Unusual Zenith OPT Amp 4k21

[Joe Willis]

Hey!

I'm putting a new circuit in an old amp. a zenith 4k21 console pull. it's a SE 6bq5 amp, but the output transformer has an additional tap, I think it was used for some sort of filtering on the original circuit. the primary leads are red brown and blue. Can I just tape off the brown and use it as a regular old SE OPT? Tech preservation is down so I can't get my hands on the schematic right this min. I think it should be fine but I just like to check with you all when I come across something new to me.
Thanks as always!

 

[mashaffer]

Does it look something like this...

It could be a hum bucking tap. Note how the wiring is backward from what an UL connection would be. I suspect that you could leave the hum bucking tap unused but I would wait for someone more experienced to chime in.

 

[Joe Willis]

Yup, that looks about right. I haven't checked the resistance between leads to know that it is the brown lead that is doing the bucking, looking at the schematic it looks like red that wouldn't be used. is that a zenith circuit?

 

[Tom Bavis]

With enough filtering, the tap is unnecessary. I think the tap cost less (and of course too less chassis space) than an extra filter cap.

 

[mashaffer]

This one is from an RCA. I would think that the brown would be the one not to use. On the other hand I wonder if there is any downside to going ahead and using the hum bucking coil for your project. ???

mike

 

[Joe Willis]

Probably not but I have already added a choke so it would be kind of redundant. Kind of a cool idea. I like the way they were able to cut down on some iron or at least a big cap.

Thanks guys.