Aurora again - UK Vintage Radio Repair and Restoration Discussion Forum

Boom · 16th Apr 2011, 6:47 pm

On the Aurora quckstart guide in note 2) it states that if used with an ac/dc set that an isolation transformer should be used between the Aurora and the tv. (as distinct from a mains isolation transformer.)

Can I buy such a device or are there any clever clogs here who can suggest number of turns, type of former etc to built one?

Thanks

mark pirate · 16th Apr 2011, 6:51 pm

I asked the same question, here is the link to the thread.
https://www.vintage-radio.net/forum/...ad.php?t=62908

Mark

Boom · 16th Apr 2011, 7:23 pm

Thanks Mark but that thread seems to rely on caps for the isolation. I was interested in using two coils on a common former inside a plastic box to give total and complete isolation. So far the losses have been too severe probably because I have got the turns wrong.

ppppenguin · 16th Apr 2011, 8:13 pm

You don't need an isolating transformer between the Aurora and the TV. The reasoning behind all this is that if the TV chassis is live and the aerial isolator fails then the Aurora and any video kit connected to it will go live. It may well badly damage the Aurora and other kit to have fault currents flowing.

To avoid this nasty situation it's a good idea to use an external isolator in the aerial feed. This could be a transformer (a ferrite ring with a few turns for each of primary and secondary should work) or a couple of class Y caps in a plastic box. One each for centre and braid.

I'm a naughty boy and don't bother but I do make very sure my TV chassis are connected to neutral and I use an RCD.

Boom · 16th Apr 2011, 8:17 pm

Thanks Jeffrey that is basically what I am asking but I don't want to rely on capacitors for isolation. How many turns to use now.

BTW I've just had a look at the TV22 diagram and it seems that the input coil is already isolated by two windings. It would do the same job to just remove the cap that ties it to deck.

ppppenguin · 16th Apr 2011, 8:30 pm

Class Y caps are fine. Honestly. THat's what they are made for.

As for number of turns on a ferrite ring I'd start with 8 or so and see how much it mucks up the signal. On channel 1 you might need a few more, at the top of band 3 it may be too many. I'm sure it can be calculated but I'd suck it and see. Use a small ring, no more than 25mm across, preferably smaller. This is VHF you're doing, not audio.

evingar · 16th Apr 2011, 9:31 pm

Quote:

Originally Posted by Boom

Thanks Jeffrey that is basically what I am asking but I don't want to rely on capacitors for isolation. How many turns to use now.

I used an off-the-shelf 1:1 transformer for mine - It was a type designed to isolate serial digital video (SDI). Not ideal, but works OK and is a neat solution constructionally.

16th Apr 2011, 6:47 pm	#1
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Aurora again On the Aurora quckstart guide in note 2) it states that if used with an ac/dc set that an isolation transformer should be used between the Aurora and the tv. (as distinct from a mains isolation transformer.) Can I buy such a device or are there any clever clogs here who can suggest number of turns, type of former etc to built one? Thanks

16th Apr 2011, 6:51 pm	#2
mark pirate Dekatron Join Date: Mar 2008 Location: Worthing, West Sussex, UK Posts: 5,185	Re: Aurora again I asked the same question, here is the link to the thread. https://www.vintage-radio.net/forum/...ad.php?t=62908 Mark

16th Apr 2011, 7:23 pm	#3
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: Aurora again Thanks Mark but that thread seems to rely on caps for the isolation. I was interested in using two coils on a common former inside a plastic box to give total and complete isolation. So far the losses have been too severe probably because I have got the turns wrong.

16th Apr 2011, 8:13 pm	#4
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Aurora again You don't need an isolating transformer between the Aurora and the TV. The reasoning behind all this is that if the TV chassis is live and the aerial isolator fails then the Aurora and any video kit connected to it will go live. It may well badly damage the Aurora and other kit to have fault currents flowing. To avoid this nasty situation it's a good idea to use an external isolator in the aerial feed. This could be a transformer (a ferrite ring with a few turns for each of primary and secondary should work) or a couple of class Y caps in a plastic box. One each for centre and braid. I'm a naughty boy and don't bother but I do make very sure my TV chassis are connected to neutral and I use an RCD.

16th Apr 2011, 8:17 pm	#5
Boom Retired Dormant Member Join Date: Jan 2007 Location: Westbury, Wiltshire, UK. Posts: 2,451	Re: Aurora again Thanks Jeffrey that is basically what I am asking but I don't want to rely on capacitors for isolation. How many turns to use now. BTW I've just had a look at the TV22 diagram and it seems that the input coil is already isolated by two windings. It would do the same job to just remove the cap that ties it to deck.

16th Apr 2011, 8:30 pm	#6
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Aurora again Class Y caps are fine. Honestly. THat's what they are made for. As for number of turns on a ferrite ring I'd start with 8 or so and see how much it mucks up the signal. On channel 1 you might need a few more, at the top of band 3 it may be too many. I'm sure it can be calculated but I'd suck it and see. Use a small ring, no more than 25mm across, preferably smaller. This is VHF you're doing, not audio.