Ferranti AF-5 construction

Seeing as I had an open secondary winding I decided to have a look inside the casing ,
What I found is a bobbin composed of three concentric cylinders  made of chemically hardened  rubber, its held up remarkable well for something approaching 100 years old  , Primary next to the core and outermost , secondary in the middle .Outermost primary winding is divided into three spaced sections side by side .

The unique thing about the bobbin structure is once I get the lams out and desolder the hook up wires it comes apart into 1/2 primary ,secondary and other half primary ,so I can rewind only the secondary section that needs attention without having to demolish all the other sections  in the process , thats quite a neat feature .

a quick preliminary measure of the primary inductance with the LCR showed in the region of 110 hy at 100hz but drive is only a couple of hundred millivolts .

Cool, I've wondered about those older UK Ferranti. 

hopefully the scan does justice ,

Three different widths of lam , thinner at the outsides as the bobbin window is circular .

you can also see the little protruding stubs which form the divisions ,everything is 'air spaced' from everything else .
four sections on the secondary winding .

I think I must have inadvertantly stabbed the outer 1/2 pri  coil with the edge of a lam while dismantling , its open circuit now  :-[
If you are dismantleing  one of these be sure to put extra tape around the the very thin outer textile wrap as it tends to catch while you extract the lams one at a time ,
Oh well , live , learn ,pass it on , ;D

Its not a dead loss , everything is reusable at least . I might look at winding it as an output transformer rather than interstage .

I feel I should at least try and properly document this transformers finer details in the form of a winding sheet ,
Maybe CJ ,you might have a template for that somewhere ?
I can  get wire gauge, dc resistance and mean turn lenght for each of the bobbins sections easily enough ,I may also be able to unwind and count a segment from each drum.

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