Bare Knuckle Pickups Forum

Forum Ringside => Tech => Topic started by: Dmoney on November 19, 2011, 07:25:32 AM

Title: transformer isolation
Post by: Dmoney on November 19, 2011, 07:25:32 AM

So I've been up all night on the nightshift and looking at various things. This is nightshift round 1 and im feeling it!
I was looking at a couple of projects and got to spying something requiring a transformer with a ~235Vac 6VA secondary.
So not much power but close to UK mains voltage. This was an American article, so the transformer was stepping up 110Vac to 235Vac...

I started looking for a transformer that would do UK mains to 240Vac... then I remember UK mains is 240Vac... I briefly thought about the possibility of directly rectifying UK mains... putting live and neutral directly onto a rectifier. I then realised this is a stupid and dangerous idea.

so now I'm wondering what product just converts current, or if i wanted to get close to 240Vac into a rectifier, should I be looking at 110Vac dual secondary PT's?

Title: Re: transformer isolation
Post by: Frank on November 19, 2011, 07:42:48 AM

I can't stress this enough

NEVER DIRECTLY RECTIFY MAINS VOLTAGE WITHOUT AN ISOLATING TRANSFORMER

Danbury do a handy range of valve amp transformers, I've used this one in the past for preamps

http://livinginthepast-audioweb.co.uk/xfrmrvt247.php

I think they've added a few more since I last ordered from them, have a check

Title: Re: transformer isolation
Post by: Dmoney on November 19, 2011, 09:04:50 AM

I knew it wasn't correct as soon as the idea. I'm silly but not that silly. Still... I've not slept in over 24 hours so thought process is taking me a bit longer.

Thats exactly what I was looking for. cheers

If I used it for what I'm thinking, I feel like I'd have to mount it inside a chassis for safety. I'm not sure it would fit into what i'm planning. Now I know what I'm looking for I might do some googling when I'm back in work tonight and see what else is out there. I'd be using it for a snazzy dual polarity supply.

Title: Re: transformer isolation
Post by: HTH AMPS on November 19, 2011, 10:23:23 AM

if you want 240v on the secondary, just use a 1:1 isolation transformer.

Title: Re: transformer isolation
Post by: Dmoney on November 19, 2011, 02:29:54 PM

I'm struggling to find anything that is just a neat solution. small and just a toroid or something. The closest thing I know about is what Frank posted. Most things are just too big. hmm

Title: Re: transformer isolation
Post by: jpfamps on November 19, 2011, 06:59:16 PM

Tube Town do a useful range of small (and large) toroidals, eg

http://www.tube-town.net/ttstore/product_info.php/info/p2192_Torodial-30VA.html

Title: Re: transformer isolation
Post by: ToneMonkey on November 20, 2011, 09:04:28 PM

I'm 99% sure that the UK mains voltage is now classed as 230V to be in line with Europe.

It used to be 240V +/- 10% but they changed the tolerance so it's 230V +10% -5% (or something close), so nothing has actually changed other than the numbers.