This other Flyback Protection..

[leadfootdriver]

Instead of 3-1KV Diodes like in a TW, there's 1-3KV, cool. But then there's the addition of a 47pfd Cap across it.
What does the cap do in this arrangement?

[trobbins]

Depending on the actual amp, the anode voltage can 'fly' around quite wildly under certain playing conditions, as only stray capacitance both inside and outside the output transformer limits the voltage excursions (simply described by the transient energy equation I = C . dV/dt). Adding extra capacitance could slow down the voltage transient waveform. Too much capacitance and it starts to roll off the treble response.

Imho there are better ways now to provide output transformer protection, but old habits die hard.

[leadfootdriver]

Thank you.
Everything I could find pretty much reflects what you said except for the rolling off of the high end.
Electronic Forums talk about using a FBD on Motors or Solenoids..

[GAStan]

.
Electronic Forums talk about using a FBD on Motors or Solenoids..

I've used these on DC solenoids and relays. In fact Dumble has them on the relays in his amps.

The coil of the relay/solenoid when energized has a magnetic Flux field built up in it. When it is suddenly de-energized this field collapses causing a reverse polarity voltage spike. The diode, which is parallel to the coil and reverse biased during normal operation of the coil, is forward biased by this spike so the spike is shunted and kept to the forward bias voltage level of the diode, preventing damage to other components that might be in the same power circuit.

I am unfamiliar with their use on motors.