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

PJL · 27th Jan 2023, 12:10 am

Sort the missing field coils out first. The service data is a bit confusing and it would be good if someone who owns one of these can confirm that the console has a single speaker and the field coil is 400 ohms. The total voltage drop on the field coil is given as 80V in the service data which gives us 200mA and 16W dissipation.

Ideally you should find a choke with a similar series resistance and current capability but a 200mA choke will be a much lower resistance so you would still need a series resistance. I would therefore go for a suitably rated 400ohm resistor but you will need to find a suitable place to mount it as it is going to get HOT.

A request for a 12" 4ohm speaker here might bring up something.

27th Jan 2023, 12:10 am	#48
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: What did I get myself into? Murphy A40C. Sort the missing field coils out first. The service data is a bit confusing and it would be good if someone who owns one of these can confirm that the console has a single speaker and the field coil is 400 ohms. The total voltage drop on the field coil is given as 80V in the service data which gives us 200mA and 16W dissipation. Ideally you should find a choke with a similar series resistance and current capability but a 200mA choke will be a much lower resistance so you would still need a series resistance. I would therefore go for a suitably rated 400ohm resistor but you will need to find a suitable place to mount it as it is going to get HOT. A request for a 12" 4ohm speaker here might bring up something. Last edited by PJL; 27th Jan 2023 at 12:15 am.