitted to the COUNTERS side of the drive system. It is a tapered metal channel with a large post fitted to the wide end which serves as the mounting collar. Roughly midway down the channel an small capped pin is fitted and at the narrow end, a small slot is centered parallel to the longitudinal axis of the channel.

The second photo is of the Coupling Arms that fits on the Coil side of the PA TUNE drive assembly. This one is a rectangular, brown, phenolic plate with a small bushing post at one end and a small pin at the other. This pin has a small hole through it at the top end.

The third photo is the Coupling Spring, which when installed, provides tension to the entire Coupling Drive Assembly to remove any play in the system. In this configuration, the COUNTERS would be set to “))))” and the Tuning Wheel on the relevant coil brought all the way forward to its start point. The two Arms would be parallel and one over the other, such that the pin in the end of the Phenolic Coil Arm, passes through the slot in the steel COUNTERS Arm. When all was in place, the straight end of the Springs would be inserted in the small pin and the angle midway down the springs placed around the capped pin on the COUNTERS Arms. The curved end of the Springs is then brought across the COUNTERS Arms to wrap around the base of the large bushing. The end result is shown in the last photo.

This design also produced a drive mechanism with no slop in it at all and an instant response from the COUNTERS Dial as the PA TUNE knob is turned and the Wheel on the coil starts to move. What I don’t understand at the moment is why Marconi used two entirely different designs for basically the same purpose.


David