Pye_TRP-1_review_2008.pdf

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1、Pyo ?PcRRei .10 atuaKAwGfti Despite government opposition, radio communications spread rapidly in Australia following the end of WW2. Released in 1949, the Pye TRP1 was one of the new breed of HF portable transceivers designed to meet the growing demand for suitable equipment. AER, LOAD _CRn. TRANS

2、.REO Po245.14 ! 2 -.- PA. -C:i.;40;, Off ER TUhc MCF( VOLUME 1111 411, This view shows the fully restored transceiver. The original brown cabinet was resprayed a hammertone green colour and looks new again. By RODNEY CHAMPNESS, MUG F OLLOWING THE END of World War 1, many groups pushed for the widesp

3、read adoption of radio commu- nications despite strong government resistance. In Australia, these groups initially included people who were remote from telephones and the tele- graph systems of the day. One pioneer, the Rev. John Flynn oversaw the development of radio communications for what was to

4、become the Royal Flying Doctor Service. The first of his innovative pedal-powered radios came into use in 1929 and used several shortwave frequencies. Fishing trawlers also started using radio communications at about this time. Early radio transceivers were quite bulky but as World War II approached

5、, a number of compact transceivers were developed for the Flying Doc- tor Service, rural fire brigades, small aircraft, fishing vessels, forestry and farming groups, and surveyors and government departments. However, the number of sets produced during this period was not large as the gov- ernment wa

6、s still reluctant to licence radio communications services and placed many obstacles in the way of those wishing to use this medium. In addition, suitable radio trans- ceivers were expensive to produce, were still relatively bulky and were nowhere near as effective as commu- nications equipment is t

7、oday. After being exposed to HF radio communications during WWII, many returned servicemen could see the value of HF communications in peace- time. As a result, radio communica- tions began to rapidly expand in the civilian sector and a number of compa- nies produced suitable equipment to meet the d

8、emand. One such company was Pye-Electronics Pty Ltd, which included Electronic Industries Ltd and Radio Corporation (Astor). The TRP1 transceiver Just prior to WWII, Radio Corpora- 86 ?SILICON CHIP ? .au tion designed and built the RC-16B HF transceiver (and the ATR4A/B military version). This cover

9、ed the 3-7MHz band and had a transmitter output of around 1.5-2W. It was quite effective for its time but its battery drain was quite high, the set consuming around 4W of power on receive and 12W on transmit. It was hardly a lightweight either, with the equipment packs adding up to around 19kg. With

10、 the availability of low- current miniature valves after the war, Pye decided to design and build a replacement for the RC-16B. It would have similar performance to its predecessor but would be considerably lighter and use less power. In addition, its tuning range would be 2.7-7MHz, which is slightl

11、y wider than the tuning range of the RC-16B. The result was a portable HF amplitude modulated (AM) transceiver designated the TRP-1 and released in 1949. This set used a conventional chassis made from Duralium (a lightweight aluminium alloy) and this in turn was housed in an aluminium case to keep t

12、he weight down. Designed for use either as a semi- fixed portable or as a true port- able transceiver, the TRP-1 consumes around 2.6W on receive and around 9W on transmit (considerably less than the RC-16B). Configured as a Walkie-Talkie station, it weighs just 9.5kg and the receiver draws 350mA at

13、1.5V, 14mA at 150V and 0.06mA at -10.5V. As expected, the transmitter draws considerably more, with 540mA at 1.5V, 50mA at 150V and 100-200mA at -10.5V. The portable battery weighs 3.6kg while the larger camp battery weighed in at a massive 16.7kg. Circuit details Fig.1 shows the circuit details. Th

14、e receiver is a conventional superhet with a 1T4 RF stage, a 1R5 converter, a 2-stage IF amplifier using 1T4 valves, a 1S5 detector/AGC/audio amplifier and a 3V4 audio output stage. A bias of -4V is used for the 3V4 and this is obtained directly from a tapping on the -10.5V bias battery. The RF, con

15、verter and the first IF stages all have simple AGC applied to them. The converter can either be manually tuned across the 2.7- 7MHz band or accurately tuned to a spot frequency using a crystal os- cillator. The high tension (HT) for the receiver is supplied by a 150V battery via two parallel 101(Q r

16、esistors. These drop the voltage to around 75V when the receiver is operating. Now lets take a look at the transmit- ter section. As shown, it uses a 3S4 as a crystal oscillator and driver for the output stage. This stage has -4V of bias applied to protect the valve in the event that crystals are no

