guitar amp hum

excellrec · 8th October 2004

i've got a 67' fender bassman head that hums pretty bad.. with nothing plugged into it. Any guesses as to what this might be? I've got a newer fender that will plug into the same outlet and be pretty much silent. This bassman head has had the three prong installed. it's had sprague orange drop caps replacing all the filter caps, and it has newish mesa tubes in it right now, any obvious easy things i should look to first?

I also have another question regarding the newer fender amp, it is an m-80 kind lower end deal of about ten years age. Not to long ago I noticed something odd about it.... well A. i noticed that the eq'ed sucked reallllllly bad, i mean reallllll bad, when you twist a knob it sounds like you just plugged into a phaser, and B. when you turn all three knobs (low,mid,high) to 0, nothing comes through at all... and it happens in a very non-linear fashion, signal will be coming through, then all the sudden you go down past 1 and it cuts by like 30db (a little something still barely eeks through) i presume this isnt normal, i never noticed it before, but i've only had this amp a month or two.
so, any ideas?? I'll probly have to talk to a local tech, but i thought i'd run it by some forums first to see if i could do anything.

thanks guys/gals, Arit

tINY · 8th October 2004

Quote:

Originally posted by excellrec
i've got a 67' fender bassman head that hums pretty bad.. with nothing plugged into it. Any guesses as to what this might be? I've got a newer fender that will plug into the same outlet and be pretty much silent. This bassman head has had the three prong installed. it's had sprague orange drop caps replacing all the filter caps, and it has newish mesa tubes in it right now, any obvious easy things i should look to first?

I also have another question regarding the newer fender amp, it is an m-80 kind lower end deal of about ten years age. Not to long ago I noticed something odd about it.... well A. i noticed that the eq'ed sucked reallllllly bad, i mean reallllll bad, when you twist a knob it sounds like you just plugged into a phaser, and B. when you turn all three knobs (low,mid,high) to 0, nothing comes through at all... and it happens in a very non-linear fashion, signal will be coming through, then all the sudden you go down past 1 and it cuts by like 30db (a little something still barely eeks through) i presume this isnt normal, i never noticed it before, but i've only had this amp a month or two.
so, any ideas?? I'll probly have to talk to a local tech, but i thought i'd run it by some forums first to see if i could do anything.

thanks guys/gals, Arit

Check the voltage rails on that bassman, you may have a Power Supply issue.

Not sure on the filter. But it sounds like you may have smoked a summing amp. Check for hot/burned op-amps.

-tINY

Marty Shields. · 13th October 2004

There could be several reasons for Hum,Check Valves the 6L6's are ok,and matched for emission,if too far out of balance they will cause hum.
Check that a resistor in the power supply hasn't gone high or open, check ps for correct voltages, and bias voltage hasn't gone low,
check caps on cathode resistors in preamp.
Test unit with a balanced load on the imput.
all this is hoping your filtercaps are ok.Hope this helps.

Marts.

8th October 2004	#1
excellrec Gear maniac Joined: Nov 2003 Location: minneapolis Posts: 236 Thread Starter	guitar amp hum i've got a 67' fender bassman head that hums pretty bad.. with nothing plugged into it. Any guesses as to what this might be? I've got a newer fender that will plug into the same outlet and be pretty much silent. This bassman head has had the three prong installed. it's had sprague orange drop caps replacing all the filter caps, and it has newish mesa tubes in it right now, any obvious easy things i should look to first? I also have another question regarding the newer fender amp, it is an m-80 kind lower end deal of about ten years age. Not to long ago I noticed something odd about it.... well A. i noticed that the eq'ed sucked reallllllly bad, i mean reallllll bad, when you twist a knob it sounds like you just plugged into a phaser, and B. when you turn all three knobs (low,mid,high) to 0, nothing comes through at all... and it happens in a very non-linear fashion, signal will be coming through, then all the sudden you go down past 1 and it cuts by like 30db (a little something still barely eeks through) i presume this isnt normal, i never noticed it before, but i've only had this amp a month or two. so, any ideas?? I'll probly have to talk to a local tech, but i thought i'd run it by some forums first to see if i could do anything. thanks guys/gals, Arit

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13th October 2004	#3
Marty Shields. Gear Head Joined: Jan 2004 Location: Tasmania, Aus't Posts: 66	There could be several reasons for Hum,Check Valves the 6L6's are ok,and matched for emission,if too far out of balance they will cause hum. Check that a resistor in the power supply hasn't gone high or open, check ps for correct voltages, and bias voltage hasn't gone low, check caps on cathode resistors in preamp. Test unit with a balanced load on the imput. all this is hoping your filtercaps are ok.Hope this helps. Marts.