Saturday, 17 April 2010

IFT Vindication

Last week's hunt around the junkboxes at the NARSA Rally for IF Transformers with Roy, gm4vki, was fruitless - except for a single Denco IFT11/10.7 (which - although I can find no data on the 'net, doesn't measure as if it is a 455kHz unit). However, Roy spotted an old domestic radio chassis in the bring-and-buy section, which I snapped up for a fiver. I gave myself a twinge in the shoulder lugging it back to the car!

I've now stripped out the chassis...



which yielded a fine harvest - fully enough to justify both the fiver and the shoulder. Some of the parts are of 1940s vintage and the set carries no obvious makers name and evidence of a lot of repair/modification.

Amongst the goodies to be harvested were the main HT transformer and a nice choke (these gave me the shoulder problem!) and the reason Roy spotted and I purchased the chassis - two IF Transformers...



On robbing out the IFT's from the chassis, one of them spilled it's innards from the can (I was intending to be very careful in disassembling the IFTs - but it came apart in my hand - honest, gov!...



Readers should understand that this was the first kosher IFT I'd ever had in my hand - all previous units were my own homebrew efforts (Blogs passim)!

First thing to delight me was the spacing between the coils - which was the same, staggering wide-open space that had shocked and surprised me in the development of my own h/b trannies. I still find it amazing that there is such distance between the coils for "critical" coupling. Second delight came when I hooked up the units to my wobbulator.



The response of these commercial IFTs was really no better than my homebrew efforts...

The measurement suggested that these units were...

1) under-coupled
2) better than my efforts with coils wound on sewing-machine bobbins

but, joyfully,

3) not as good as my final units with coils made from axial chokes

I am delighted to conclude that my IFTs are not the Achilles' Heel of the not-so-superhet receiver project I once suspected they were!

...-.- de m0xpd

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