19-02-2020, 12:38 PM
This set has been giving me problems since my last post. One was that the audio would gradually fade out but not completely & the other was a rustling noise in the background on both wavebands throughout its tuning range. The fading problem was, I discovered, caused by...me! I'd put a 51K resistor in place of a 500K from pin2 to pin 6 of the FC4, most other radios that use the FC4 have around 50K, some 100K but mine originally had 500K!?! Still, that got rid of the fading issue. The rustling has been another matter altogether. I must confess that in my ignorance I put it down to sheer age, the set is after all, nearly 90 years old. I decided to do some research across several forums to see if others had experienced the same issue. Lo! It came to pass they had but seemed more prevalent in America. After much searching, going square eyed & reading far too much clap trap the answer would appear to have its roots in mica capacitors. I've always been led to believe they are amongst the most reliable but it would appear that time is catching up with them. They suffer from a number of issues, one of which is called silver migration. This can be a cause of the rustling, popping & f*rting noises. I also stumbled across a paper written in 1960(!) about their failure modes & causes. Link here: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjU9b7999vnAhWVEMAKHVTWDtQQFjAAegQIARAB&url=https%3A%2F%2Fescies.org%2Fdownload%2FwebDocumentFile%3Fid%3D62188&usg=AOvVaw04lQQ5ao10e6UqL2TWJLvf
It's a PDF & makes interesting reading. I replaced the capacitor in the Defiant, the only one I had left alone by the way , applied some power & once it had warmed through (takes about 30-45 seconds) it was like listening to a different set. Now, that particular fault could have gone unnoticed (and to some extent it did) for a very long time but it's a testament to the original design & build that it still functioned in an acceptable way. This set is probably one of my favourites & I have no idea why, it's nothing special to look at but does have a certain presence. Have a good day one & all.
It's a PDF & makes interesting reading. I replaced the capacitor in the Defiant, the only one I had left alone by the way , applied some power & once it had warmed through (takes about 30-45 seconds) it was like listening to a different set. Now, that particular fault could have gone unnoticed (and to some extent it did) for a very long time but it's a testament to the original design & build that it still functioned in an acceptable way. This set is probably one of my favourites & I have no idea why, it's nothing special to look at but does have a certain presence. Have a good day one & all.
