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Hey All,
Just for kicks I decided to put my Bassman back to stock a little bit, to try some of the Fender mods that were taken out earlier. I was happy with it as-is, so I didn't go TOO much into perfectly doing it, but I wasn't sloppy about it. Here's what I found:
1. There are two schematics of this amp floating around. One has a 1000pF and a 500pF cap on the plate load resistors of the first stage of each channel. The other does not show these caps. Just be aware.
2. I reinstalled the 220k feedback resistors on the 6L6 plates, since they had been removed from my amp. The original terminal strip was still there, with those 2 oF caps soldered to it but not attached to the circuit. I followed the Fender layout, using regular wire, and the amp hummed. Whether 60 or 120Hz, I don't know (no scope). So I tried it with shielded wire - about half the hum, but still enough to be noticeable. Controls had no effect on the hum. So I yanked them. I figure this MAY explain why it was such a short-lived "improvement..."
3. I <DID> lower the values of the tone stack in the Bass channel, to a .022 & .047. It seems to have taken out some of the super-low freqs, but I'll know more about that when I can crank it up. It's not as woolly as before, and more guitar-friendly. But I always use the Normal channel for bass, anyway!
Like I said, I didn't go into too much depth trying to perfect it all, or to figure out where the hum was coming from. All I know is, I disconnected the wires and the hum was gone.
Justin
Just for kicks I decided to put my Bassman back to stock a little bit, to try some of the Fender mods that were taken out earlier. I was happy with it as-is, so I didn't go TOO much into perfectly doing it, but I wasn't sloppy about it. Here's what I found:
1. There are two schematics of this amp floating around. One has a 1000pF and a 500pF cap on the plate load resistors of the first stage of each channel. The other does not show these caps. Just be aware.
2. I reinstalled the 220k feedback resistors on the 6L6 plates, since they had been removed from my amp. The original terminal strip was still there, with those 2 oF caps soldered to it but not attached to the circuit. I followed the Fender layout, using regular wire, and the amp hummed. Whether 60 or 120Hz, I don't know (no scope). So I tried it with shielded wire - about half the hum, but still enough to be noticeable. Controls had no effect on the hum. So I yanked them. I figure this MAY explain why it was such a short-lived "improvement..."
3. I <DID> lower the values of the tone stack in the Bass channel, to a .022 & .047. It seems to have taken out some of the super-low freqs, but I'll know more about that when I can crank it up. It's not as woolly as before, and more guitar-friendly. But I always use the Normal channel for bass, anyway!
Like I said, I didn't go into too much depth trying to perfect it all, or to figure out where the hum was coming from. All I know is, I disconnected the wires and the hum was gone.
Justin