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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 15th Feb 2018, 10:02 pm   #1
Brettski
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Default Hacker RP25 project

I have finally dipped my toes into the the Hacker brand with two RP25s. One dead and missing bits and one working (of sorts) with good grilles and Aerial .

I have read the threads on here and elsewhere on the net in the search for answers and I think I’ve identified my issue.

I have good reception on all bands, but once the volume is raised past around half I lose the volume and get distortion especially on strong stations. It’s almost as if the batteries can’t cope, but they are a new pair.

I’m guessing the amp board is failing . Is there anything I can do before I look at either attempting repairs myself or asking some one to rebuid the board for me?

I could always take the board out of the non working set and try that. I could always attempt a rebuild on this board, I reckon I could replace the caps , but not sure about the transistors so it might be better to have some one rebuild this .
Brett.
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Old 15th Feb 2018, 10:49 pm   #2
wireless_john
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Default Re: RP25 project

I have had faulty electrolytics and dry/cracked joints and tracks around the connector pins on these boards.
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Old 15th Feb 2018, 11:05 pm   #3
mhennessy
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Default Re: RP25 project

The blue Philips and grey Japanese electrolytics fitted to these were generally pretty good, but occasionally you find some of their older stocks of blue DALY or red ELKOMOLDs.

My first step here would be to put a voltmeter across the 18V supply and satisfy myself that the supply isn't falling under load.

Do also bear in mind that no radio is designed to have the volume turned up all the way without distortion - they always have "gain in hand" for the very quiet bits of a broadcast, but that means modern broadcasts (which are fully modulated) will cause the amplifier to distort well before full volume. If you have one, a 'scope across the output is useful - then you can check that you're getting something close to 18V peak-to-peak when the distortion sets in.

Also, loudspeakers can distort. The Celestion units often fitted to these are very prone to "cone sag", which is sometimes more problematic at higher volumes.

The 5 pin connector usually causes low frequency motorboating, but other symptoms are possible, so checking that out is never time wasted IMHO.

Good luck,

Mark
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Old 16th Feb 2018, 10:55 am   #4
Brettski
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Default Re: RP25 project

Thanks Mark. Maybe me description of the fault was perhaps a bit wishy washy. After half volume the sound seems to drop out especially on modern dance music stations, along with the beat as it were, if that makes any sense. I have had the plug off the board and fiberglass pencilled the pins, deoxit and put back together. Still no joy.

I will keep at it. I think I will try the board from the dead set next.

Brett.
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