Posts Tagged ‘broadcast radio’
A few weeks ago I had one of my rare visits to the post office. As I was waiting, I saw a display of a new series of stamps and I just had to buy the one shown here. What caught my attention was not really the artist, but rather the Kurér portable radio.
The stamp was of course not about the radio but was issued in commemoration of the 100 year anniversary of the birth of Alf Prøysen. The English Wikipedia page has this to say about him:
Alf Prøysen (23 July 1914 – 23 November 1970), was a writer and musician from Norway. Prøysen was one of the most important Norwegian cultural personalities in the second half of the twentieth century, and he made significant contributions to literature, music, TV, and radio.
One of his main characters was “Teskjekjerringa” called Mrs. Pepperpot in English. She is shown here in the second stamp in the series. I remember this story very well from my own childhood in the 60’s as told in the characteristic calm and soothing voice of Prøysen himself. The character eventually appeared in 23 different languages. The radio is of course here because this and others of his plays were very popular on radio in the 50’s and 60’s.
And it was this radio, the Kurér (= Courier), that made me buy the stamp. It was a highly successful portable radio from the Radionette factory in Oslo from 1950 to 1958. It has four valves and covers long wave, medium wave, ‘ the trawler band’, and short wave. It has room for batteries (90 Volts and 1.5 Volts). But luckily it also has a built-in mains supply – the 90 Volt battery is hard to find these days. A total of 224 000 were produced and it was exported to many countries especially in the Middle East. It is very easy to repair even today.
I would think the most popular version today among collectors is the dark red one shown in the stamp. I have a grey one shown here with a simple medium wave transmitter that I have described before on top.
The Model One has been a huge success. But in many ways it is a daring retro design judging from all the features that are missing in this radio. I am thinking of features such as a customizable equalizer, a digital display, and memory presets. It just has a plain old analog tuning dial for FM and AM.
The radio could as far as I can tell just as well have been made in the 70’s except for some of the IC’s which are used. Actually it is easy to see the similarity with the even older KLH Model 18 from the 60’s, and yes – Henry Kloss played a role in both radio designs. But that makes for easy repairs, such as a seemingly common fault in the FM tuning capacitor, which over time may develop contact problems.
The radio is in many respects exceptionally well made. The tuning dial has a quality vernier drive. The audio section is well built with a powerful amplifier, a strong magnet for the loudspeaker, and a bass port design for the wooden cabinet. All are factors which contribute to its reputation for good audio. If one can trust measurements on the web, it has been equalized for enhanced bass and treble with the mid’s some 6 dB down. These are well-known tricks for getting a warm and crisp sound with universal appeal. Internally the tuner section, which is built around the TEA5711T chip, is well shielded for frequency stability as seen in image 2.
One weakness which manifested itself after only 3-4 years in this particular radio is that it became hard to tune, scratchy, and unstable on FM due to intermittent contacts in the tuning capacitor. According to the TEA5711T datasheet it is a varicon which for AM has 140/82 pF, for FM 2 x 20 pF, and for trimmers 4 x 8 pF. This particular unit had a Mitsumi varicon. Some say, when this fault occurs, that the varicon must be replaced and others say it can be cleaned. Who do you think I sided with?
Disassembling the radio is quite straightforward if you are used to this kind of work. The tuner is enclosed in shielding on both sides of the PCB. The shields can carefully be desoldered as shown in image 3. That exposes the varicon, and its plastic casing can be lifted as shown in the last image.
I sprayed it with contact spray and the radio came back to life. The only problem was that the tuning on FM had shifted so that a station on 100 MHz now appeared on 107 MHz. A little detective work around the circuit showed which trimmer that was for the FM oscillator and which one that was for the FM RF circuit (marked O and R in image 2). Since the oscillator trimmer was set for its maximum capacitance with the plates covering each other, it was easy to reduce the value and get the FM dial back to normal again, and then to peak the RF trimmer.
It got me wondering though to see that it had been necessary in the first place to have the oscillator trimmer set at its maximum value. It was just as if the tuning capacitor never had had its full value, even in the factory, and that it finally got it after my cleaning.
