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Thread: Moist Filter Caps?

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    Moist Filter Caps?

    I built a single channel 50 watt fender style from a bassman head that was damaged in a fire. I reused the filter caps and all seemed fine until the amp sat unused for about a week. There is now a strange distortion that seems to decrease the longer the amp is played. I just wonder if the dousing the filter caps got from the fire hose has caused them to retain moisture. The caps are Sprague Atoms that were installed in the amp about a year before the fire. Anyone have any experience with "wet" electrolytics?

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    Quote Originally Posted by jvm View Post
    I built a single channel 50 watt fender style from a bassman head that was damaged in a fire. I reused the filter caps and all seemed fine until the amp sat unused for about a week. There is now a strange distortion that seems to decrease the longer the amp is played. I just wonder if the dousing the filter caps got from the fire hose has caused them to retain moisture. The caps are Sprague Atoms that were installed in the amp about a year before the fire. Anyone have any experience with "wet" electrolytics?
    Prolly more likely one of those carbon comp resistors but anything's possible. It needs a good drying out. If you live in a desert climate leave it outside for a few days. Otherwise stuff it in a trash bag with a whole load of silica gel and tape it up real well,

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    Thanks for the suggestions, Prairie Dawg. I should have added that no other parts were reused other than the filter caps, transformers and tube sockets. I made a new board and built with all new components. I guess I will order new caps and eliminate them from the equation. Also, the amp sat unused for several years before I obtained it.

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    Senior Member Howlin' Mad Mac's Avatar
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    It could also be that the caps came thu the fire fine but are just wearing out like normal.

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    Quote Originally Posted by jvm View Post
    I built a single channel 50 watt fender style from a bassman head that was damaged in a fire. I reused the filter caps and all seemed fine until the amp sat unused for about a week. There is now a strange distortion that seems to decrease the longer the amp is played.
    It is very likely that what you hear is the cross-modulation of the audio with much larger ripple in the DC power supply.

    I just wonder if the dousing the filter caps got from the fire hose has caused them to retain moisture.
    More likely the heat damaged the caps so they're leaking too much and going into internal thermal runaway.
    The caps are Sprague Atoms that were installed in the amp about a year before the fire. Anyone have any experience with "wet" electrolytics?
    Don't mess with it. Replace all the electros. Just do it. A sudden cap failure can take your power transformer if you're unlucky and things fall the wrong way.

    Look for heat damage to wire insulation and corrosion on tube sockets, switches and pots too.

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    Bent Member Chuck H's Avatar
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    Can't believe no one caught this. You say you only salvaged the filters and transformers... Well I might suspect the transformers also. Lots of heat and moisture sensitive stuff in a transformer. If the transformers have paper bobbins they may be moist. If a chemical was used it may be reacting with the metals and "salting" creating little conductive pathways. If the transformers have mylar insulation they could have been damaged by the heat. If any transformer got hot enough I could even imagine the wrap insulation being damaged.

    I hope replacing the filters fixes the problem for you. It probably will.

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