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Thread: Leak Troughline Stereo Tuner service/repair

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    Default Leak Troughline Stereo Tuner service/repair

    Today I drove to Malvern from London to see Mark the Ming (Mark Mainwaring White ) who is Ming Da UK. Though having played with valves since he was a boy Mark repairs any make of valve equipment. The reason for the trip was my Leak Troughline Stereo receiver which is connected to a Tim de Paravicini MPX decoder ie it had stopped working.

    It transpired that a copper wire inductor had moved causing it to short out, the trip had already been anticipated as the sensitivity of the tuner had been dropping off over time & the AFC & best reception had got out of sync.

    I had read on line that the FM discriminator T4 in the Troughline containing germainium OA79 diodes which could be to blame. initially they appeared to be made of unobtainium perseverance prevailed, I found some @ 8 plus postage some on fleabay that were used and out of spec according to quoted figures, I then saw an add for Littlediode of Malden Greater Londonon the bay two cost under 8 posted I asked if I could have a matched pair I therefore went to Mark prepared.

    Mark found as I watched that both OA79 germanium diodes had drifted more than 25% off so had the associated resistors. A bit of soldering later then connecting the required oscilloscope and signal generator together with judicious tweaking of the 3 double ended potentiometers.

    The result was absolutely stunning.

    Photo of T4...

    Last edited by Big John; 29th October 2015 at 23:08. Reason: Photo added

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