Tube Preamp L&R Channel different current draw
 

Hi,
I need to determine why the left channel of my phono tube pre-amp is drawing 15 ma while the right channel is drawing 10 ma. I assume the left channel is at fault since there is also some hum on the left channel. I assume the problem is either a tube or a bad electrolytic capacitor. I guess I could swap L and R tubes to determine if the problem follows the tubes but not so easy on my pre-amp. Any suggestions on what I should look for and how to test capacitor in circuit would be greatly appreciated. The pre-amp has separated B+ supply which are at the same voltage.
Thanks.