Wax condensers


Allan Isaacs
 

After the RA!7 discussion a couple of old domestic radios arrived here for repair.
I chose the Columbia C301, reported as having been in the customer's garage for donkeys years, and which looked untouched since it was last used probably in the 1970s.
I decided to just replace all eight of its wax-covered condensers and measure them as a matter of interest.
The results were not unexpected.
http://www.radiomuseum.co.uk/C301.html
Oddly the two condensers that had risen in value the most were in the audio circuit with the worst more than 17 times its marked value and that being the one usually responsible for ruining the output valve.
Usually I find the more the change in value the worse the leakage.
But why is it that this particular condenser is so bad?
I notice C22 (0.01uF) is not a wax variety but a tiny plastic type. I'll swap that next. Maybe the designers thought it would be better in some way for tone control.. but why?
I guess an RA17 of simiar vintage would be not much different?
Allan G3PIY

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