Fullscreen HTML5Med Res (??MB)HTML4

VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG An Australian-made 6-transistor personal portable Yes, early transistor radios are now vintage and are worth restoring. One such receiver is the Kriesler 41-32, an Australian-made 6-transistor “pocket” radio that was first made in 1962. Transistor radios started to become readily available (at a price) in the mid to late 1950s. Initially, their performance left much to be desired. However, the general public was prepared to accept performance that was inferior to the good valve portables of the time in favour of a set that was relatively compact, light and portable. Another factor in favour of the transistor radio was that it operated from low voltage batteries at low current drain and so was cheap to run. In city areas, the problems of poor sensitivity and noisy operation (due to limitations in the transistors) were of little consequence as the stations were strong. In many ways, it was a blessing in disguise that the sen­sitivity was poor. The overload characteristics of these sets and the transistors they used were, to put it mildly, terrible. Imported sets Very few radios were imported into Australia until the commencement of the transistor era over 30 years ago. Australian-made valve radio were as good as any and there was no need to import sets from elsewhere. However, transistor sets started to come in from Asia in increasing numbers from that time. Initially, some early Australian transistor sets used point to point wir- ing, as was used in most valve radios. By contrast, the Japanese sets used PC boards right from the beginning in all the sets imported here. Transistorised radios lent themselves very much to the use of PC boards. Transistors could be wired in much the same way as resistors and capacitors and all the coils had become miniaturised by that time too. As a result, this type of construction became the standard within a very short time. The PC board method imposed difficulties for servicemen, however – particularly when they had to service Japanese pocket sets. Everything was crammed in, it was difficult to trace the circuit and the type numbers of transistors, etc, were unknown to Australians. As a result, it was difficult to do much with them if something went wrong. By contrast, many of the Australian manufacturers laid their boards out with more space between components and they often printed the track pattern on top of the board to aid cir­cuit Fig.1: the circuit of the Kriesler 41-32. It used six transistors, all germanium PNP types. August 1998  85 The Kriesler 41-32 was typical of transistor sets built in the early 1960s. It featured a “handspan” dial and a cabinet made from plastic and vinyl. Although described as a “pocket radio”, quite a large pocket would be required to carry it. tracing. This made it much easier when the set required repairs. One of the bugbears of servicing or restoration is disman­tling the sets to work on them. Some sets are easy to dismantle and reassemble while others are a nightmare. Regrettably, many transistor sets were horrors to work on and, as a result, were consigned to the rubbish bin before many older valve sets! The Kriesler 41-32 The Kriesler 41-32 was put into production in 1962 and is a typical Australian made 6-transistor pocket radio. A large coat pocket would be needed to carry it though. It is quite a reasonable performer, being considerably better than the first 6-transistor sets that came onto the Aus­tralian market. It used the later PNP germanium transistors in the RF and IF sections – namely the OC170 and OC169 transistors – instead of the OC44 and OC45 types used in the first Australian transistor radios. A larger than normal ferrite loopstick aerial was also used to improve the performance. The set doesn’t compare favourably 86  Silicon Chip with transistor porta­bles that have an RF stage, however. It wasn’t meant to be used in other than suburbia and, in this role, it does the job quite well. Inside the set The photograph of the back of the set shows that it used both full-size and miniature components. The tuning gang is full size, as is the trimmer capacitor and the on-off volume control. A circuit diagram was pasted onto the back of the set, which was a good idea. The circuit is relatively simple and has both voltages and currents marked on it. This helps to make servicing easier. The set uses PNP germanium transistors throughout. I don’t know about others but I find that working with PNP transistors requires some mental gymnastics for me to remember that the collector (equivalent to the plate of a valve) is negative with respect to the chassis or emitter (cathode in a valve). NPN transistors work the other way around and the voltages are like the convention we got used to with valves. Having said all that, how easy is the set to dismantle and keep operational whilst doing the service work? Not at all easy as it turns out. There are three screws and one nut to undo (as shown by the white arrows on the photo) and then the PC board can be lifted up after unclipping it at the righthand end of the cabinet. The disassembly notes in the set say “lift board from cabinet to limit of the leads”. This is fine as far as it goes but the board can’t be worked on in this condition, as the leads are not long enough to give easy access to both sides. With a little more thought it could have been made a dream to work on. If the