Fender Pro Junior HUM

[61dog]

Hey guys, I swapped the 1st preamp tube from 12AX7 to 5751 to tame the gain and mellow the tone a bit. Seems to have done the trick but the dreaded HUM is back. Should I just put the 12AX7 back, or is there something else I can do to keep the benefits of the 5751 and eliminate the HUM.



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[Herbie]

Hey guys, I swapped the 1st preamp tube from 12AX7 to 5751 to tame the gain and mellow the tone a bit. Seems to have done the trick but the dreaded HUM is back. Should I just put the 12AX7 back, or is there something else I can do to keep the benefits of the 5751 and eliminate the HUM.



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Good idea!

Is there HUM with the pedalboard connected or without any cable connected to input?

[Little Jay]

Are you sure it's not the P90s? Does it hum with humbuckers as well or does the hum change if you change position or move around the room?

[61dog]

definitely coming from the amp

[Herbie]

definitely coming from the amp

Does the turning of the volume pot change the hum?

Did it hum with the 12AX7?

Does the amp hum in other rooms and other outlets?

Are Your wall outlets grounded?

[lammie200]

Sorry to say but Pro Juniors tend to be noisy. You can try a lower gain tube in the other pre amp socket but I doubt that you will ever get the thing to be dead quiet though. Messing with the output transformer and circuit board can be a rabbit hole. One easy thing you can do, however, is remove the top screw on the back that secures the chassis to the cabinet. That can contact something inside that messes up the signal path. Good luck. Nice amps but meant to be played loud.

[pingu]

i’d try a few different tubes and try to
find a good noiseless one ....

ps
Ive never understood the lower-gain V1
tube swapping practice ....

whats the the difference between swapping in a lower gain tube and
just turning down a bit ....

i dont see see how swapping would get you any more clean headroom ....
surely to to get more clean headroom
one would need a higher wattage power section and suitable speaker

[61dog]

Yes, turning down reduce hum.
this little amp hums everywhere I try it