Adapting a 220v radio for 240v. - UK Vintage Radio Repair and Restoration Discussion Forum

'LIVEWIRE?' · 24th Jul 2013, 1:35 pm

The mains here measures ca. 245v. I know that if a low voltage transformer-in this case one with a secondary of some 20 to 25v-is wired in series with the mains TX primary, this will drop the excess voltage, and needs only to be rated at about 3 to 5VA, depending upon the current drawn by the radio from the mains. What i don't know (although perhaps I should!) is what, if any, connections, do you make to the primary of the added transformer?

TrevorG3VLF · 24th Jul 2013, 2:12 pm

You need to make an auto transformer.
There are two ways of doing this. I show a diagram how to do this.

Iwould prefer the first since the transformer is run on a slightly lower voltage so should run cooler.

The phasing of the must be correct or you will get more than you bargained for.

ukcol · 24th Jul 2013, 4:21 pm

Quote:

Originally Posted by 'LIVEWIRE?'

what, if any, connections, do you make to the primary of the added transformer?

See diagram.

Colin M

'LIVEWIRE?' · 24th Jul 2013, 7:46 pm

Thanks, chaps.

cannissolis · 24th Jul 2013, 8:37 pm

Out of interest the two ways shown of connecting the autotransformer will give slightly different Vout ie the first one will give one or two volts less than the latter and only the 20 volt winding needs to be capable of the rated current of the device to be powered so AC wall warts are ideal and can be suitably modified to run all sorts of 220v equipment

24th Jul 2013, 1:35 pm	#1
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Adapting a 220v radio for 240v. The mains here measures ca. 245v. I know that if a low voltage transformer-in this case one with a secondary of some 20 to 25v-is wired in series with the mains TX primary, this will drop the excess voltage, and needs only to be rated at about 3 to 5VA, depending upon the current drawn by the radio from the mains. What i don't know (although perhaps I should!) is what, if any, connections, do you make to the primary of the added transformer?

24th Jul 2013, 2:12 pm	#2
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Adapting a 220v radio for 240v. You need to make an auto transformer. There are two ways of doing this. I show a diagram how to do this. Iwould prefer the first since the transformer is run on a slightly lower voltage so should run cooler. The phasing of the must be correct or you will get more than you bargained for. Attached Thumbnails

24th Jul 2013, 7:46 pm	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Adapting a 220v radio for 240v. Thanks, chaps.

24th Jul 2013, 8:37 pm	#5
cannissolis Retired Dormant Member Join Date: Feb 2011 Location: Suffolk, UK. Posts: 25	Re: Adapting a 220v radio for 240v. Out of interest the two ways shown of connecting the autotransformer will give slightly different Vout ie the first one will give one or two volts less than the latter and only the 20 volt winding needs to be capable of the rated current of the device to be powered so AC wall warts are ideal and can be suitably modified to run all sorts of 220v equipment