Tube Guys, What Is Going On In This Mesa Amp?

[Cyberdragon]

This circuit is nuts, I'm not sure he's 100% drawn it correctly though. There is a tube in there who's only connections to the system are a capacitor to the grid and a resistor to the cathode both tied to the input, and a capacitor and resistor in series on the plate as output. That it, 0 DC bias at all. Both sides ultimately tie to ground though resistors so the only source of voltage even on the other side of the caps seems to be resistor drop, which can't be very much since the cathode side ends up positive, and the anode side negative in terms of where the resistor dividers terminate (as he says similar to a cathode follower, but even that has to have plate bias). Has anyone seen a circuit like this before and how does it even work?

[floobydust]

I've worked on the Mesa, the schematic is incorrect (on purpose), I have it redrawn somewhere.
They have a mystery wire called a "radiator". It's a wire connected at one end to an O/P tube's plate and 220k resistor. At high output power, the plate-wire radiates due to the high voltage AC and causes positive-feedback via capacitive coupling to make the amp wail and have other special fx. I wonder if he noticed it.

[Cyberdragon]

I've worked on the Mesa, the schematic is incorrect (on purpose), I have it redrawn somewhere.
They have a mystery wire called a "radiator". It's a wire connected at one end to an O/P tube's plate and 220k resistor. At high output power, the plate-wire radiates due to the high voltage AC and causes positive-feedback via capacitive coupling to make the amp wail and have other special fx. I wonder if he noticed it.

Ok so the circuit is still really weird but at least it has a proper power supply. No laws of physics are being violated.

By "radiate" do you mean like RF? Corona discharge? Heat?

[floobydust]

I'm not sure if it's common knowledge but it had me stumped for a bit to find a wire from a plate simply ending near the pre-amp section, connected to nothing.
That's what they are called because the wire "radiates" like 400Vpp at audio frequencies, as a gimmick capacitor with HF rolloff due to the 220k series resistor, in proximity to the sensitive pre-amp section.
Normally it does nothing but as soon as amplitude goes up and waveforms are a bit more square, there is some positive feedback and the amp's sound goes to a new dimension.

The video I'm not clear about what is the odd circuit he found, you don't need formal grid bias if you use "space-charge" instead. It's likely doing that, and when the adjacent triode upsets the space-charge then you get extra effects.

Musicians want a unique sound and get their amplifiers modded so no one else can sound like them.