Question on Output Transformer design, Voice of Music Model 160

[davohilts]

Hello,
I've been looking at using a chassis from the VOM 160 to build a 5E3 Deluxe circuit and have a question about the Output Transformer in the original VOM 160. There are the typical three wires on the input side to the power tubes but on the output side there appears to be two windings. One feeds the output to the speakers with the 4 ohm output not used. The other winding is a mystery to me. It connects to the second preamp tube cathode and the other lead goes to ground.
Can anyone help me understand what this winding does or what its purpose is?
I'm going to attach a copy of the schematic.
Thanks,
Dave

voice_of_music_160.pdf

[g1]

NFB winding?

[teemuk]

Can anyone help me understand what this winding does or what its purpose is?

It is simply another winding, with same or different turns ratio than in one which connects to speakers.

They use it for providing negative feedback to the phase inverter. Yes, NFB could be taken from the same winding that connects to speaker load as well, but this is where that "different turn ratio" probably matters since it has direct relation on magnitude of that negative feedback.

Given that there is 10K / 47R division I'd expect that the additional winding has quite high voltage. Perhaps a 70V/100V distributed speaker system winding, now repurposed for NFB takeoff point.

[davohilts]

thanks for the information guys!
looking at the actual circuit they have grounded the yellow wire and connected the green wire (shown going to ground in the schematic) to the cathode of the second preamp tube. I assume this doesn't make any difference.
I'm wanting to use this chassis for a Deluxe 5E3 build, do you see any issues if I just don't connect the other windings??
Thanks,
Dave

[g1]

The way they have connected the feedback winding determines whether the feedback is negative or positive. So if those green and yellow were reversed, it would probably go into screaming oscillation.
It should not matter if you don't use the feedback winding. You only need a load on the regular speaker output winding. Just tape off the unused wires so they can't touch anything.

[davohilts]

great, thats what I plan to do.
thanks a lot!
Dave