Thursday 3 July 2014

1937 Marconi Restoration

The past few days have been spent refurbishing my next door neighbour's 1937 floor model Marconi radio...Model 82. All of the capacitors were replaced except for the micas, which seemed to still be in spec. Several resistors were also replaced as they had drifted far out of spec on the high side. Four tubes were replaced as well, after measuring low emission on my  Eico 667 tube tester. Additionally, several wires whose rubber jackets had cracked and disintegrated, were replaced. A new three- prong power cord was installed, along with a fuse holder on the back of the chassis.

The radio also had two small fixed bias cells....small 1.25V cells for supplying grid bias voltage to the AVC/IF stages.

Both cells had long ago dried so I tried to rejuvenate them  by following a procedure found on the web. The zinc casing was carefully pried up to remove the carbon covering disc and a few drops of distilled water were added to the dried-up crystals inside before re-sealing the case. The initial cell voltage of .11 VDC rose to 1.2 VDC after the procedure but I wasn't confident that the new 'seal' would keep air from drying the electrolyte out.

I decided to use small camera batteries (1.5VDC) in place of the original cells since they were very close to the same size. With heat shrink tubing surrounding the edges and bottom lip, they readily installed on top of the original holder and clamped solidly in place.

A small brass spacer was inserted into the cell holder to make contact with the bottom of the new cell.

I was pleased to hear how well the radio performed after all of the changes. I have attempted to record a short video (for the first time) using my I-Pad and then converting the video to mpeg format as well as trimming it slightly in newly-installed Windows Moviemaker freeware. Hopefully my videos will get better with practise!

Marconi Model 82 with 3' wire antenna

My neighbour will be pleased as the radio belonged to her grandfather and she remembers listening to it a lot as a child. She has been kind enough to let my hang my 100' three-wire LF flattop over the top of her house and property to a tree on the far side of her that's a good neighbour!

While on a roll I also cleaned and re- capped a mid 50's 'All American Five', Sylvania (model 515) that another neighbour had given me several years ago. It was so dirty and grimy when first received that it was hard to even tell what color it was. Two tubes were also replaced. It now resides on the kitchen counter and is sounding great, playing oldies only!

My restored Sylvania 515

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