Re: [Harp-L] Re: The Mission Chicago 32-20 harp amp

Jim, the sag circuit in the copper solid state rectos is (as I understand
it) a power resistor.  It attempts to emulate the sound of real tube sag,
but it does not sound the same.  Tube sag is a kind of living, breathing
effect that varies with volume and attack and load on the amp.  It is one of
those things that makes good tube harp amps seem to be alive.  Artificial
sag (from a static resistor) sounds rigid, the same at low volume as as
higher volumes.

I've used the copper solid state recto in several amps, and I liked it in
smaller class A amps like my Champ.  But small amps like the Champ don't
really produce sag, since they are always cookin' on high anyway.  The solid
state recto gave the Champ a crisper feel.  "Crisp" and "sag" are opposites
of each other as far as rectifiers go.

-Rick Davis
The Blues Harp Amps Blog

On Fri, Dec 10, 2010 at 3:37 PM, Jim Rossen <jimjimdr@xxxxxxxxx> wrote:

> I disagree with this analysis of Weber Copper Cap rectifiers. Copper
> Caps are actually a line of rectifiers that have different b+ (power
> supply) voltage and sag (the fall in b+ when the amp is presented with
> a strong input signal) characteristics- from none to lots depending on
> the model chosen.  This is similar to tube rectifiers, for example-  a
> GZ34 tube recto provides higher voltage and less sag than 5U4 which
> provides higher voltage and less sag than a 5R4.  So... a Copper Cap
> can provide less, more or about the same sag as a particular tube
> recto, depending on the one chosen.  The exception to this is with a
> solid state recto with no sag circuitry- which will provide high b+
> and no sag compared to about any tube recto setup (but perhaps
> parallel GZ34s).
> The trade-off of characteristics associated with different b+ voltage
> and sag characteristics (loud/crisp/tight vs warm) occurs with
> different tube rectos AND Copper Cap rectos.  (BTW- b+ with lower
> voltage and more sag can be produced without changing the recto by
> inserting a power resistor between the b+ source and the first filter
> cap)
> Was the message below directed at Gary O's recent posts regarding the
> use of Copper Cap rectos in the Cruncher?  Does a 1961 Fender Concert
> solid state rectified amp lack tone?  I am pretty sure the Harp King
> is SS rectified.
> Jim R

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