Homebrew Toroidal Output Transformer

[smoking-amp]

Outside of buying a progressive toroid winder machine, $$$, I think using "long E" laminations (used for constant V xfmrs) makes for the best DIY approach for a high performance OT. Size the lams for dual standard bobbins, symmetrical P-P winds, low leakage L of a toroid, low capacitance of a progressive wind, easy winding, and low sensitivity to DC imbalance of an E-I design.

Magnetizing current distortion (transformer distortion source) can be eliminated by positive current derived feedback from the output tube cathodes
( low R current sense resistors, below cathodes ) back to the driver stage cathodes with a high R. Adjust feedback level to cancel out the primary winding resistance and output tube Ra (negative resistance effect).
Patent # US4614914 also RDH4 page 354, references dating from 1950.
A few resistors replace expensive lamination material and silver wire. You even get a higher speaker damping factor.

 

[tjerneld]

Hi,

bifilarly winding the primaries always will lead to large winding capacitance unless it's an unity coupled transformer according to F. McIntosh. You'd better wind only one wire at once.

Use the Quad II concept. 10% of the primary winding on the cathode and 90% on the the anode.
Bifilarly winding only for cathode windings.
(Quad II does not make use of bifilarly winding, but the cathode windings are close together).

 

[tjerneld]

For EI transformers, will winding secondary in bifiller reduce current capacity?

Dynaco Stereo 70, use bifilar wound secondary winding. Has no effect on current capacity.

 

[50AE]

Just a hint-reminder. Bifiliar (wire-to-wire) capacitance issue occurs only when anti-phase voltages are across both wires. In-phase voltages give no capacitance, in such way work bifiliar interstage 1:1 transformers.