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VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG The Intriguing Philips “Philetta” Every so often, a radio appears that is quite different from the usual fare of vintage radio receivers. The Philips “Philetta” is one such set. It was not only a multi-band AM receiver but also came complete with an FM band. The Philips Philetta fits into the mantle set category but it’s the inclusion of FM that really got my attention. It is not a large set and has only four valves but despite this, it still delivers good performance on FM (more on that later). Unfortunately, I don’t own this set; Geoff, its owner lent it to me so that I could share this story with you. I first saw this set playing at a vintage radio club meet­ing and was immediately attracted to it. But what really im­pressed me was that it was receiving the local FM stations on just a few metres of wire – and it used only four valves! I just had to have a much closer look at this set and Geoff agreed that I could take it home for a couple of weeks so that I could examine it at my leisure. The Philetta is a small-to-medium The Philetta is housed in an attractive veneered plywood cabinet and is very nicely made. There’s just one problem – it isn’t mine! 78  Silicon Chip sized set in an attrac­tive veneered plywood cabinet. It features a recessed front panel and escutcheon, which means that it can be tipped onto its front without damaging the controls. It really is quite attractive and the wooden cabinet would have been considered unusual in Austra­lia at the time, as most of our sets were residing in plastic cabinets. However, this set is a quality receiver with lots of worthwhile features. Having admired it, I proceeded to put it through its paces. The front panel escutcheon is labelled in German, as is the back panel, but the function of each control is still quite apparent. This leads me to suspect that it was brought into Australia by a migrant during the 1960s. Eventually, it was sold to a secondhand dealer because it didn’t work at times. Geoff bought it from the dealer and quickly found a dry solder joint on the mains switch. The various radio bands that the set operates on are se­lected using a bank of piano-style switches in the lower centre of the front panel. These are as follows: LW (Long Wave) 150-270kHz; MW (Medium Wave), 515-1630kHz; KW (Short Wave) 5.8-12.4MHz; and UKW (Frequency Modulation) 88107MHz. However, the dial calibrations show slightly different tuning ranges, indicat­ing that it was probably tweaked to work on our bands out here, particularly the FM band which shows 88-104MHz. The last switch is marked AUS which means power off. Press­ing LW and KW at the same time actuates the record player termi­nals. The two front panel rotary controls are actually dual con­centric controls. The lefthand one is for volume and tone, while the one on the right consists of two tuning controls – one for the AM bands and the other P.C.B. Makers ! • • • • • • • • The rear panel is well-labelled – even if it is in German! Fortunately, the symbols make it easy to work out what’s what. The back is removed by undoing just two screws, while another four screws underneath release the chassis. exclusively for the FM band. This means that it is possible to set both a favourite AM station and a favourite FM station and just switch between them by pressing the appropriate band change switch. Nifty! Performance Having worked out the function of each control, I soon had it up and running on the AM broadcast band. On local stations, I found that it work­ ed quite satisfactorily using only its ferrite rod antenna. When an external antenna and earth were connected, it proved to be quite a performer, with 10µV signals being heard. On the long-wave band, the set was just as sensitive with an exter­nal antenna connected but didn’t pick up much using just the ferrite rod antenna. A number of non-directional beacons (NDBs) were heard over quite some distance with the antenna connected but unless you are able to read Morse code, it is difficult to determine what the callsigns are or where the stations are locat­ed. On the shortwave band, the results were not as impressive, the sensitivity varying between 30µV and 300µV across the band. Perhaps the alignment was out on this band but it wasn’t my set, so I didn’t have the right to fiddle. Still, the band provided some worthwhile listening – Radio Australia booms in here, being only 10km away, just north of Shepparton. FM performance Now to the FM band. I was curious to find out how well a 4-valve FM receiver would work. For the FM band, there are two sockets for a balanced antenna of 240 ohms – not 300 ohms as generally specified in Australia. The difference in impedance is not important and an FM antenna with a 300-ohm twin lead will work very well with the set. The receiver was connected to just a few metres of wire initially and later to my outside FM antenna. It proved to be quite sensitive on the FM band and all the local stations were received at good strength, along with a few more distant sta­tions. One handy little item at the lefthand end of the escutcheon is a bar-type magic eye valve. This is used for tuning the set for maximum signal strength and works on both AM and FM. I was most impressed with the audio quality of the set, this being noticeably better than from Australian-made plastic mantle sets of the same era. The speaker was around 150 x 100mm and remarkably well baffled for such a small set. The output transformer uses “C” core construction and is obviously a good-quality If you need: P.C.B. High Speed Drill 3M Scotchmark Laser Labels P.C.B. 