IF Transformer Cans - UK Vintage Radio Repair and Restoration Discussion Forum

RetiredHal · 8th Mar 2008, 1:06 pm

Hi, can somebody tell me how I can identify which adjustment slug belongs to which side of the IF transformer. Cct diagrams show both sides of the transformer to have a slugged coil. Access to these adjustments are from the top of the can and from the bottom (chassis/component) side of the can. I notice that most cans have a paint spot/ colour on one of the four connections. Does that mean something?
Whilst I can identify the physical connections of the IF transformer and relate these to the cct diagram, I really have no way of identifying which coil slug bottom or top belongs to which side of the transformer as it is inside a sealed can. Hope the question makes sense?

Cheers John

jim_jobe · 8th Mar 2008, 1:26 pm

According to the Radio Constructor, January 1949,page 470 the coil next to the chassis, i.e. the bottom one, should be the primary,connected to the anode of the preceding valve. The outer wire of the primary goes to the said anode, and the inner to HT+. The upper,secondary coil, outer wire goes to the grid of the following valve and the inner to AVC or ground. (See also RC May 1953, p 462.)
Having said all that I'm sure there are exceptions to the rule, and we all know about Sod's Law!
Jim

Chris55000 · 8th Mar 2008, 1:40 pm

Hi!

Unless the set-maker has specifically identified 'em on his repair words, there's no way of finding out except by dismantling the transformer and I'm sure you'd rather not do that!

For alignment of a standard AM superhet it's not all that important which order you align the IF stages, but for FM and TV IF strips that need aligning to a specific order you really *do* need a full Maker's sheet rather than a Trader jobbie, which may have "howlers" in it, or a Newnes book page which might have only a circuit and nothing else!

If you're adjusting something like a dual AM/FM transformer and have no data, use a trimming-tool with a clear mark on it, and mark a dot on the can lining-up with the mark on the tool, then turn the core 90 degrees and see if you get a response - if you don't then the core is for the *opposite* system the set is currently switched to, and you can mark the can "AM" or "FM" as appropriate!

A dual AM/FM ratio detector secondary core when detuned will give *two* points of heavy distortion with a clear undistorted region between them, and if you have to align by ear, set the RDT secondary core approx midway in the undistorted region.

*Don't forget to return the core to its original position afterwards!*

Coloured dots/marks on the base were mainly for assisting the factory girls in wiring the transforner in correctly, and if you wish to remove one to open it to replace tuning caps or identify windings, then good close-up digital camera piccies of the wiring prior to removal are a lifesaver! I wish digital snapperies had been around in my younger days!

Hope this helps a bit!

Chris Williams

8th Mar 2008, 1:06 pm	#1
RetiredHal Retired Dormant Member Join Date: Nov 2007 Location: Warrnambool Australia Posts: 41	IF Transformer Cans Hi, can somebody tell me how I can identify which adjustment slug belongs to which side of the IF transformer. Cct diagrams show both sides of the transformer to have a slugged coil. Access to these adjustments are from the top of the can and from the bottom (chassis/component) side of the can. I notice that most cans have a paint spot/ colour on one of the four connections. Does that mean something? Whilst I can identify the physical connections of the IF transformer and relate these to the cct diagram, I really have no way of identifying which coil slug bottom or top belongs to which side of the transformer as it is inside a sealed can. Hope the question makes sense? Cheers John

8th Mar 2008, 1:26 pm	#2
jim_jobe Heptode Join Date: Nov 2004 Location: Ripon, N.Yorkshire, UK. Posts: 782	Re: IF Transformer Cans According to the Radio Constructor, January 1949,page 470 the coil next to the chassis, i.e. the bottom one, should be the primary,connected to the anode of the preceding valve. The outer wire of the primary goes to the said anode, and the inner to HT+. The upper,secondary coil, outer wire goes to the grid of the following valve and the inner to AVC or ground. (See also RC May 1953, p 462.) Having said all that I'm sure there are exceptions to the rule, and we all know about Sod's Law! Jim

8th Mar 2008, 1:40 pm	#3
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,867	Re: IF Transformer Cans Hi! Unless the set-maker has specifically identified 'em on his repair words, there's no way of finding out except by dismantling the transformer and I'm sure you'd rather not do that! For alignment of a standard AM superhet it's not all that important which order you align the IF stages, but for FM and TV IF strips that need aligning to a specific order you really do need a full Maker's sheet rather than a Trader jobbie, which may have "howlers" in it, or a Newnes book page which might have only a circuit and nothing else! If you're adjusting something like a dual AM/FM transformer and have no data, use a trimming-tool with a clear mark on it, and mark a dot on the can lining-up with the mark on the tool, then turn the core 90 degrees and see if you get a response - if you don't then the core is for the opposite system the set is currently switched to, and you can mark the can "AM" or "FM" as appropriate! A dual AM/FM ratio detector secondary core when detuned will give two points of heavy distortion with a clear undistorted region between them, and if you have to align by ear, set the RDT secondary core approx midway in the undistorted region. Don't forget to return the core to its original position afterwards! Coloured dots/marks on the base were mainly for assisting the factory girls in wiring the transforner in correctly, and if you wish to remove one to open it to replace tuning caps or identify windings, then good close-up digital camera piccies of the wiring prior to removal are a lifesaver! I wish digital snapperies had been around in my younger days! Hope this helps a bit! Chris Williams