Re-amping Phatt style

Tube or solid-state, this section goes to eleven!
User avatar
okgb
Diode Debunker
Information
Posts: 768
Joined: 16 Mar 2010, 03:58
Has thanked: 226 times
Been thanked: 38 times

Post by okgb »

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 ?

User avatar
ivan H
Breadboard Brother
Information
Posts: 64
Joined: 29 Sep 2012, 05:21
Been thanked: 10 times

Post by ivan H »

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

Post Reply