UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Ferguson 621U

julie_m · 5th Oct 2018, 1:09 am

If the crackling is unaffected by the volume control, check the UABC80. With luck, there will be a dry joint on one of its pins or a component connected thereto. I say "with luck" because there is a nastier plausible failure mode which I'm sure you agree with me in hoping it isn't .....

The wavechange switch in an AM/FM set switches the HT to the anodes of the UCC85 and the triode of the UCH81, and it is possible for HT to track where it is not wanted. This can cause all manner of strange behaviour, and the fault probably will sound different on FM and AM.

If you can get the room really, really dark (you will also have to fit a temporary resistor in place of the set's scale lamps), you might be able to see a faint glow when the set crackles.

5th Oct 2018, 1:09 am	#15
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Ferguson 621U - help needed If the crackling is unaffected by the volume control, check the UABC80. With luck, there will be a dry joint on one of its pins or a component connected thereto. I say "with luck" because there is a nastier plausible failure mode which I'm sure you agree with me in hoping it isn't ..... The wavechange switch in an AM/FM set switches the HT to the anodes of the UCC85 and the triode of the UCH81, and it is possible for HT to track where it is not wanted. This can cause all manner of strange behaviour, and the fault probably will sound different on FM and AM. If you can get the room really, really dark (you will also have to fit a temporary resistor in place of the set's scale lamps), you might be able to see a faint glow when the set crackles. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.