UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Advice needed on choosing a power transformer

G8HQP Dave · 18th Oct 2016, 11:54 am

The mains here in the UK is supposed to be 230V, but in most places it is still 240V and could lawfully be as high as 253V. It could also be below 220V, so if you can do so safely it might be worth measuring your mains voltage. It will vary a bit from day to day and at various times of day, but it probably won't vary very much. It is useful to know whether your mains is typically a bit high or low or about right.

300mA (not 300ma) should be more than enough, but be aware that most transformers are AC rated for a resistive load and you can't draw that same current continuously as DC via a rectifier and capacitor arrangement. There is not much point in using a transformer which is far too large as it will cost more and take up lots of chassis space. Best to choose one which is just a bit too large.

18th Oct 2016, 11:54 am	#5
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Advice needed on choosing a power transformer The mains here in the UK is supposed to be 230V, but in most places it is still 240V and could lawfully be as high as 253V. It could also be below 220V, so if you can do so safely it might be worth measuring your mains voltage. It will vary a bit from day to day and at various times of day, but it probably won't vary very much. It is useful to know whether your mains is typically a bit high or low or about right. 300mA (not 300ma) should be more than enough, but be aware that most transformers are AC rated for a resistive load and you can't draw that same current continuously as DC via a rectifier and capacitor arrangement. There is not much point in using a transformer which is far too large as it will cost more and take up lots of chassis space. Best to choose one which is just a bit too large.