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Philips B8X44A radio (1964)

The B8X44A was one of Philips' top models of its time. It was one of the last "Plano" models, as the "Plano" form factor was becoming less fashionable and flat case audio equipment with separate speakers came en vogue. This model has FM stereo, and "Rapidosound" and "Intercom" options. Its sound is good, but the bass is not really great, in spite of the large speakers.

The B8X44A is a so-called "Plano" type of radio: radios that were built as flat as possible while their speakers were still built-in, usually on the sides.

Chassis front view

Front view of the chassis and dial.

The B8X44A was an expensive luxury model. It has a nice veneered case and must have looked modern at the time. It is an early FM stereo model, stereo broadcasts in Holland having started in 1963. As an extra feature, it has connections for extra speakers that can be switched on and off, and it has an "Intercom" function. That is, if you push one of the "Intercom" buttons, one of the speakers in the radio is used as a microphone, and the signal is output to one of the external speakers. This model also has a "Rapidosound" button, a Philips word for "stand-by". It means the heaters are kept warm so that when you switch the radio on, you will have sound immediately. Handy with the Intercom function, maybe.

The radio contains 9 valves and a number of semiconductors:

I got this radio in a barter for the B7X14A luxury plano. I wanted a plano with FM stereo that covered the full FM band. This one looked like it did not need much work, just some cleaning. Well... Something within the FM tuning mechanism was a bit stuck, so the needle only moved from 90-95 MHz. One of the metal skins of the pushbuttons was missing. And none of the pilot lights worked.

Chassis seen from behind

Chassis taken out of case, seen from behind. Awkward to service.

So I started the repair, which is a risky task with this one. Before you can even think of taking the chassis out of the case, you'll first have to disconnect and remove the speakers. Then you unscrew a couple of nuts to release the brackets that hold the pushbuttons, pilot lights and balance control wheel. After that, you can remove the bottom screws and carefully slide the chassis out. On your workbench, it will rest on the tone control knobs and the pushbuttons for the frequency ranges. The brackets with pushbuttons for the extra functions and the pilot lights will dangle by their cable harnasses, that are not long enough to lay the brackets safely beside the radio so you must constantly check you are not causing a short circuit. There is no easy way to stand the chassis on its side. You'll have to use plastic boxes and miscellaneous support material to keep it from falling over. I broke one of the pushbutton switches when trying to stand the thing upside down. Fortunately, the broken pertinax (phenolic paper board) part could be repaired using 2-component epoxy glue.

I dusted and cleaned the inside and noticed the driver board for the stereo pilot light was dangling loose. The fixing screw had disappeared. After replacing the pilot lights, I noticed that the stereo light never lighted.

	  Detail with stereo decoder in the back.

Detail with stereo decoder in the back.

Measuring the signals on the stereo board, I saw that the pilot tone feeding into the driver board was very weak. But I did seem to hear a little bit of stereo sound, so it could not be the stereo decoder? Well, yes. I opened the stereo decoder and measured the signals. It looked like the pilot tone was very weak. Feeding the decoder a 19 kHz test signal, it turned out that the pilot tone amplifier, a selective amplifier with two LC circuits, was misaligned, because it peaked at 21 kHz instead of 19. I tried to fathom the secrets of the decoder by studying the circuit diagram. After that, I was confident to try and adjust the amplifier, though there are no adjustment instructions in the service manual. This worked. After aligning the coils in the decoder, the amplification of the stereo pilot tone went up by a factor of 50, which was enough to drive the decoding matrix and markedly improved the sound. The pilot light did light now, but only on the strongest of stations. I replaced the small electrolytic that smoothes the rectified pilot tone, and that did the trick. I also checked the detector curve of the FM detector. I must admit that is was not as symmetrical as desired, but after all the trouble with stuck and broken cores I had had adjusting the B7X14A, I decided the slight improvement to be expected wasn't worth it

These Plano radio's have a diffusion screen to spread the light for the tuning scale illumination. This is a sheet of plastic suspended by 4 springs. As in many other planos, the plastic sheet had become brittle and cracked. It had fallen down and blocked the movement of the tuning mechanism. I replaced it by a sheet of professional drawing film. This is a mylar film with a matted coating on one side. It is slightly more transparent than the original film but does the job well. After this, I cleaned the case and the knobs thoroughly and treated the woorden parts with a liquid wax for fine wood.

The radio is playing very well now. The sound is rather good, better than most of my other radios. This must be attributed to the large speakers. But it tends to distort when the volume is turned higher. And the bass is not really what it should be. This is probably caused by the extremely small ouput transformers. Except for this, I'm very satisfied with this last-generation valve radio.

Copyright © 2004 by Onno's E-page         published 2004-07-03