Museum Hours:

Saturday 10-6

Sunday 12-5

Early Electronic Television

Marconi 705 Restoration

This mirror-in-lid set has arrived from England. The cabinet is in poor condition. We begin the restoration by taking a number of pictures of the inside of the cabinet, showing the wiring and chassis location. As the chassis are removed, more pictures are taken.

Restoration of this set is now complete. Here are pictures of the restored set.

The Cabinet. (pictures) All of the metal parts have been removed and the cabinet has been taken to Old World Furniture Restoration. They are concerned by possible beetle infestation in the lower part of the cabinet, so the first step will be to put the cabinet in a plastic container and fumigate it with insect spray for a few days.

The cabinet has been stored in a damp place for some time, and the veneer has delaminated in many places. The front panel may be too badly damaged to use, and the top panel with the radio dial may also be beyond repair. After all the veneer is removed a decision on what can be salvaged will be made.

Old World has stabilized the wood frame and has installed new veneer. The cabinet is now complete. Here are pictures of the restoration process.

We will install the chassis next to complete the restoration.

The Chassis.  There are three chassis in this set. One contains the two power supplies, one for the circuitry and one for the picture tube. The Audio/Video chassis contains the RF amplifiers, video amplifier, sync separator and sweep circuits. The final chassis is the AM/SW radio.

Power Supply Chassis.  (pictures) The power supply chassis is badly rusted. All the components will be removed and the chassis will be replated. In addition, there is evidence that one of the transformers is overheating (tar has leaked onto the bottom plate). Before removing the components I will apply power and see if the transformers overheats. The EHT transformer is defective, and the company I use here in the U.S. cannot deal with the tiny 45 ga. wire used in it. I have sent it to a company in England for rewinding. The high voltage (EHT) capacitor also had to be rebuilt.

The transformer is still not back from England. The chassis has been replated, and we have reassembled the power supply. We have installed a temporary high voltage (EHT) transformer until we get the original back.

Audio/Video Chassis.  (pictures) This chassis is also badly rusted. Since most of the components are on a single terminal strip underneath, it will be relatively easy to remove all the components and have the chassis replated.

I was able to remove the rust using steel wool, abrasive cloth, and rust removing chemicals. Though it isn't perfect, I have made the decision to restore the chassis as it is, rather than stripping it and having it replated.

I have completed rebuilding the paper and electrolytic capacitors.

After assembling the power supply, we put the picture tube back in its assembly and connected the cables to the audio/video and power supply chassis. When we applied power, the set worked immediately, with a good, sharp picture.  All that remains is connecting the radio chassis and testing the TV sound function.

After finding a fault in the IF stage of the radio, the TV sound works well. The set is now ready to be reassembled.

Radio Chassis.  (pictures) The radio chassis has almost no rust. After cleaning, we will replace all the paper capacitors and check the electrolytic capacitors. The radio chassis has been restored.

Picture Tube Assembly.  (pictures) The picture tube is mounted in a metal enclosure, which is in good condition. All that will be required is cleaning.