I'm restoring my 720A (B era) - see the doc wurly page here: https://docwurly.com/700-series-consoles-keep-em-straight-720-720a-720b-726-b/
It's the solid state version with a 140B amp.
The main issue I'm having is hum in the speaker. Also when I first switch it on, there's a fuzzy sound that comes through the speaker, and intermittently there's some fuzzy sounds and pops that come through the speaker.
So far, I've replaced all of the polarized electrolytic caps, as well as some of the resistors. I tied in and soldered some of these components into the leads of the original components, and there's a slight burning small when the amp is switched on which I bet is caused by these tie ins.
I also removed the cable that runs to the phono input, which reduced some noise and increased the clarity of the amp. I also replaced the built in power cable with an IEC port and removed the "death cap" that runs from the 120V power source to the fuse.
I'm still planning to:
-solder the replacement resistors straight to the circuit board to try to get rid of the burning smell
-replace the can caps with electrolytics mounted inside the chassis (I have some ideas of where to put the replacements, but suggestions are appreciated)
-replace more caps and resistors (I have ordered this kit from Tropical Fish Vintage and haven't installed all of the components yet: https://www.tropicalfishvintage.com/keyboard-parts/wurlitzer-140b-amplifier-rebuild-components )
-I also want to get into the volume and tone knobs on the cheek block and apply contact cleaner. Does anyone know how to access these potentiometers?
Do you have any other suggestions for removing the hum from the amp? Am I on the right track?
I also will need to make adjustments to the action of the keyboard, but I want to take care of the electronics first. Some keys require more force to hit than others. There are also some keys that are not muting properly.
I can update with some photos later if that would be helpful to see what's going on in and around the amp.
Many thanks!
It's the solid state version with a 140B amp.
The main issue I'm having is hum in the speaker. Also when I first switch it on, there's a fuzzy sound that comes through the speaker, and intermittently there's some fuzzy sounds and pops that come through the speaker.
So far, I've replaced all of the polarized electrolytic caps, as well as some of the resistors. I tied in and soldered some of these components into the leads of the original components, and there's a slight burning small when the amp is switched on which I bet is caused by these tie ins.
I also removed the cable that runs to the phono input, which reduced some noise and increased the clarity of the amp. I also replaced the built in power cable with an IEC port and removed the "death cap" that runs from the 120V power source to the fuse.
I'm still planning to:
-solder the replacement resistors straight to the circuit board to try to get rid of the burning smell
-replace the can caps with electrolytics mounted inside the chassis (I have some ideas of where to put the replacements, but suggestions are appreciated)
-replace more caps and resistors (I have ordered this kit from Tropical Fish Vintage and haven't installed all of the components yet: https://www.tropicalfishvintage.com/keyboard-parts/wurlitzer-140b-amplifier-rebuild-components )
-I also want to get into the volume and tone knobs on the cheek block and apply contact cleaner. Does anyone know how to access these potentiometers?
Do you have any other suggestions for removing the hum from the amp? Am I on the right track?
I also will need to make adjustments to the action of the keyboard, but I want to take care of the electronics first. Some keys require more force to hit than others. There are also some keys that are not muting properly.
I can update with some photos later if that would be helpful to see what's going on in and around the amp.
Many thanks!
