Advantages of tertiary feedback winding

[PRR]

> advantages of a tertiary winding is that you can pass dc through it if the transformer is gapped.

Same as any other winding?

Also the need for DC in the NFB loop is designer's choice. If it returns to a grid the DC is dang-near Zero.

We often choose not to buy an extra grid for NFB, returning to a Cathode which has some DC. However 1mA in an 8-Ohm winding on a Power amplifier is typically "no" DC in the core. Actually far less than typical plate-winding DC. Even if "balanced" there's 3mA-30mA unbalance between two tubes, and this runs through 30 times more turns than a speaker-impedance winding.

If you must get Damping Factor much below 10, you need to tap NFB from the load winding.

If you need to connect load to any long strange mess of wire, you probably want an added winding just for NFB, so the load can float where it will.

Those of us who live all in one room/suite will probably avoid a Tertiary because it is added cost and complication.

 

[CJ]

using a center tapped feedback winding can give a circuit designer some flexibility,

if you tap the speaker winding which usually has one end grounded to the chassis, then you only have one lead to play with,

if you use a FB winding with a CT, then you have two leads to play with, ref the CT to ground, and then you have + and - FB,  plugs into the balanced Pultec circuit,

Fender and Marshall plug a one lead system into the phase inverter to get neg FB,

no phase inverter in the Pultec, just an HS-29 innerstage xfmr,

there could be other reasons to use a FB wind, when you have a lot of current flowing through a winding, you get 2nd order distortion caused by the DCR of the winding, so if you keep the AC current low in a FB line, you might have a cleaner system, interesting to check this on the scope to see any difference between a tertiary FB wind and a speaker FB line,

 

[alexc]

Thanks so much for the tutoring

Unless I get some nice vintage traffos in the near future,  I'm going down the Hammond 1645 path and use it's tertiary feedback winding.

I'm looking to try a bunch of new things in this, my next pp tube build.