On this site:

Philips B7X14A radio (1961)

Around 1961, the B7X14A was the top model from the "Plano" range. The "Plano" models were rather flat models, with the speakers on the sides. This is a luxury model with 10 valves. It has a posh mahogany veneered case with a thick, high-gloss varnish. The gold and brown tuning dial must have looked impressive at the time but it looks a bit ridiculous now. Even more outdated is the reverberation unit that "enhances" the sound to produce a sort of spatial stereo. It has a good sound though, due to the large speakers. But before I could listen to it, I had a lot of work to do...

This is one of the many "Plano" that Philips produced from the mid-fities until the mid-sixties. The "Plano" models were compactly built, rather low and wide models, usually having the speakers on the sides. They were usually mid-range to high-range models. They were modern, a departure from the luxury models from the fifties, that were tall and bulky radios with front speakers. The "Plano" form factor was handy for stereo radios. Putting the speakers on the sides was a natural thing to do for a stereo radio if you didn't want to separate the speakers from the radio. This model, the B7X14A, was a luxury model from around 1961. It does have a stereo amplifier, but no FM stereo reception yet. In Holland, FM stereo broadcast started in 1963 and Philips did not include the stereo decoders in regular models before that time. Instead, this radio has a reverberation unit to get a more spatial sound. This does sound impressive at first, but one gets tired of it quite soon.

I got this B7X14A radio for free, without valves. The man who gave it away told me the FM range did not work and the sound on AM was bad. That was before he had pulled all the valves. But I was quite confident I could replace the valves and make the radio play again. It needs 10 valves: 2 EL84 AF output amplifiers, an ECC83 AF pre-amplifier, an EAA91 as FM detector, an EBF 89 as third FM IF and AM detector, an EF89 as AM IF amplifier and second FM IF, an ECH81 as AM frequency changer or FM first IF, an ECC85 as FM RF amplifier and frequency changer. There also is an EM80 tuning indicator and a heavy-duty EZ81 rectifier.

I almost fried the mains transformer when I first tried the radio using a bad EZ81 with a short circuit. But the transformer survived. When all the valves were in place, the AM wave bands worked again. FM was mostly dead, though. It seemed that the oscillator in the FM front end wasn't working. Swapping the ECC85 valve did not make much difference. I noticed the radio was quite dirty: there was a dry layer on the frame and some greasy goo in the ECC85's socket (contact grease?). I suspected the FM front stage, opened it and cleaned the valve socket and the tuning inductors. That did it! It worked again.

The sound was distorted, though. I found all stations on two locations close apart. There was much distortion on the point where the tuning indicator indicated the strongest signal. The point where you got the best sound was slightly off that position. It looked like the FM IF or the FM detector (or both) were out of alignment.

Before I started messing around with the IF transformers, I wanted to be absolutely certain that they were misaliged. I used an RF generator and scope to plot the detector curve and found it gave a very odd picture. Slightly confused and doubting whether I had done the measurements right, I decided I had to confirm these measurements by testing another similar radio. On a flea market I found the radio's little brother, the B5X14A, that uses a similar chassis but with a number of minor differences, such as a lower plate voltage, smaller speakers and no silly reverbeo unit. I tested the B5X14A and found the results were just as I expected. A nice S shaped detector curve with the middle of the «S» almost exactly aligned with the strongest signal level. In other words: something nasty had happened to the B7X14A. It may have been exposed to high temperatures and/or greasy pollution.

Realigning the detector or the IF stages wasn't easy, though. Whatever I tried, the cores were stuck. After I broke the ratio detector transformer, I did not dare to continue. Fortunately, these coils are not too rare. Through the Dutch Forum on old radios I found a new one. I used a special oil to lubricate the other cores, which helped with most of them.

But I had to accept some compromises when I tried alignment again. Not all of the cores could be set, so I made an alignment that gives a reasonably symmetrical detector curve but a somewhat wide IF bandwidth. I decided to stop working on it for a while. I was satisfied by its sound, though it was not as selective as it could be. I finished the work by cleaning the knobs and frame.

After all this, the radio looked fine. AM reception good, FM reception reasonable. I used it in my study for a while. And though I thought I'd keep it forever, I let go of it when someone offered me to trade it for another stereo plano, a B8X44A with full FM range and stereo decoder.

Copyright © 2003, 2004 by Onno's E-page         published 2003-12-14, last updated 2004-07-03