I have a blackface bassman AA864 that I may be having trouble with. I haven't played through a blackface bassman in many years and I wanted to make sure what I am hearing through the bass channel in correct. Two questions actually...
1. The normal channel is perfect. The bass channel sounds muffled which i'm assuming is because of the filtering for bass. The weird thing is that even though the volume and bass controls work fine, the treble seems to control volume as well. If the treble is on 0, then I can crank the volume and there is hardly any volume. If the treble is on 10, then the volume control turns up as it should. Loud. Is this the way that this channel works in these amps? Is it because the treble control is set up for a bass instrument ans filters out most of a guitar signal as it is turned down? Is it normally muffled like this?
2. Hum issue... The normal channel gets no hum whatsoever when the bass channels tubes are pulled. Sounds great. When the 2 bass channel preamp tubes are put back in, the amp hums. Not crazy loud but enough to be annoying. This hum occurs as soon as the amp is taken off of standby. It hums with no guitar plugged in. Volume controls do not change the hum. The filter caps we're replaced not too long ago. I tried about 6 fairly new 12ax7's in the normal channel and they all sound good with no hum. When I try them in the bass channel, the amp hums with all of them. So it's probably not the tubes. The cathode 25uF caps have been replaced. The other caps in that channel are original (the blue ones). The grounding scheme is original as well as the tube sockets (they are in good shape). The only thing replace in this amp is the filter caps and cathode 25uF caps and the pots. Brand new 6L6's too. Any ideas on what this could be?
Thanks.
1. The normal channel is perfect. The bass channel sounds muffled which i'm assuming is because of the filtering for bass. The weird thing is that even though the volume and bass controls work fine, the treble seems to control volume as well. If the treble is on 0, then I can crank the volume and there is hardly any volume. If the treble is on 10, then the volume control turns up as it should. Loud. Is this the way that this channel works in these amps? Is it because the treble control is set up for a bass instrument ans filters out most of a guitar signal as it is turned down? Is it normally muffled like this?
2. Hum issue... The normal channel gets no hum whatsoever when the bass channels tubes are pulled. Sounds great. When the 2 bass channel preamp tubes are put back in, the amp hums. Not crazy loud but enough to be annoying. This hum occurs as soon as the amp is taken off of standby. It hums with no guitar plugged in. Volume controls do not change the hum. The filter caps we're replaced not too long ago. I tried about 6 fairly new 12ax7's in the normal channel and they all sound good with no hum. When I try them in the bass channel, the amp hums with all of them. So it's probably not the tubes. The cathode 25uF caps have been replaced. The other caps in that channel are original (the blue ones). The grounding scheme is original as well as the tube sockets (they are in good shape). The only thing replace in this amp is the filter caps and cathode 25uF caps and the pots. Brand new 6L6's too. Any ideas on what this could be?
Thanks.
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