Can anyone out there with a Motorola SK52W or similar 3-channel console tell me if they have any discernable hum out of the center (woofer) channel? And by 'discernable ' I mean can be heard from 8 feet away. Not trying to diagnose at this point, but more wondering if it's possibly a design issue. Hum is independent of volume level. Thx in advance
Motorola center channel hum
- Thread starter jkanclark
- Start date
Register to hide this ad
Sounds like power supply hum, have you redone the filter caps yet?
The side speakers aren't designed to produce that low a frequency but the center channel is.
On one of mine I still had a little hum after a cap job, so I used a choke in the power supply in place of a power resistor. Knocked out the remaining hum.
The side speakers aren't designed to produce that low a frequency but the center channel is.
On one of mine I still had a little hum after a cap job, so I used a choke in the power supply in place of a power resistor. Knocked out the remaining hum.
cademan
Lunatic Member
Yup! should not have any hum. My 3 channel Motorola is quiet quiet quiet! Your power supply filter capacitor is suspect. It would be the silver can on top of the chassis. Most Motorola 3 channels I have seen have had the disc capacitors under the chassis so the can would be the only thing that needs to be replaced.
I've already replaced the filter caps, which is why I wondered if it was a design issue. Would you mind roughing out where you placed the choke, and the choke specs themselves? Would be most appreciative
Thx filter caps have been replaced. It's not a bad hum, but definitely not quiet quiet quiet! Lol
cademan
Lunatic Member
New caps can sometimes be bad. It's been known to happen. Still could be a bad capacitor or bad ground connection. Make sure the negatives of all the new capacitors have their negatives connected to or close to the original can capacitor's tab. Make sure they are making good contact either with the chassis or center tap or both.
It should not hum at all.
Got any pics of this thing?
It should not hum at all.
Got any pics of this thing?
Last edited:
Here's a pic of the power amp. I'm rather suspicious of the blistered cap I've circled. It runs between the phase inverter and one of the center channel 6BQ5s. I'll snip one of the leads and test it when I get a minute or two.
