Hello, I saved a really nice Harmon Kardon 330A as it was being carried to the dumpster, it was a really lucky coincidence that I ran into it when I did. Anyways, When I got home and hooked it up to my system, I immediately noticed that the left channel was extremely quiet in comparison to the right channel. The only remedy is to turn the balance knob almost 95% to the left to get them to roughly balance. I plugged headphones into the amplifier and the left channel is still quiet. I removed the jumpers from the back of the HK330A and plugged in a preamp from another amplifier and it sounded good. I then wired the preamp of the HK330A and plugged it into the other amplifier, and the channel imbalance is present. This leads me to believe that the preamp is the source of the problem. I tried using deoxit on the switches and pots, making sure to thoroughly clean them all. The problem was still present. I then replaced a capacitor on the preamp board that seems to have had leaked at some point in the past. There was a brown stain on the board where the capacitor was, so I replaced that capacitor. But the problem was still present. I see two large capacitors on the pre-driver board that seem to have leaked at some point in the past, but as aforementioned, I believe that the problem lies in the preamp section. Should I go ahead and replace the large caps in the pre-driver section anyway? What else should I check/do? I am relatively new to this level of circuitry and only have a basic understanding of vacuum tube amplifiers. Thank you!