17、t fitted to all three possible positions (ie, if a vacant position is selected by the frequency switch). The oscillator plate circuit is tuned by C31, C32 or C33 to suit the particular crystal selected by switch S2. The RF output stage consists of two double-triode 3A5 valves, with all sections in p

18、arallel. Each plate is fitted with a 50Q parasitic stopper resistor to prevent spurious signals from being transmitted. With four triodes in parallel, it is mandatory to include a neutralising The cabinet had been knocked about during its life and had quite a few dents and flaking paint. The dents w

19、ere knocked out and the cabinet resprayed green to match an earlier production run (see facing page). circuit. In this case, neutralisation is achieved by feeding back energy in anti-phase via the tapped secondaries of driver coils L5 and L6. The result- ing anti-phase signal is applied via neutrali

20、sing capacitors C27 a 88 ?SILICON CHIP siliconchip.corn.au Although neat, the wiring under the chassis is quite crowded, making some parts difficult to access. The paper capacitors all required replacement. Taken from the handbook, this photo shows the TRP-1 transceiver (centre) complete with all it

21、s accessories, including batteries, antennas and the microphone. The large camp battery at top left was optional JUNE 2008 89 switches the antenna from the receiver to the transmitter, disconnects the receiver filaments and applies 1.5V to the transmitter filaments. Note that the HT is left on at al

22、l times in both the transmitter and the receiver. This means that no work should be done on either the trans- mitter or receiver sections with the set turned on. Restoration As can be seen from the photo- graphs, the cabinet of the unit featured here had been knocked around quite a bit. In fact, the

23、 paint was flaking off and the cabinet had a few dents in it but this is understandable considering the type of work the set did. I knocked out the dents in the case using a small hammer and a heavy flat piece of metal which was placed behind the surface being worked on. That done, the case was clea

24、ned with a turpentine-soaked rag to get rid of any grease and then sanded to remove any loose paint. Next, I covered the rubber grommets and the labels on the cabinet with masking tape and gave the worst areas a coat of spray primer. The first pro- duction run of these sets was painted a green hamme

25、rtone colour but this one, part of a later run, was painted a salmon colour. However, I repainted this unit hammertone green like the null out the grid-to-plate capacitance in the valves (this circuit is similar to that used in the early triode-tuned radio frequency (TRF) receivers). Note that the o

26、utput circuit is manu- ally tuned and the circuit loaded for best output on each transmission frequency selected. The modulator is the essence of simplicity. It consists of a carbon mi- crophone, a -10.5V supply to power the microphone and provide bias for the RF output stage, plus a microphone tran

27、sformer (T5). In operation, speech signals are picked by the microphone and fed to transformer T5. This then modulates the transmitter by applying the audio signal directly to the grids of the 3A5 valves which operate with the full -10.5V of bias. The changeover from receive to transmit is accomplis

28、hed by pressing the press-to-talk (PTT) button on the microphone. This grounds one side of the changeover relay which then .au MANUFACTURED BY AWA in the 1960s, the Radiola Transistor Seven came in quite a few model numbers, each based on a small upgrade.These model numbers included the B19, B19Y, B

29、19Z B24, B24Z 2N1638 first IF amplifier; 2N406 overload; 2N1638 second IF amplifier; 2N408 audio driver; and 2 x 2N408 push-pull audio output stage. The diode detector was a 1N87A. The audio output was just 150mW before noticeable distortion and although this doesnt sound much, it was still very acc

30、eptable. Photo supplied by the Historical Radio Society of Australia Inc (HRSA), PO Box 2283, Mt Waverley, Vic 3149. .au first production run, as I had almost a full can of this relatively expensive paint. In fact, I had previously used it to repaint another communications transceiver (ie, the Harbr

31、os 12/54B featured in October 2005). With the painting completed, I removed all the knobs and cleaned them with warm, soapy water and a nail brush. They were then thoroughly rinsed and allowed to dry before be- ing put back on the set. I also had to remove the receivers tuning-dial for service and t

32、his is done by loosening two screws on the gang shaft. The dial is then slid forward along with the tuning knob and the edge-drive mechanism slipped off the edge of the dial. I cleaned the dial-drive system and then proceeded to carefully reas- semble it. The two pressure washers, which grip on oppo

