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Thread: A-100 Percussion issue, Leslie motor issue, and any techs in Vancouver BC?

  1. #21
    ppp Pianississmo funkyhammond's Avatar
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    When I click on the link in the safety thread it says the wiki is down for maintenance. I'm having trouble finding the discharge info I need by searching the forum, so I'll wait and hopefully the wiki will be back up sometime soon. Regardless of the discharge instructions, I am also wondering if there is a totally reliable amount of time to wait where you are guaranteed the capacitor has self-discharged.

  2. #22
    fff Fortississimo geoelectro's Avatar
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    1 members found this post helpful.
    In a properly working amp, the voltages will discharge in seconds to a safe level. However, if there is a problem, depending on what the problem is, it could take longer. Also, if you power up a working amp, but turn it off before the tubes warm up, it cannot discharge.

    The discharge path is the tubes. The output tubes specifically discharge the power supply quickly if they are at operating temperature. So powering an amp up with the output tubes removed also removes the primary discharge path for the power supply. I was shocked from an amp that had an open output transformer. The path of discharge in that case was broken.

    The best way is to measure the voltage to be certain. You can take a resistor and touch it to ground and each of the terminals on the filter cap. The discharge rate will depend on the resistor value. The smaller the value, the higher the wattage. For example, a 100 ohm will discharge fairly quickly but may overheat unless it’s a higher wattage. A 2 watt for example.

    Geo

  3. #23
    ppp Pianississmo funkyhammond's Avatar
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    Thanks Geo. I have seen some videos on youtube showing that technique on filter caps of guitar amps. I'm still unclear as to what the safest procedure is to access the terminals of the can capacitor in the leslie amp. Are any other capacitors inside the Leslie amp anything to worry about in terms of safety?

  4. #24
    fff Fortississimo geoelectro's Avatar
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    The filter cap is a large can with 4 terminals. Flip the chassis over, put your resistor on each terminal one at a time until drained. Or, for a few minutes. You can just ground the terminals if they are drained or close to being drained.

    No other caps are a concern. Just the filter can.

    Geo

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