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|8/8/2005 2:13 AM|
|Greg Simon||Re: 60 cycle hum problems in Silvertone 1484, Please Hel|
Well today I finally got a chance to mess with the amp some more. I disconnected the 500pf, and then the .003uf also, and no difference at all in the hum level. I also switched around the bias feed wires to the plates of the power tubes which someone else had suggested. It didn't make much sense to me, but it didn't work to get rid of the hum either. It actually made the amp get a high freq parasitic, so I switched them back again. I also disconnected channel 1 where it mixes into the reverb at the 500pf junction, and that didn't make a difference either.
The tone stack for channel 2, where all the noise is, is right behind the power transformer. I'm using shielded cable going from and to the components in the amp chassis, but some components are mounted between the pots and some terminals right behind the power transformer. If I stick a piece of steel in between the two, it doesn't make much difference or gets worse depending on where I move the steel. I was thinking though that maybe this could be where it is picking up the hum? Maybe it is getting on a grid wire and being amplified and that is why it appears at the plate of stage 2, channel two? The components were mounted here on the stock setup also, but it doesn't hum this bad stock. The stock setup also used ceramic caps, but I used film caps. I didn't increase the gain all THAT much but was thinking I could back the gain down of channel 2 to reduce the hum. Channel 1 has WAY more gain with the EF86, but it doesn't hum at all.
|Greg Simon Just an update for those who are fo... -- 8/14/2005 7:53 PM|