Marconi 290

Manufacturer: Canadian Marconi
Model: 290
Approximate Date Of Manufacture: 1940s
Type: 5-tube Superheterodyne AC/DC AM broadcast band radio
Tube lineup: 35W4, 12BE6, 12BA6, 50L6GT, 12AV6
Status: working, partially restored
Where purchased: eBay, April 2004

Description

The is a 5-tube AC/DC AM broadcast band radio with a brown bakelite case. It features an unusual bottom loading case. There is a phono input on the back which is always active, so presumably when in use you need to tune the radio to an unused frequency. It uses all miniature tubes except for a 50L6GT. Strangely, the tube layout diagram label on the bottom of the radio lists different tubes from the ones in the set (not even the same size tubes).

When received it was missing one knob. The line cord was extremely brittle and the insulation was falling off. It was very dusty, with a little rust on the chassis. It was working quite well when I received it (after fitting a new line cord). The dial glass is broken. Someone has made a crude replacement piece for the missing third of the glass but it has no frequency indications on it. I am planning to make a replacement dial glass. I was not able to locate a schematic diagram. The set has very few parts, including only 5 paper caps. This is partly due to the use of a 6 pin network circuit (a thick film hybrid containing some resistors and caps in a 6 lead ceramic package).

So far I have cleaned the case and chassis, replaced the line cord and all electrolytic and wax paper caps, and glued the loose internal antenna. I still need to find a replacement knob (or two suitable knobs).

There are two holes in the front grille. I can see from a picture on the schematic that there was a name plate with Marconi written on it, probably made from brass. I need to obtain or make a replacement.

I made a replacement for the dial glass. I had a friend make a high resolution scan of the original. I then cleaned up the image and filled in the missing portion using an image editing program (The Gimp). Rather than trying to cut a curved piece of glass, I bought some plexiglass and cut a replacement for the dial glass. Some test prints of the the image onto paper were made to get the correct size for the dial glass lettering. The next step was to print the image onto a transparency sheet and attach it to the plexiglass dial glass.

Pictures

The radio as received.

The knob that I need to find a matching replacement for:
Radio knob

The dial glass. The piece on the right was (crudely) made by someone and simply painted brown.

At bottom, a 0.1uF 600WVDC capacitor circa late 1940s, and above a modern equivalant.
Comparison of caps

Below, four views of the chassis after cleaning and recapping.
Radio chassis

Someone has written "1966" in grease pen in the chassis. Maybe the year it was last worked on? The electrolytic cap does not appear to be original.

Here is a small version of the image for the dial glass after adding the missing part and cleaning it up:

Dial glass

Here is the radio after cleaning and with the paper prototype of the dial glass attached to the plexiglass replacement (no, I didn't find a replacement for the missing knob, I manipulated the image):

This rear view shows that the cases extends to the back of the radio. It looks very clean, but the side effect is that the external antenna connection is just a wire hanging out the rear of the case!

Here is the picture from the service manual that gives some idea of what the Marconi name plate should look like:

I saw the same model in a local antique shop. It had both knobs but the dial glass did not look original and it did not appear to be in working condition. They wanted $95 for it -- too much!