[SeanStevens]

This RP25 was possibly the filthiest radio I’ve found to date. It was grey! Although Hacker made it originally in blue. After a long session of cleaning (washing up liquid, hot water and lots of scrubbing) the colour returned and it was clean enough to handle without further hazard to health! Unfortunately, no ‘before’ photo was taken.

I threw in two PP9’s and was rewarded by spectacular motorboating – the likes of which I’ve never heard before. Not only was all the audio going ‘pop pop’ but there was a screaming high pitched noise to accompany it. Truly horrid.

I tested the battery voltages on load and found that one of the batteries was very low (5v), so I found a replacement. Motorboating was still all there was to hear – no matter what band chosen. After cleaning the umbilical cord connections to the amp, similar sounds, possibly a bit faster! It was time to take it to see Ian.

Oddly, FM worked when it arrived at Ian’s. No LW or MW though. There was one electrolytic capacitor standing on the RF Oscillator board (C21 – 350uF) that when tested had a very high ESR (>10 ohms) the replacement I compared it to had almost zero ESR.

It was an odd capacitor, as normally the body of the cap is negative (the can). This one however was all red and had a wire leading up the side to black section on the top. This was obviously the negative and the entire red plastic body of the can was the positive (had a little wire hanging out the bottom of the encapsulation). It was enough to confuse me – but it seems a silly mistake to have made now. Once this cap was changed the motorboat was a distant memory, however, there was nothing but hiss – no signals could be heard.

Using a sig-gen and fed into the workshop aerial a 470 kHz signal was broadcast close to the radio – this came through perfectly. Ian, being well ahead of me on the diagnostics front, suspected the main oscillator. With a little maths we added a known MW station frequency to the IF 470 KHz and got something around 1163 kHz (693 + 470kHz) With the sig-gen set to this and fed into the workshop aerial, the radio could now be tuned to a strong local MW station. So – no local oscillator!

TR1 (oscillator) was found to be a lock-fit BF194 and had no voltage on its emitter– when removed and tested on a PEAK component tester it did not appear as a component at all! Ian suggested a replacement of a different type (BF180) – this made my fragile mind spin out entirely, as it had four legs and not three. Once I’d found the E, C, B trio I had terrible trouble getting it orientated into the radio. For some reason, the board had almost all transistors marked up with E, C, B – but not TR1 – Again I got lost and had to be shepherded back into the game by Ian. There were some obvious connections from the transistor base to resistors and one to a coil; this helped me identify the orientation – again, with help. With the BF108 in the radio instantly sounded promising and once tuned to a broadcast, sounded truly marvellous. LW R4 sounded as clean as FM R4 – a trick a decent Hacker or Roberts makes look easy.

SEAN