[Harp-L] Re: Identifying hazardous amps



Isn't the reason the amplifiers tube filaments are wired in series not that the amp lacks an isolation transformer but that the amp doesn't have a filament transformer? I've seen plenty of old radios with isolation transformers but no filament transformer. Why can't you ground the chasis of an amp lacking an isolation transformer? Power tools don't have isolation transformers and they're grounded. Isn't the purpose of an isolation transformer to isolate the amplifier from electrical noise? I don't have a Harmony 400 schematic in front of me but it seems likely that simply plugging one into a gfci protected circuit would solve the problem. Unlike the situations with many early amplifiers where the chassis is connected to the incoming line voltage via a capacitor or pair of capacitors where a gfci won't work because the voltage and current involved ends up below the trip threshold of the gfci a straight short to ground would quickly trip the gfci. Personally I'd rather be depending on a gfci than a ground and ultimately a panel breaker set to trip at 15 amps. If there's a good reason besides noise that you can't ground an unisolated circuit I'd really like to have it explained to me. Thanks, fjm




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