Brand and type: NSF M3 The name comes from Nederlandsche Seintoestellen Fabriek.
Originally they made telegraph keys.
This radio has serial no. 738. In 1926 the M3 was offered by 30 resellers in Holland. The "M" could be short for "meubel" meaning furniture, and "3" the number of tubes. All batteries needed should be placed inside the cabinet, thats's why it should be considered as a piece of furniture.
There's an article about this radio in the Dutch radio-collectors magazine. It says that the estimated amount of radios produced is 500. Probably 4 are left over nowadays. Well, now no.5 has turned up with a much higher serial no. On the radios tag is only space for 3 digits for the serial number! Here is a picture of the other radio. This radio is far from original, as the article describes, it was modified in some ways.
Produced: Hilversum, the Netherlands 1926
Cabinet: Solid mahogany, dimensions 50x27x23 cm. The front is made of ebonite. This is simple rubber in fact, but for the vulcanisation process much more sulphur than normal was added. This resulted in a material hard and stiff like wood and good isolation properties. Probably a wooden front wasn't suitable because of its ability to absorb moisture, thus giving bad isolation. The blackness comes from a certain amount of soot which was added in the rubber mixture.
Tubes: Three 4-pin triodes: A415, A415 and B405 as output.
Power: Three batteries: 4V, 90V and a C-battery (negative grid bias) which was adjustable by taps up to 20V. This C-battery I found inside the radio, totally worn out of course.
Bands: The radio can receive wavelenghts from 200 to 3000 meters, depending on the antenna coils used. These were made in the same factory. Five NSF-coils came with my radio.
Controls: The big knob left is for the tuning cap (of 1000 pF). It makes a 180° turn and the printing on it goes from 0 to 100. No fine-tuning feature. The 2 smaller knobs control variable resistors in the filaments of the 2nd and 3rd tube. Feedback is obtained by the moveable antenna-coil, which can be turned away from the feedback-coil. A bit odd, one would prefer to adjust the position of the feedback coil! But it all looks like done intentionally so I don't change it.
Obtained: This radio was part of the heritage of a Mr. Krijnen, whose depot had to be cleared out by fellow collector Gerard and me. We found several nice items, among which was this oldie. Also half a truckload of junk but that's no problem.
Here's Gerard in full concentration to get some decent sound from the old lady, in my workshop. He found that Megawatt stations nearer than 100 kms gave some audible results in the speaker or headphones. At first he didn't believe me when I said this was the best it would get - see below under Working.
Condition: This radio wasn't in great shape when we found it. It had been stored in 10 cm of water it seemed, for a considerable time. So the cabinet got a thorough treatment: grinding the stains off and giving it some layers of the proper varnish. Fortunately this kind of wood can stand some ill-teatment. But the bottom plate still is a bit crooked.
The front was cleaned using terpentine. All the metal parts on the front are nickel-made and were cleaned thoroughly. All text at the front is engraved and should be filled with white paint, don't know yet how to do that without making the rest filthy. The same goes for the engraved stripes and numbers on the knobs, they could use some fresh white paint too.
For the electrical part, I didn't have much trouble to restore that. It came without the tubes, so I had to find these first. Not so easy as we talk about vintage stuff. But now I have 3 working ones: I swopped about 50 new 30ies tubes for these 3 oldies.
The coil holders consist of an ebonite cilinder. One top was broken off, I could repair that invisibly with a liquid polyester, mixed with black wax for the right dull color.
One of the transformers was dead, it had a burned coil. Luckily I found an old guy willing to rewind it for me with very thin wire: only 0.06 mm in diameter. The transformers are German made, the brand is Körting, which is stamped in white on the black lacquered windings. Walter Groer from Muenchen confirmed that Körting, in Dresden, was a manufacturer of parts, especially tranformers, before they started to build entire radios.
Some wiring was changed, I put it back to original. All electrical parts are mounted on the fronts back.
Working: Yes but not very good, though I use a good antenna and earth. The tubes are old and tired so not much improvement can be expected.
Here is the schematic diagram of the radio. I guess it already was oldfashioned in the release year. This design is nothing to be proud of. Besides, my radio is different on details: the headphone is connected to the 2nd tube, the speaker to the 3rd tube. Philips made a much better radio only one year later, the 2514 for mains supply. I also have a home built receiver with better specs, than this expensive factory-built device. The price of this NSF at introduction was 198 guilders, a fortune that days. For that amount the batteries, headphones and 10 coils were included. Some years later the NSF factory joined the Philips family, but the NSF brand was still upright. I also have a NSF-radio from the 40's.