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Here's the schematic

Hi SOR,

It looks like you have blown the input FET. There is a weird feedback op-amp that is some sort of filter. My guess is that the blown input FET has a really high gate leakage current that makes it OK with a 100 ohm load, but that raising it to 49.9k (as shown in the schematic) causes everything to go haywire. It's not a tube problem and I wouldn't let anybody touch it other than Audio Research as they keep the identity of all of their transistors secret.

Hope this helps,
Charles Hansen

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