Miniature 'Convette' transformer turns ratio? - UK Vintage Radio Repair and Restoration Discussion Forum

thevalveset · 25th Jul 2017, 4:15 pm

Has anyone rewound the miniature mains transformer in an Amplion 'Convette' model P.R.I. Designed to replace the combined HT and LT battery type B114.

The 'Convette' is designed to supply 1.5V LT and 70V (69V) HT.
I found the HT winding O/C and have just pulled off the HT winding having carefully un-threaded the continuous iron tape laminations.
Incredibly there were 2939 turns of 44s.w.g. wire on this HT winding, giving a 'turns per volt' figure of around 42!
I am amazed, having been used to rewinding transformers with t.p.v's of anywhere between 3 t.p.v. and 1 t.p.v.
It has to be correct as I counted every turn off the bobbin to find the break right at the start!
Comments please.
Ta,
Dave

TrevorG3VLF · 25th Jul 2017, 7:17 pm

ludens transformers gives design details. 42t/v would seem to be necessary with a very small core. I have a very dubious memory that a one inch square core will need up to 8t/V depending on the iron.
I do not know what continuous iron tape laminations is. A toroidal transformer will have a single continuous tape lamination. Please post a picture.
Some small transformers are designed to stand a short circuit, perhaps this is one of them.

Herald1360 · 25th Jul 2017, 11:30 pm

Continuous tape sounds a bit like what C-cores would be if they weren't sawn in half to make Cs after winding the tape into a thick walled oval cylinder.

Is the TX one where the tape core is effectively wound round one side of the winding on the bobbin?

25th Jul 2017, 4:15 pm	#1
thevalveset Tetrode Join Date: Oct 2007 Location: Nottingham, Nottinghamshire, UK. Posts: 73	Miniature 'Convette' transformer turns ratio? Has anyone rewound the miniature mains transformer in an Amplion 'Convette' model P.R.I. Designed to replace the combined HT and LT battery type B114. The 'Convette' is designed to supply 1.5V LT and 70V (69V) HT. I found the HT winding O/C and have just pulled off the HT winding having carefully un-threaded the continuous iron tape laminations. Incredibly there were 2939 turns of 44s.w.g. wire on this HT winding, giving a 'turns per volt' figure of around 42! I am amazed, having been used to rewinding transformers with t.p.v's of anywhere between 3 t.p.v. and 1 t.p.v. It has to be correct as I counted every turn off the bobbin to find the break right at the start! Comments please. Ta, Dave

25th Jul 2017, 7:17 pm	#2
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Miniature 'convette' transformer turns ratio? ludens transformers gives design details. 42t/v would seem to be necessary with a very small core. I have a very dubious memory that a one inch square core will need up to 8t/V depending on the iron. I do not know what continuous iron tape laminations is. A toroidal transformer will have a single continuous tape lamination. Please post a picture. Some small transformers are designed to stand a short circuit, perhaps this is one of them.

25th Jul 2017, 11:30 pm	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Miniature 'Convette' transformer turns ratio? Continuous tape sounds a bit like what C-cores would be if they weren't sawn in half to make Cs after winding the tape into a thick walled oval cylinder. Is the TX one where the tape core is effectively wound round one side of the winding on the bobbin? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O