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re: still trying to track down a hum...

Posted by mr9iron on September 17, 2012 at 10:45:20:
Hey,

thanks for the reply, yes this is the same schematic I have. the grid resistors to ground measure perfect, they are "Dales" supplied by Jim of course, from his resistor kit.

I have not checked my grounds to chassis DC resistance, I will see what I get tonight, but I do have all the grounds (12 ga. copper) on one buss soldered to a bridge that is attached to the PS bracket... that bracket is screwed into the chassis with star washers. before I put those in, I scraped away any paint and made sure the screws and washers "bite" to metal. I tried last night going right to chassis, with the buss, but no change..

The RCA's themselves are sandwiched in between two phenolic plates and then those plates are screwed to the chassis. I took them out to be sure this was the case. I don' think there can be a way for those RCA's to be touching any metal.

There is one slight improvement I noticed last night, and that is, if I remove the RCA grounds from the chassis there is like a slight extra buzz that will go away, if I touch both RCA grounds to the chassis I get a tiny extra buzz, it's not much, maybe a 5% improvement with no RCA ground. This made me wonder if there is something being grounded to the chassis that is causing this loop.... something I am not seeing....

I will check the the DC resistance tonight on all the grounds and see what I get..

thanks for your reply....

Jeff