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Philips 204U, 1941

 

 

Description: These very small sets have an interesting design history.  Originally a Philips design, it was "acquired" for production in several German factories during the first years of WWII, under a number of designations, but with basically the same appearance and circuits and parts. The tubes are from the newly developed 20 series by Philips, of small size, using a "loktal" socket (like in the US), but using the center "chimney" also as a connection.  Miniaturization of many parts allowed a radio to be built that had excellent performance.  The radio on top was manufactured by NSF (Nederlandse Signalbau Fabriek, I believe), a close associate to the Philips firm. The bottom one was made by Philips Aachen (Germany), most likely during WWII.  The basic design was made in three variants: the 203U with Medium and Long waves, the 204U with Medium and Short waves and the 208U with Long, Medium and Short waves.  The oscillator and converter is a UCH21 tube, a triode-hexode.  This is followed by another UCH21 working as IF amplifier (the hexode section) and Audio preamplifier (the triode).  Then, a UBL21, double diode-power pentode does the detection and AGC voltage generation and the power output.  The half-wave rectifier is a UY21 in these sets.  Other variants used a UY1N, a very similar tube, but with octal socket. The Aachen version has slats for ventilation on the top of the case, something very much needed in the other radio.

The circuit of the radios were designed with economy in mind, the number of parts is smaller than one is accustomed to seeing in European radios of the late 30's.  The volume control, for example, provides not only its main function of changing the audio drive to the triode preamplifier, but it also carries the DC bias for that triode, derived from the AGC. For that reason, as the potentiometer becomes old, the typical scratching when changing volume has become a powerful noisy scratch that is not easy to overcome. Sprays perhaps have helped a bit, but not much.  The adjustment of the IF transformers seems devilish to me.  There are two intertwined soldered coiled wires that carry a magnetic core at their tips and are placed in the center of the IF transformer tube.  Presumably, shortening or lengthening the wires changes the adjustment of the transformers. I have not wanted to mess around with that in these radios.  They work pretty well as they are, particularly with the new Philips and Mullard tubes I have installed.  The condition of the UBL21 is rather critical to performance. The power pentode section is not terribly important, but the double diodes are.  As the tube ages, it seems that the detection process is severely handicapped before the power pentode weakens noticeably. I am using them at 117 Volts,  although they perform better at 220 with an up-transformer, but I do not want to stress the components too much.

Circuit: 4-tube (5-tube function) superheterodyne, AC/DC, Medium and Short waves. 

Tubes: UCH21, UCH21, UBL21, UY21

Source: Both sets came, at different times, from my friend Lutz-Dietmar Schmidt in Berlin, Germany. 

Date acquired: November 2001 (NSF) and 2007 (Philips Aachen)

Initial Price: 190 DM, plus shipping for the NSF.

Schematic: In my files

Condition: Both cabinets are in rather nice condition.  I had to change a number of capacitors and all the tubes, although the original ones still played.  The potentiometer of the NSF scratches loudly, but it is OK once set to the desired volume.  The potentiometer of the Aachen does not scratch, and it has a different construction. The back cover of the NSF is not for this particular set, but for a 208U.  The cover for the Aachen is correct for a 204U, but the chassis is a bit peculiar.  It appears to be correctly a 204U, except that it has an intermediate position in the band switch which is in the wrong position, if one is to trust the dial plate indications. There are coils for the intermediate position, but I have not been able to determine whether it is Long Wave, in which case it would be a 208U.  The power resistors of both radios have been partially replaced, as they were damaged. The tone quality of the approximately 5" speaker is remarkably good for its size. It should be noted that these sets work rather nicely when they work, but they can fail very easily because of the sockets that are used. The metal that makes contact with the tube pins becomes easily dirty or corroded, particularly the cathode connections, done through the central chimney.  Repairs and part exchanges are also quite difficult.  None of the electrolytic capacitors are original, although I have left their cans in place.