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Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 ALL MAJOR CREDIT CARDS ACCEPTED Truscott’s • RESELLER FOR MAJOR KIT RETAILERS • PROTOTYPING EQUIPMENT • COMPLETE CB RADIO SUPPLY HOUSE • TV ANTENNA ON SPECIAL (DIGITAL READY) • LARGE RANGE OF ELECTRONIC COMPONENTS Professional Mail Order Service Truscott’s Amidon Stockist ELECTRONIC WORLD Pty Ltd ACN 069 935 397 Ph (03) 9723 3860 Fax (03) 9725 9443 27 The Mall, South Croydon, Vic 3136 (Melway Map 50 G7) email: truscott<at>acepia.net.au www.electronicworld.aus.as November 2000  79 There’s quite a lot of circuitry built onto the chassis – not surprising considering the AM & FM bands that the set covers. Most of the parts, including all the valves and the tuning gang, are mounted on a large PC board. unit, as there is plenty of bass and treble in the audio output. In short, it sounded good. A look inside My next step was to take the back off and remove the chas­sis, so that I could get a really good look at the works. Undoing two screws allows the back to be removed and this reveals a chassis with a PC board that holds most of the parts. The chassis is then released by undoing four screws underneath the cabinet, after which it can be removed by tilting the back up and sliding it out. It comes out with all the controls and the escut­cheon attached. Good one Mr Philips – it’s a pity that a lot more sets aren’t like this as it make alignment so much easier. Another nice feature is that the speaker remains in the cabinet but the red and white leads running to it are long enough to permit the removal of the chassis while leaving the speaker connected so that the set can still be operated. Because the set is able to tune three AM bands and one FM band, there’s quite a lot of circuitry. As a result, it wouldn’t be easy to service without 80  Silicon Chip a circuit diagram but unfortunately, this isn’t included with the set. As shown in the photos, the parts are all mounted on pheno­ l ic PC board. One drawback with this board is that you cannot see the tracks from the component side when you hold it up to the light. This makes it harder to trace circuit paths, although the board appears to be of good quality. On a similar theme, the wave-change switches are all enclosed, so it’s not easy to work out the switch connections from the copper side of the PC board. Circuit technicalities A quick look around the set soon revealed the valve comple­ment. For the AM bands, there’s a 6AJ8/ECH81 converter (arguably the best AM converter of its type), a 6DC8/EBF89 460 kHz IF amplifier and detector, and a 6GW8/ECL86 2-stage audio amplifier. The tuning indicator is an 6FG6/EM84 and is used on both the AM and FM bands. The FM section uses an ECC85/6AQ8 twin triode in the front end, the first triode wired as an RF amplifier and the second as a self-oscillating converter. The output from the converter is nominally on 10.7MHz. By the way, the much higher IF used for FM as compared to AM (455kHz) serves two purposes: (1) it means that “double-spot­ting” is unlikely to occur, as the image is 21.4 MHz away (com­pared to just 910kHz in an AM receiver); and (2) it provides the necessary bandwidth (180kHz) to receive the FM signal without clipping the higher amplitude (ie, louder) audio signals. Following the 6AQ8, the signal is applied to the 6AJ8 con­verter valve. In this case, however, it is configured to act purely as a 10.7MHz IF amplifier and its output is applied to the 6DC8 which acts as the second IF amplifier. From there, it goes to a pair of germanium diodes connected in a frequency discrimi­nator circuit. Finally, the detected audio is fed to the 6GW8 audio output stages, as in the AM mode. The FM IF has no limiting circuitry and there is no inter-station muting – two features that are commonly found on later sets with FM tuners. Power supply The power supply is quite conventional and uses a trans­former with a tapped primary for 110-127V and 220V AC. In Austra­lia, the receiver has 240V AC applied to it, so it is being operated above its rated mains voltage. Despite that, it has worked well for many years without any problems or signs of overheating, so it can obviously tolerate this situation. The high-voltage AC output from the transformer is fed to a block selenium rectifier which uses the chassis as a heatsink. This gives an output voltage of about 245V DC, so with 220V AC mains the output would be about 225V DC. Ancillary circuits The tuning indicator is mounted upside down at the left front of the set and is held in place with a close-fitting metal sleeve. As a result, the valve socket that the indicator plugs into is “floating”, with the leads running away to the PC board. It’s quite safe but is rather unusual since we are used to valve sockets being firmly attached to the receiver chassis. On the back of the chassis are two DIN sockets, one for a record player input and the other an output for a tape recorder. Certainly very little has been left to chance in this little set. Safety blemish From all the foregoing, it might be thought that I think this set is without blemish. Not so! European receivers often have mains wiring exposed when the chassis is removed from the cabinet, often just where you might be tempted to place your hand to turn the set over! This set is not as bad as some but the power transformer terminals are exposed along one edge of the chassis. Repositioning these deadly termi- The PC board assembly is quite well-made, although it is rather difficult to determine which tracks go to the components mounted on the top of the board. This makes signal tracing rather difficult and this would not be an easy set to service without a circuit diagram. nals or at least putting a cover over them would not have been all that difficult. Another small problem is the effect that the heat from the output valve has on the cabinet above it. It has caused the veneer to split slightly. Including some method to dissipate the heat above the audio valve would have eliminated this problem. Summary As you will have gathered, I was very impressed with this little mantle receiver. In my opinion, it’s the best European-made set that I have seen. That’s not to say that it has the best performance, looks the most elegant or has the most features. It was, after all, designed as a medium-quality receiver that could be sold for a relatively low price. It has a nice cabinet, is easy to disassemble, works well and has most of the frequency ranges that were (and still are) used in Europe. However, at the time this set was brought to Australia, we did not use the FM band for domestic radio broad­casting. The same goes for the long-wave band. What failings does the set have? Well, we mentioned the lack of a circuit diagram, the exposed mains terminals and the heat damage to the top of the cabinet. That said, I have been quite picky about the faults and had to look hard to find any. The only real problem I have with this set is that it isn’t mine. If you see one, grab it; it’s worth collecting. SC DON’T MISS THE ’BUS! Do you feel left behind by the latest advances in com­puter hardware and software? Looking for an easy-to-read book that explains the technology. Don’t miss the bus: get the ’bus! Includes articles on troubleshooting your PC, installing and setting up computer networks, hard disk drive upgrades, clean installing Windows 98, CPU upgrades, a basic introduction to Linux plus much more. 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