Is this capacitor required?

[ygg-it]

I see in pretty all old tube amplifiers the capacitor across the transformer, which is nearly disappeared in new schematics.

Why?

 

[Vincent77]

That capacitor cuts high frequency signals and transformer resonances. I see it mostly in guitar amps, where it reduces harsh distortion.

It should not be needed in modern HiFi designs.

 

[JonSnell Electronic]

I have been repairing valve power amplifiers for many years and cannot think of a single commercial guitar amplifier that has snubbing capacitors across the load like described in the circuit diagramme. Old valve audio stages in televisions used that design to remove sibilance however.

 

[DF96]

You will sometimes see it in old radio sets too. In the 1950's most folk had never heard hi-fi and found treble rather alarming. AM radio doesn't have much treble anyway, and the loudspeaker/cabinet of the typical radio would be a mass of resonances up there so better to suppress treble than reproduce it badly.