As I was clearing out my childhood home I came across an old radio that my father had tucked away in the basement. It was a German Blaupunkt radio, and what a historic dial it had!
It turned out that my father had himself found it as he was clearing out his childhood home many years before and that it had belonged to my grandfather who died in 1959.
It covers longwave, medium wave and three shortwave bands from 5.5 to 21 MHz. I had never before seen a radio with a dial given in meters rather than kHz or MHz, but I have later understood that that was not uncommon for pre world war II radios.
Since the back was missing, I had no information about age or type. The tubes which were all in the 11-series suggested the end of the thirties, but here it turned out that the dial had valuable information.
The medium wave part of the dial had a separate side on the left hand for German stations and here one can find cities that are no longer in Germany such as Königsberg on 223 m and 291 m (1348 and 1031 kHz). Today this is Kaliningrad in Russia. The dial also showed Danzig on 230 m (1303 kHz), ”Schles. G. W.” (Schlesische Gleichwelle – a single frequency net with stations in Gleiwitz and Reichenbach/Oberlausitz) on 244 m (1231 kHz), and Breslau (315 m – 950 kHz). Today these are the cities of Gdansk, Gliwice and Wroclaw in Western Poland, an area which was in Germany until the end of the war. At least the radio must have been from before the end of WW2.
But there were a couple of more names with a lot of history in them. Troppau can be found on a wavelength of 249 m (1204 kHz), a frequency which it had until September 1939. Today Troppau is called Opava and lies in the Czech Republic. Troppau lies in the Sudetenland which Germany annexed on 30. September 1938. Finally one can find Memel on 531 m (565 kHz). This city is today called Klaipeda and lies in Lithuania. It was occupied on 22. March 1939 as the last German annexation before the outbreak of the war on 1. September 1939.
Thus the conclusion of this historic search across the dial is that the radio dates from some time between March and September 1939.
With some cleaning the exterior turned out to be quite nice. I thought to myself that I cannot give up now, so on inspection I could see that a couple of electrolytic capacitor had been replaced, probably by my father. It had the following tubes: ECH11 as mixer/oscillator, EBF11 and EF11 for the intermediate frequency stages, and EFM11 for the magic eye and the first low frequency amplifier.
The output tube and the rectifier were missing, and it was natural to look for tubes in the same 11-series. I was not able to find this particular radio in the large archives of the Norwegian Radio History Society, but there was documentation for a few other Blaupunkts there. From their descriptions I could guess EL11 for the output tube. Measuring the filament voltage for the rectifier gave 4 Volts, so then AZ11 was a good choice.
With some excitement I turned on the voltage for the first time, and to be on the safe side I connected it in series with a 60 W light bulb to reduce the voltage. No explosion! As incredible as it sounds, with full voltage it actually produced sound. But unfortunately after a few seconds everything disappeared. One evening with diagnosis of the radio and I could isolate the problem to the beginning of the audio section and two rotten shielded cables connecting audio in and out of the pentode in the magic eye. Not everything is as new after 60 years! After having replaced the cables the radio was perfect, and even the magic eye and the dial lamps functioned. In my experience the magic eye is often weak and in the Oslo region the dial lamps for the longwave band may have burnt out as the local station used to be on 218 kHz.
Some weeks later as I was about to clean the dial for dust I disassembled the glass in the front and found an inscription saying Blaupunkt 7W79 and the date 28.3.39. So the result of my detective search wasn’t too bad! In fact the dial was produced with an updated name just 6 days after the occupation of Memel/Klaipeda.
This radio cannot have been more than a couple years old when all radios were confiscated in Norway in 1941. Imagine how sad it must have been to give up such a nice and costly radio at that time! This must also have been one of the few radios that actually were returned to their rightful owners in 1945.
Now the radio has a prominent place in my house and every time it is turned on it is a reminder of both the history of my family and of a turbulent era in the history of Central Europe.
First published as “Min farfars Blaupunkt radio” in Hallo Hallo of the Norwegian Radio History Society, September 2001, updated in 2013. © Sverre Holm