RS "Choke" output transformer - data wanted. - UK Vintage Radio Repair and Restoration Discussion Forum

Leon Crampin · 17th Oct 2007, 6:05 pm

Does anyone have the data sheet for the above? The transformer has fixing centres of about 62mm and has 8 terminals, designated A - D and 1 - 4.

Thanks for any help.

Leon.

ronbryan · 17th Oct 2007, 6:50 pm

Leon

Mickjjo has posted data on obsolete RS transformers including the "Midget Choke" output transformer, taken from an RS data book. Is this the one? No pin connections though.

https://www.vintage-radio.net/forum/...8&d=1145649381

The drawing (style Q) is on another page here.

https://www.vintage-radio.net/forum/...7&d=1145649242

Ron

Leon Crampin · 17th Oct 2007, 8:13 pm

Thanks Ron. I had seen these - unfortunately mine is a "Choke" rather than a "Midget Choke".

Leon.

pmmunro · 17th Oct 2007, 9:20 pm

The April/July 1971 edition of the "Radiospares" catalogue has the following listing:

"Choke" Choke O/P Trans. £0.780 each

"Clamp" construction, vacuum varnish impregnated. Connections to solder lugs.

Primary: 2.4k ohms (UL84) to 4.5k ohms (EL84) rated 60mA d.c. Primary has two taps at 1.5% and 7.5% for hum smoothing circuits.

Secondary: To match 3 ohm, 7 ohm or 15 ohm speech coils, rated 5.6W.

Dimensions: W 49.5mm H. 40.6mm D. 31.8mm FC. 61.0mm Wt. 14 oz.

If you need any more information, I will try to find a corresponding Radiospares data book and see if that can add anything.

(I only keep this catalogue to worry new RS reps. by telling them its a long time since I had a visit).

PMM.

Leon Crampin · 17th Oct 2007, 9:35 pm

Thanks very much Peter, that's the one.

If you could unearth the data sheet, that would be really useful. There are so many tappings on this transformer that it's possible to achieve a given ratio (approximately, at least) in several ways. The problem is that only the correct selection of primary and secondary taps will achieve the correct working core flux density and avoid possible DC saturation. I suspect this transformer is quite useful - I have two of them.

Leon.

igranic · 17th Oct 2007, 10:45 pm

Leon,

I think this may be half of what you are looking for!

Click image for larger version

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Sadly, I don't have a copy of the reverse. Apologies for the poor quality.

Edward

Leon Crampin · 17th Oct 2007, 11:52 pm

Edward - Brilliant!

Thanks very much for this - it's obviously a very useful transformer. The lack of ratio data doesn't really matter as I've measured all these already. What you can't easily do with an "unknown" transformer is assess where on the core magnetising curve you are operating. With the maker's data I can now use it as designed.

Many thanks once again,

Leon.

17th Oct 2007, 6:05 pm	#1
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	RS "Choke" output transformer - data wanted. Does anyone have the data sheet for the above? The transformer has fixing centres of about 62mm and has 8 terminals, designated A - D and 1 - 4. Thanks for any help. Leon.

17th Oct 2007, 6:50 pm	#2
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: RS "Choke" output transformer - data wanted. Leon Mickjjo has posted data on obsolete RS transformers including the "Midget Choke" output transformer, taken from an RS data book. Is this the one? No pin connections though. https://www.vintage-radio.net/forum/...8&d=1145649381 The drawing (style Q) is on another page here. https://www.vintage-radio.net/forum/...7&d=1145649242 Ron Last edited by ronbryan; 17th Oct 2007 at 6:57 pm.

17th Oct 2007, 8:13 pm	#3
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	Re: RS "Choke" output transformer - data wanted. Thanks Ron. I had seen these - unfortunately mine is a "Choke" rather than a "Midget Choke". Leon.

17th Oct 2007, 9:20 pm	#4
pmmunro Octode Join Date: Jul 2004 Location: Dundee, UK. Posts: 1,813	Re: RS "Choke" output transformer - data wanted. The April/July 1971 edition of the "Radiospares" catalogue has the following listing: "Choke" Choke O/P Trans. £0.780 each "Clamp" construction, vacuum varnish impregnated. Connections to solder lugs. Primary: 2.4k ohms (UL84) to 4.5k ohms (EL84) rated 60mA d.c. Primary has two taps at 1.5% and 7.5% for hum smoothing circuits. Secondary: To match 3 ohm, 7 ohm or 15 ohm speech coils, rated 5.6W. Dimensions: W 49.5mm H. 40.6mm D. 31.8mm FC. 61.0mm Wt. 14 oz. If you need any more information, I will try to find a corresponding Radiospares data book and see if that can add anything. (I only keep this catalogue to worry new RS reps. by telling them its a long time since I had a visit). PMM.

17th Oct 2007, 9:35 pm	#5
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	Re: RS "Choke" output transformer - data wanted. Thanks very much Peter, that's the one. If you could unearth the data sheet, that would be really useful. There are so many tappings on this transformer that it's possible to achieve a given ratio (approximately, at least) in several ways. The problem is that only the correct selection of primary and secondary taps will achieve the correct working core flux density and avoid possible DC saturation. I suspect this transformer is quite useful - I have two of them. Leon.

17th Oct 2007, 10:45 pm	#6
igranic Rest in Peace Join Date: Jan 2005 Location: North Bedfordshire, UK. Posts: 395	Re: RS "Choke" output transformer - data wanted. Leon, I think this may be half of what you are looking for! Sadly, I don't have a copy of the reverse. Apologies for the poor quality. Edward

17th Oct 2007, 11:52 pm	#7
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	Re: RS "Choke" output transformer - data wanted. Edward - Brilliant! Thanks very much for this - it's obviously a very useful transformer. The lack of ratio data doesn't really matter as I've measured all these already. What you can't easily do with an "unknown" transformer is assess where on the core magnetising curve you are operating. With the maker's data I can now use it as designed. Many thanks once again, Leon.