[David Dunlop]

The Project is in a temporary holding pattern for a while.

I realized once I had the spare C7D Trimmer Capacitor ready for installation, I did not have any 20 gauge tinned, solid copper hook-up wire available in black insulation to make up the two connections between the C7D and its related coil. I have now ordered a 25-foot spool from the local Electronics Shop and have to wait for it to come in for pickup.

In the meantime, I have continued to review the steps needed to do the swap of the Trimmer Capacitor in the Main Set Receiver. It has been an interesting process with several modifications taking place in my head over the last few weeks.

Step 1 is I have to unsolder the Grid Cap Clip for Valve V1D inside the front section of the receiver and solder on a temporary extension of about 6 inches. This lead only has 2-3/4 inches of free place with the Grid Cap Clip removed before the lead will disappear inside the coil shield. The shield cannot be removed because there is not enough clearance to do so with the front panel attached to the receiver. The extension will allow me to retrieve the Grid Cap lead and re-solder the clip to it when the swap of C7D is completed.

Step 2: On the back side of the receiver, as shown in the attached photo, The C7D Trimmer Cap is the top most component on the left hand diagonal IF Coil Assembly. From approximately the mid-point of the assembly to the top, there are three individual wires that will have to be unsoldered: a long one going up above the coil assembly and a medium and short length set at roughly the mid-point. With them free, the large wiring loom coming off the bottom of the coil assembly, leading to the SHARP/FLAT Switch is the only thing holding the coil assembly in place once its mounting screws are removed.

The two IF Coils are 3-3/4 inches long wrapped on brown phenolic tubes. Strips of cotton cloth tape hold them in place on the tubes and then the entire coils are dipped in bees wax to protect the very fine wiring of the coils.

The punched holes in the rear chassis panel have some pretty keen edges. It would not take much contact with them for the wax and wire coils to be trashed, so the entire assembly has to come straight back out of the holes roughly 4 inches to be safe.

The loom feeding to the SHARP/FLAT Switch has been sitting in that position for nearly 70 years and I have no way of telling for certain if it is natural or synthetic rubber. The wires have also been treated with fungicide varnish so overall are pretty stiff. There is only about 2-1/2 inches of play in that loom before it reaches its limit and the coil assembly will start to get pulled to that side. Not good.

My first thought was I would have to unsolder all the connections at the SHARP/FLAT Switch, which was not a popular thought in my head. I then remembered the disassembly process for the Spare Parts Receiver.

The only electrical connections at the back of this switch are to the two IF Coil Assemblies. The switch has a big long shaft that runs to the lower front of the receiver and the hole in the front of the chassis simply supports the shaft. The switch is actually held in place on the chassis by a mounting plate at the back end with two screws securing it. For reference, there is a photo of this switch in Post #633.

Step 3, therefore, will be to remove the knob from the front of the SHARP/FLAT Switch shaft and then remove its two mounting screws. The entire switch can then be moved back to clear the front panel of the receiver and then swung down and to the right in the attached photo to rest directly under the two IF Coil assemblies. It can then be careful moved straight back with the IF Coil assembly containing the C7D Trimmer Cap until the two coils clear the rear chassis panel. With lots of TLC…it should work…I hope.


David