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Old 6th Dec 2018, 10:29 pm   #1
martin.m
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Join Date: Mar 2018
Location: Bishop Auckland, County Durham, UK.
Posts: 373
Default Hacker VHF Herald RP37 repair

This is my first Hacker repair. I bought the radio untested and after a quick visual examination I switched on then connected the batteries. There was a "plop" from the speaker but no sound. A meter in series with the supply registered a current of 0.5 amps (my present multimeter has seen better days and only works on the 10 amp range). Time to switch off. Repeating the test with the speaker unplugged gave a reading of around 20mA. Out came the audio panel and a few cold checks revealed that a 400uF 10v cap in series with the speaker was short circuit. A replacement 470uF 25v was fitted and this restored sound but the radio burst into positive feedback when the Bass control was advanced. I decided to change the other electrolytics on the panel apart from a blue Philips 125uF and this cleared the instability. I will set up the quiescent current and mid point voltage when I get a new multimeter.

Next problem was the volume control. Not the usual crackling but the sound went off completely if the volume was altered even slightly. I removed and dismantled the control which was full of oily black gunge. Cleaning and careful bending of the rotor contacts followed by a little lubrication cleared the intermittent sound.

I noticed that the frequency coverage wasn't quite right. I couldn't tune in Radio 2 on 88.5 MHz, the local station BBC Tees on 95 MHz appeared at 93 on the tuning scale, while at the top end it was possible to receive BBC Radio York on 104.3 MHz. The set is only supposed to go up to 101 MHZ. There is a brass tuning slug visible on the screened tuner module marked "osc". I don't usually like disturbing any alignment controls but as an experiment switched off and rotated the slug exactly one turn clockwise. This enabled Radio 2 to be tuned in and BBC Tees (95 MHz) appeared at 94.5 on the tuning scale. Classic FM could still be received around the 100 mark so I decided to leave well alone until I know what I'm doing. Perhaps someone had tweaked the control to extend the frequency coverage.

Cosmetically the Herald was in fair condition and responded well to a clean and polish. Unfortunately the gold coloured metal surrounds on the control knobs have suffered a little corrosion probably due to damp and the rear plastic grill is missing.

This model looks very smart in red with gold trim and has a lovely sound. I would like to get one with the Elac speaker eventually.
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Martin

Last edited by martin.m; 6th Dec 2018 at 10:31 pm. Reason: spelling
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