A confusing power tube configuration

[kagliostro]

Looking for 6BQ6 amp schematic I've found this



What is happening there ?? Those cathodes are connected to the OT secondary ........ ???????

Someone understand this configuration ??

I foud it on this page, but there are no info about the schematic

http://www.pcad-ok.com/saup/saup13/saup13-1.htm

Franco

[jazbo8]

What is happening there ?? Those cathodes are connected to the OT secondary ........ ?

It's just cathode feedback ("CFB") with the feedback winding drawn on the "secondary side", the OPT really does not care where the winding is located - since it's always in the magnetic path anyway. But commonly, the CFB winding is drawn on the "primary side" to denote its function.

[shooter]

just cathode feedback

I can *sorta* see that, since the taps are at the *ends* of the windings - where the tubes would see outta phase signals, but, why ground the 4ohm tap?, wouldn't that *float* the zero tap asymmetrically??

[jazbo8]

I should amend my earlier post, in this particular amplifier, the OPT does not have a dedicated CFB winding - to save money no doubt - so the designer just used the secondary/speaker output taps for the job. The 4 Ohm tap is grounded, because it is exactly half way between 16 Ohm and Com (or 0), so by grounding it, it serves as a center tap to allow symmetrical cathode feedback for each half of the push-pull output pair.

[kagliostro]

Thanks Jazbo8

What you say remembers to me some schematics from Menno Van Der Veen I've seen long time ago



Thanks again

Franco