[sdiy] sort of OT: The virtues of solid state bridge rectification vs. tube half-wave rectification

[Tom Corbitt]

The sag can be replicated by adding a resistor in series with the SS
diode. As current draw increases, the voltage across the resistor
increases, in effect stealing it from the tube. You'll need a beefy
power resistor, some people claim that wire wound are better for this
(with the added inductance) but I've used sandstone ones before and
variable tap ones with good results.

You'd need to pick your load lines and the amount of sag to size the
resistor wattage, or just start with something from the junkbox in the
50-200 ohm range (high = more sag) with a rating of at least twenty
watts.


Tom C



On Dec 4, 2007 6:03 PM, John Mahoney <jmahoney at gate.net> wrote:
> Tube rectifiers will exhibit "sag" when there's a big current draw.
> In a guitar amp, hitting a chord hard (with the amp's volume up) will
> create a big need for current, briefly pushing the rectifier into a
> sagging condition and thus causing more distortion in the amp. In
> extreme cases it's like the amp's response is spongy because the
> impact is gone.
> --
> john
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