Mesa has a few amps [ they don't seem to do it anymore ? ]
where they drop the B+ and call it sponge or something
anyone know, is that a simple power resister ?
Re-amping Phatt style
Hi, the problem with dropping the B+ voltage is that the power tubes require a different bias. I have a 50 watt Marshall clone that is switchable between tube rectifier/32uf filter & solid state rectifier/64uf filter. The B+ voltage difference is 446V (tube rectifier) & 472V (solid state rectifier). This requires that a 15k resistor be switched into the AC side of the bias circuit in tube rectifier mode to maintain the power tube bias at the same % of plate dissipation in both modes. I believe power scaling adjusts the bias voltage also, to maintain correct bias (though I haven't read up on much). You can use a "sag" resistor that drops voltage across it dependent on current demand, maybe this is what you are thinking with Mesa. It is usually done to mimic the effect of a tube rectifier's sag. It is usually a wire wound resistor of sufficient wattage. Hope this helps. Cheers