interesting interstage transformer idea

[edanderson]

maybe one of the varimu threads here has touched on this idea, but still worth posting:

http://www.philcoradio.com/tech/audio.htm

plan B basically uses a center tapped choke with the CT grounded to do the phase splitting.

ed

 

[Dan Kennedy]

Yeah, I first saw that in an old (40's) vintage jukebox amplifier.

Not a choke though, it's an autoformer.

 

[edanderson]

true, it is a center tapped coil (in this case the secondary of a transformer) connected as an autotransformer (with no isolation between signal input and output). though, i guess i've never seen an application of an autotransformer where some point in the center was grounded. likely there's another application for it though.

it would be unlikely to find a "choke" coil with a center tapped winding. maybe a CMR choke with two equal windings joined, though that would tend to be too small for interstage purposes. would any PA autotransformers have a tap right at the midpoint? i suppose a more readily available device would two windings of a multifilar transformer, connected as an autotransformer.

whatever the intended use of the original device, as dan points out, it would be connected as an autotransformer.

ed

 

[clintrubber]

Nice trick with a broad application area... it works for GHz's as well (on-chip coils) and why wouldn't it ?

Regards,

Peter

 

[emrr]

those examples are common in 1930's literature. nice to revisit them.

 

[mikep]

[quote author="edanderson"]
it would be unlikely to find a "choke" coil with a center tapped winding. maybe a CMR choke with two equal windings joined, though that would tend to be too small for interstage purposes. [/quote]

I tried an edcor wsm 600:600 wired as an autoformer. both windings in parallel makes it a single 150 ohm center-tapped coil. useful for line output step up, step down or inverting. IMO it is straightforward to implement global feedback with these kinds of circuits. I havent seen hardly any autoformers in relatively modern audio gear. there is the LA-3A sidechain, McIntosh power amps, and? anyone?

EDIT: actually it wouldn't be 150 ohms, rather 600 but with half the DCR.

mike p