UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - My first valve radio project

TonyDuell · 27th Dec 2016, 10:17 pm

To me this sounds like the HT secondary winding is fine. It's not open-circuit (that's what the first test shows). Most of the time the 'centre tap' is actually a junction between the 2 halves of the winding, made at the transformer solder tag, so there's no wire in the transformer that could break to disconnect the tap and leave the entire winding continuous.

But it would appear that there is no connection between the centre tap and the chasiss through the bias network. This would explain why you see no output from the rectifier. In fact the rectifier could be fine, C26 (Trader Sheet) could be charging, but because there is no circuit from the centre tap back to the chassis, a meter check between rectifier cathode and chassis will show no voltage.

Anyway, I would check R19 and R20 (Trader Sheet) next.

27th Dec 2016, 10:17 pm	#134
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: My first valve radio project - Philips 462A To me this sounds like the HT secondary winding is fine. It's not open-circuit (that's what the first test shows). Most of the time the 'centre tap' is actually a junction between the 2 halves of the winding, made at the transformer solder tag, so there's no wire in the transformer that could break to disconnect the tap and leave the entire winding continuous. But it would appear that there is no connection between the centre tap and the chasiss through the bias network. This would explain why you see no output from the rectifier. In fact the rectifier could be fine, C26 (Trader Sheet) could be charging, but because there is no circuit from the centre tap back to the chassis, a meter check between rectifier cathode and chassis will show no voltage. Anyway, I would check R19 and R20 (Trader Sheet) next.