BeatleFred
Super Member
Alrighty, well I got hold of a 7mm size nutdriver and I measured my BA-5K's bias setting on both channels. The spec in the Service Manual calls for connecting the amp to 8 ohm speakers, so I used my computer spkrs which are JBL HLS-410's. S.M. calls for a measured output of 180mA +- 1mA. I started with the left channel and I obtained an initial measurement of 294mA. After about 10 minutes, it settled down at 275mA and I turned the pot down (ever so carefully) to 180mA.
However, when I then measured the right channel, the meter read 8.86mA and it was steady at that value. I thought that in comparison to the Left channel's 295mA, 8.86 seemed a bit odd. Well, when I attempted to adjust the other pot, I noticed the reading did not change at all from 8.86, other than by perhaps a mere tenth of a millivolt. I kept turning the pot, both clockwise & counterclockwise, hoping to get it to rise so I could adjust it to 180mA, but nothing was happening except that 8.86mA.
EW- does it look like this pot is bad? If so, does this mean the measured value is really 8.86mA? I was hoping to listen to the BA-5K tonight ( BTW, this is the one I just bought the other week in Long Island , the pristine condition one w/ the factory data sheet). But I dunno if its such a good idea to use it with such a disparity in the measured values between the two channels. It does seem though, that the amp is a little cooler now than before, having atleast adjusted the left channel. Though, wouldnt the right side of the amp still be as hot as before, since the bias wasnt adjusted, but then again, why was the right side hot to begin with if the value was very low (8.86mA)? I suppose it could only be that the pot is bad and the actual right channel bias is alot higher than 180mA. I wish I knew what the actual reading was, but if that pot is bad, I guess there is no way I can tell. Maybe I can just estimate for now and leave the pot set at the 1/2 point of its full rotation ??
Well, perhaps I will warm up my 2nd of the 3 Monsters, also in near pristine condition, and see what I come up with when I try the bias measurements on that unit.
B/F
However, when I then measured the right channel, the meter read 8.86mA and it was steady at that value. I thought that in comparison to the Left channel's 295mA, 8.86 seemed a bit odd. Well, when I attempted to adjust the other pot, I noticed the reading did not change at all from 8.86, other than by perhaps a mere tenth of a millivolt. I kept turning the pot, both clockwise & counterclockwise, hoping to get it to rise so I could adjust it to 180mA, but nothing was happening except that 8.86mA.
EW- does it look like this pot is bad? If so, does this mean the measured value is really 8.86mA? I was hoping to listen to the BA-5K tonight ( BTW, this is the one I just bought the other week in Long Island , the pristine condition one w/ the factory data sheet). But I dunno if its such a good idea to use it with such a disparity in the measured values between the two channels. It does seem though, that the amp is a little cooler now than before, having atleast adjusted the left channel. Though, wouldnt the right side of the amp still be as hot as before, since the bias wasnt adjusted, but then again, why was the right side hot to begin with if the value was very low (8.86mA)? I suppose it could only be that the pot is bad and the actual right channel bias is alot higher than 180mA. I wish I knew what the actual reading was, but if that pot is bad, I guess there is no way I can tell. Maybe I can just estimate for now and leave the pot set at the 1/2 point of its full rotation ??
Well, perhaps I will warm up my 2nd of the 3 Monsters, also in near pristine condition, and see what I come up with when I try the bias measurements on that unit.
B/F