board had been made so that it hinged at the end nearest the tuning gang, the tuned circuit leads would not have to move much at all. At the righthand end is the audio section and the leads could have been longer and dressed so that the board could swing out at right angles to the cabinet. It would then act as a prop to stop the set falling over and service would have been a breeze under these circumstances. It wouldn’t be all that difficult to modify the lead dress to accomplish most of this but it is always harder to do as a modification after manufacture. In the process of overhauling this set I ran into a real problem. The tuning gang had both sections shorting at various spots across the dial. I tried bending the moving plates with it in situ but couldn’t get it so that no shorts were occurring. It had to come out but how could that be done? It was not possible to gain easy access to the screws hold­ ing the gang onto its mounting plate, as they were behind the aluminium front The Kriesler 41-32 used a mixture of full-size and miniature components, the full-size mounting plate. In the end, parts including the tuning gang, the trimmer capacitor and the combined on-off/volume the whole set had to be discontrol. The PC board can be lifted clear from the case by removing three screws and mantled and I ended up with one nut, as indicated by the cardboard arrows. a collection of parts on the workbench, all held together troublesome easing the gang assembly glue to lock several screws into posiby a few pieces of wire. out of the set. tion into the plastic front escutcheon I decided to remove the dial scale (several had come loose and it made After that short story on how to on the front of the set as it would need it hard to tighten the nuts on them). cleaning. After prising the retaining remove a gang, I’ll get on with how clips away from the plastic dial scale, I fixed it. After a lot of mucking Several other parts on the front of the set had to be glued as well. around, the plates were bent so that it came away. The retaining clips were Cleaning the vinyl is a problem as on a circular plastic plate mounted no shorts occurred at any position of with three screws to the front of the the gang. This was confirmed using a even soap and water causes the paint multi­meter. on it to come off and the set then looks set. Removing this plate revealed two a bit weather beaten. It’s a matter of It appears that in the past, someone large holes through which I could have gained access to the gang mount- slipped with a screw­driver or some cleaning it and have some of the paint other tool when working on the set on the vinyl come off or leave it dirty. ing screws! This would have saved me native is particularly and actually damaged the gang. Hav- Neither alter­ quite some time if I had known this ing fixed that, the set was a goer and impressive. As a result, these sets beforehand. cannot be made into beautiful pieces after touching up the alignment, it Kriesler’s method of furniture like the wooden con­soles performed quite well. Batteries are a problem for many of often are. The Kriesler Technical Service Information does describe a technique these sets as specials were made for Summary quite a few brands and models. This for removing the works in such a way set used a small 9V battery called a So there it is – an old “pocket” as to have the set still operational. To do this you remove the tuning knob, 2362 which is no longer available (and 6-transistor radio of Australian manwhich would probably be expensive ufacture. It’s a reasonable performer remove the three nuts securing the if it was). So what could be used in and although it can’t be made to look aluminium gang bracket to the front a million dollars, it’s worth re­storing escutcheon and release the board from its place? because of the era it represents. It would have been nice to use six the bracket on the speaker end of the penlite cells but a pack is just too One question that remains is where receiver. The board, complete with gang, big to fit in. The only alternative is do you get transistors if they are ever a 216 which will fit in but with a needed for replacement purposes? volume control and loopstick antenna current drain varying between 10mA Germanium PNP transistors are availcan then be lifted clear to the limit of and 40mA, it won’t last long. One of able from time to time at flea markets, the speaker leads. Unfortunately, they the heavy-duty alkaline types may etc, but they are not as easily obtained missed out on telling servicemen to remove one nut in the centre of the be worth considering if the set is to as valves. In some circum­stances silibe used for entertain­ment as well as con PNP transistors can be used if the circuit board. operating conditions are changed to Yes, this will work although in my being a vintage radio exhibit. suit. The forward bias required for a opinion the method I described earlier Cabinet problems germanium transistor to conduct is is much better. Even so, if I’d had this about 0.2V but for a silicon transistor, The plastic and vinyl components infor­mation earlier, I might have got the set to pieces with less trouble. The of the cabinet were in fairly ordinary it is about 0.6V. This issue will have to be explored screw threads seemed to bind to the condition, which is now normal for SC aluminium and the nylon and it was these sets. I used some form of super- in depth at a later time. August 1998  87