Need help with hum in Two-Stroke

[sthebluesman]

I finally got the Maggie cab and the amp sounds great but I still have extra hum that I know should not be there. I am going to start trouble shooting later. I will post the first 1/2 of my assembly video on YouTube today under “Two-Stroke Amp Project.” The first place I am going to check for the hum is the heater wire placement. I am going to start from the simplest possible solution. I will reroute them the see if extra clearance from the speaker jacks will cure the problem. I notice on all of my Fenders that they are up above the sockets and not hugging the chassis as they are in mine. The only thing that is different on mine than from the book that I can see are the ground placements. I tied all of the electrolytic negative leads together under the board and ran them to a common ground at the bolt on the PT. I may end up buying the brass grounding plate and grounding everything exactly as it is in the book.
If anyone can think of any other possible solutions, let me know. Thanks.

[sthebluesman]

I think I found an answer from a response to my video on YouTube. The Mojo760 PT does not have a center tap on the 6.3v heater supply so it is necessary to use 100 ohm 1/2 watt resistors on each filament wire to ground. I will let you know if this solves the problem. The Weber PT in the book has a center tap on the 6.3v that goes to ground and is also in the schematic.

[Robin]

Also, be sure to dress the twisted pair of the 6.3v heater circuit away from the rest of the leads going to the tubes. This can be done by running the heater wires on the other side of the tube sockets from the rest of the leads or by lifting the heater wires above the sockets and allowing them to float above the rest of the wiring. Please post the results of adding the artificial center tap.

[BenDr]

Hiya stblues.

Hey, maybe you could post before and after sound clips?

[sthebluesman]

Here is the YouTube video I posted yesterday with the hum. The amp still sounds great. I put the resistors on last night and that was the problem. I will post another video today.

[Author]

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