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Vintage threads from the first ten years
Crate amps: Inrush current limiting
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 9/25/2000 6:01 AM |
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Tracy |
Crate amps: Inrush current limiting Hi I replace alot of output transistors in crate amps I see these blue MOV's in there and I wonder if there part of the problem. I have two identical amps in the shop. Can't think of the model off hand. it uses tip142 and tip147 darlington pairs. Both amps look brand new and are dead as hell. |
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| 9/25/2000 3:32 PM |
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| MBSetzer |
If its an inrush current limiter in series with incoming power, they are negative temperature coefficient varistors, they look like disk capacitors or spike-protecting MOV's. They start at significant resistance when cold and simply limit current depending on the ohms, then after heating up to operating temperature some have very little if any significant resistance. Turning the power off then back on before the limiter has had time to cool off can fry a circuit if the design completely depends on these instead of just using them for extra reliability. If you find out that's the case, you could either add some additional fixed resistance in series, maybe some fraction of the limiter's cold value, or make it switchable, essentially adding a standby switch, then you could use a larger ohm value than the cold limiter for extra protection. hope this makes sense, Mike *They say every man need protection . . .* - - BDylan & The Band |
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| 9/25/2000 8:41 PM |
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| Tracy |
Re: Thanks Hi MB That sounds really good! There's aman who needs protection! Tracy |
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