Very faint hum
- Thread starter Jimb0
- Start date
Can you double check the output of the 6.3V DC supply on the power supply board?
If that looks good, clip lead the center lug of each 6C45P socket to the ground buss wire and recheck to see if the noise is still there.
If that looks good, clip lead the center lug of each 6C45P socket to the ground buss wire and recheck to see if the noise is still there.
Remove those clip leads and clip them between terminals 5 and 10 on each output transformer (where the teflon wires connect).
If the original test reduced the level of hum, that is indicative of noise being picked up in the wiring going from the RCA jacks to the selector, attenuators, and tube sockets. If the noise is not dependent on the position of the attenuator (which you indicated before), then I would be suspicious of layout issues.
The Mainline is exceptionally sensitive to layout, and any deviations present the possibility of problems, so this may be a rather difficult issue to track down.
If the original test reduced the level of hum, that is indicative of noise being picked up in the wiring going from the RCA jacks to the selector, attenuators, and tube sockets. If the noise is not dependent on the position of the attenuator (which you indicated before), then I would be suspicious of layout issues.
The Mainline is exceptionally sensitive to layout, and any deviations present the possibility of problems, so this may be a rather difficult issue to track down.
Clip leads are wires with alligator clips on the ends. I'm not suggesting that you cut the wires...
Yes, those are in the correct spot for the first test.
For the second test, move each clip lead to connect terminal 5 and terminal 10 on each output transformer together.
For the second test, move each clip lead to connect terminal 5 and terminal 10 on each output transformer together.
That didn't actually fix anything, it's just another test.
The next test is to disconnect the end of the 10uF cap that goes to the red wire leading to each output transformer, then check for noise again.
The next test is to disconnect the end of the 10uF cap that goes to the red wire leading to each output transformer, then check for noise again.
The clip leads should be out for that next test.
Now you'll want to move the amp to see if that changes.
This, to me at the moment at least, indicates the output transformers are picking up some noise from somewhere.
This, to me at the moment at least, indicates the output transformers are picking up some noise from somewhere.
