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Warbly tones = broken TW filter (delaminated)

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  • Warbly tones = broken TW filter (delaminated)

    Working on the AV generator.

    I had a really freaky acting note in the generator - #55. Its volume was fluctuating, the waveform was funny looking on the scope, and if you knocked on the generator chassis (anywhere) It showed up on the scope as amplitude fluctuations. For a long time I thought the pickup was somehow loose so I spent a LONG time checking that over - until I discovered that if I pressed down on the filter coil (or indeed on the filter tray close to the #55 coil) the situation stabilized and the sine shape came back on the scope. Also, any movement of the generator frame... such as lifting ever so slightly at one corner, for instance - also showed up on the scope.

    So I take the filter out, and realise the metal "core" has delaminated and the core segments are loose, moving around freely when touched. I proceeded to check all the filters and found 3 more that exhibited the same problem, if not as pronounced.

    Ok, out to the garage and rob same filters (#49,55,56,57) from an old scrapped M-100 generator. Rewire them slightly so as to match the layout of the generator without splicing the stock TG wiring. And - hey presto, all is well again (at least for 55 and 57 which were the only two I had the time to complete last night).

    I have never heard about this particular failure mode before, but now that I know it exists I realise it might actually be a common cause of "warble" phenomena. But a cause nobody thinks of.

    Anyone in the group experience the same thing?
    Current organs: AV, M-3, A-100
    Current Leslies: 22H, 122, 770

  • #2
    Nice find enor. I don't recall this being discussed on any Hammond forum I've participated in. Having a random variable inductor will certainly mess up the filter.



    • #3
      As there was nothing to lose, I'd have hit the thing with some thin superglue to stabilize it and see if that worked OK.


      • #4
        Great post, Magnus. That's a new one on me!