I have an Emerson 659B AM/FM radio that I Have been working on. I replaced all the caps, cleaned the unit inside and out, added a fuse and set up the on/off switch to actually switch the "hot" side of the new polarized line cord. I am getting "hum" in AM or FM modes from the speaker Radio does tune around and play just fine in both bands but that darn hum is present! Using a scope, a check of the B+ shows a nice triangle wave at 60hz, my hum.. I replaced the multi section filter cap with a new multi section cap I got from AES. It is a 47uf, 80uf 160v unit made by CE Manufacturing (AES part number 34953).
I am starting to suspect this unit is supposed to have the small amount of hum as that is the way it was designed. I am considering adding more filter caps to smooth things out, any suggestions?
Steve
:Hello All,
:
:I have an Emerson 659B AM/FM radio that I Have been working on. I replaced all the caps, cleaned the unit inside and out, added a fuse and set up the on/off switch to actually switch the "hot" side of the new polarized line cord. I am getting "hum" in AM or FM modes from the speaker Radio does tune around and play just fine in both bands but that darn hum is present! Using a scope, a check of the B+ shows a nice triangle wave at 60hz, my hum.. I replaced the multi section filter cap with a new multi section cap I got from AES. It is a 47uf, 80uf 160v unit made by CE Manufacturing (AES part number 34953).
:I am starting to suspect this unit is supposed to have the small amount of hum as that is the way it was designed. I am considering adding more filter caps to smooth things out, any suggestions?
Here is what I think is happening. You are now switching hot side of the AC line. AC line goes to switch which is part of the volume control. Some hum is picked up and amplified by the 1st audio amplifier. That was the reason ground side of a radio was originally switched. This kept AC away from volume control.
Since you have a scope might consider hum cancelling? Feed some ripple out of phase to cancel hum. Since hum gets into 1st AF amplifier grid a little hum fed into the plate circuit should cancel. This takes a lot of experimenting.
Norm
:OH One more note.. The new polarized power cord puts the neutral on the chassis NOT the hot lead. I have considered flopping it back just for testing.
:
:Steve
:
::Hello All,
::
::I have an Emerson 659B AM/FM radio that I Have been working on. I replaced all the caps, cleaned the unit inside and out, added a fuse and set up the on/off switch to actually switch the "hot" side of the new polarized line cord. I am getting "hum" in AM or FM modes from the speaker Radio does tune around and play just fine in both bands but that darn hum is present! Using a scope, a check of the B+ shows a nice triangle wave at 60hz, my hum.. I replaced the multi section filter cap with a new multi section cap I got from AES. It is a 47uf, 80uf 160v unit made by CE Manufacturing (AES part number 34953).
::I am starting to suspect this unit is supposed to have the small amount of hum as that is the way it was designed. I am considering adding more filter caps to smooth things out, any suggestions?
I removed the AC from the pot and the hum went away. On this model of radio, you cannot remove the back without first removing the power cord, they are one assembly. Rather than try and continue to play with finding the proper value to phase in hum, I opted to put the switch back the way it was. The radio is much more safe than it was before because of the fuse.
It seems the more I play with trying to "stuff" in phase hum the worse tuning gets as I disturb the components around the posts for the tuning cans.
Thanks Again Norm...
:Steve
:
: Here is what I think is happening. You are now switching hot side of the AC line. AC line goes to switch which is part of the volume control. Some hum is picked up and amplified by the 1st audio amplifier. That was the reason ground side of a radio was originally switched. This kept AC away from volume control.
:
: Since you have a scope might consider hum cancelling? Feed some ripple out of phase to cancel hum. Since hum gets into 1st AF amplifier grid a little hum fed into the plate circuit should cancel. This takes a lot of experimenting.
:
:Norm
:
::OH One more note.. The new polarized power cord puts the neutral on the chassis NOT the hot lead. I have considered flopping it back just for testing.
::
::Steve
::
:::Hello All,
:::
:::I have an Emerson 659B AM/FM radio that I Have been working on. I replaced all the caps, cleaned the unit inside and out, added a fuse and set up the on/off switch to actually switch the "hot" side of the new polarized line cord. I am getting "hum" in AM or FM modes from the speaker Radio does tune around and play just fine in both bands but that darn hum is present! Using a scope, a check of the B+ shows a nice triangle wave at 60hz, my hum.. I replaced the multi section filter cap with a new multi section cap I got from AES. It is a 47uf, 80uf 160v unit made by CE Manufacturing (AES part number 34953).
:::I am starting to suspect this unit is supposed to have the small amount of hum as that is the way it was designed. I am considering adding more filter caps to smooth things out, any suggestions?