33、site sides of the dial scale, are under quite some pressure from a coil spring. They took some separating but with perseverance I succeeded in getting them to once again grip the edge of the dial. That done, I reassembled the drive. All of the control shafts were then lightly oiled so that they oper

34、ated smoothly, although none was stiff due to con- gealed oil or grease. Perished battery cable The battery cable had perished rub- ber leads, which could have caused shorts in the set or placed 150V onto the valve filaments with disastrous results. The safest thing to do was to replace this lead en

35、tirely. I removed the 4-core cable from the set, along with its plug. The plug cover was a bit rusty so it was cleaned up and spray-painted matt black. Originally, I intended making up a lead using four strands of heavy hook- up wire but then I remembered that I had some 5-core automotive trailer ca

36、ble. This looks much the same as the original except that it has plastic covered wires inside the sheath. It has five wires so I just ignored the spare and went ahead and wired the lead to the plug and to the set. The wire colours are different to those in the original cable so I had to be careful t

37、hat I didnt wire the 150V HT lead to the 1.5V filament line. However, just to make sure I hadnt made any errors, I removed all the valves and applied power from my power supply. A quick check with a DMM then confirmed that everything was correct. While the valves were out, I sprayed each valve socke

38、t with Inox to clean any corrosion off the socket pins. Fortunately, the chassis was rela- tively clean on both sides and only needed a light dust out with a small paint brush, An air compressor can also be used (with care) for this job. Overhauling the receiver Now that the set and its cabinet had

39、been cleaned up, it was time to overhaul the electronic circuitry. Unfortunately, the parts are difficult to access in some areas, particularly around the transmitter section, but I was eventually able to replace all the paper capacitors. They were all quite leaky, even though it was obvious that th

40、ey had been replaced about 40 years ago. Some of the sub-miniature metal- lised paper capacitors were smaller than my polyester capacitors, so fit- ting new ones wasnt all that easy. One or two resistors had drifted in value and were also replaced. At this stage, with no shorts or other circuit faul

41、ts evident, I applied power to the receiver. It came on immediately with a rush of noise from the speaker. I con- nected it to an antenna and although I couldnt hear many stations (at least not during daylight hours), it appeared to be working just like it had nearly 60 years ago. Next, I decided to

42、 check the align- ment of the various coils. The oscilla- tor coil was slightly out of adjustment at the low-frequency end of the dial and adjusting it brought both the low and high ends of the tuning range back in line with the dial markings. How- ever, the performance dropped off for frequencies a

43、bove 6MHz so I checked the alignment of the RF and antenna coils. At the low-frequency end, they were slightly out of adjustment and I corrected them by adjusting the core slugs at around 2.8MHz. Conversely, at the high-frequency end of the dial, I found that the per- 90 ?SILICON CHIP ?siliconchip.

44、corn. au This close-up view shows the front panel controls on the fully-restored unit. It tunes the frequency range from 2.7-7MHz and has a transmitter power output of between 1.5W and 2.3W. formance improved if I placed a piece of insulated rod near the RF coil. Un- fortunately, I couldnt adjust th

45、e wire trimmer due its awkward position in the set so I soldered an adjustable trimmer across it and adjusted this for best performance instead. The receivers performance was now quite good, with a fairly even noise level from the speaker across the whole 2.7-7MHz band. The set was also working well

46、 in the Pack frequency position. In this position, a crystal is switched into the converter circuit and the set will only tune to the frequency of the crystal minus the IF frequency (455kHz). However, the manual tuning control is quite critical to set in this mode, Note that the set can also be tune

47、d quite easily to an image frequency, ie, to a frequency 910kHz higher than the desired frequency. I fitted a 3247kHz crystal into the holder and the set now tunes on crystal control to 2792kHz (3247kHz - 455kHz), or to the image at 3702kHz (3247kHz + 455kHz). I se- lected this particular crystal fr

48、equency because the set came equipped with a 2792kHz crystal in the transmitter. Overhauling the transmitter There was only one paper capacitor fitted to the transmitter section and this was replaced with a polyester type. The remaining capacitors are all mica types and were in good con- dition. I e

49、xamined the wiring carefully and could see no signs of any short circuits or other problems. However, its not easy to trace the wiring in the transmitter and I could only hope that there were no nasty faults deep down in the jungle of wiring near the RF output stages in particular. Of course, if there were any shorts on the HT line, this would have shown up as soon as I applied power to the receiver earlier on. With this in mind, I applied power to the transmitter stages and all appeared normal. Both valve stages have protective bias applied.