- volume control slider too sensitive
- audio volume too loud
- strong hum on audio
- loss of presets and clock unless 2xAA cells are fitted in
The radio has plenty of room inside and all components are through-hole. At a first glance the probable cause of hum is evident: 15VAC and audio line to speaker run together to/from the main board.
I have to build a (circa) 455 kHz to 12 kHz downconverter.
The IF system chip is BA4237L; the AM IF filter is marked SFU450B (thus 10 kHz BW at 450 kHz). First decision to be taken: should I pick the IF before or after the filter?
If I pick it after the filter I need a L.O. at + or - 12 kHz, so 462 or 438 kHz: how to make a stable one? (I will use my xtalfind tool to see if any of my surplus XTALs fall close to those values)
If I pick it before the filter I can make a stable 455 kHz L.O. and retune the receiver L.O. so that the resulting difference is 12 kHz. Would the incoming signal be too wide?
Let experiments begin!