Re: Solid State

Hi Alan,
         On the cores:
> Yes but Farnell (the only suppliers I've found for these) only stock
> little dinky ones in 3F3. 

That'd be the EFD (extra flat design) cores yes? Ungapped, they 
have quite a high initial permeability so you don't need a huge
number of turns to generate switchmode type inductances. I wound
a pushpull transformer on one of those which consisted of a 3+3 turn
bifilar strap primary (one strap on top of the other with insulation
between the straps and co-wound) and about 120 turns of Litz 
for the secondary. I think that was using a EFD25 core from memory.

> By the way Malcolm that was an excellent article in Wireless World - 
> you really crammed a lot in. 

Thank you. I'd actually written it in two parts as I couldn't see how
to make it one and keep within the magazine's criteria. They did a 
nice job of reducing it down. For the benefit of anyone reading it, 
I'll give a short list of errata (it was written before I'd joined 
any lists) :
(1) The equations I gave for terminal capacitances are incorrect (as
    I've learned from Bert, Ed Harris and others).
(2) The output voltage equation was a synthesis I attempted and 
    should have left out (invalid for limited energy Cap discharge)
(3) I forgot to mention grounding the secondary for the coupling check
(4) Some of the construction techniques I included are rather 
    primitive compared to the excellent information posted by Richard 
    Quick and there are obvious defficiencies in the simple gap design
    I wasn't aware of at the time of writing.
I think otherwise it's stood the test of time reasonably well.

Regards all,