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

Bruce Collins at Mission Amps tells me the Chicago 32-20 amp is selling
extremely well. Players are buying it for the warm crunchy tone and great
features you can’t find on any other amp. You can switch the amp from fixed
bias to cathode bias which changes the texture of the tone. You can use the
DEEP switch to fatten your sound, like the loudness switch on old Hi-Fi
gear. Another switch disables the cathode bypass capacitor. All these
adjustments allow you to tailor the basic circuit design of your amp to your
own tonal tastes.

Players are also choosing the Chicago 32-20 amp because of its tremendous
value. At only $999 it is hundreds less than other amps in its class. Every
Chicago 32-20 amp is hand-built by a master amp maker who is known worldwide
for tone. Bruce uses only New Old Stock (NOS) military-grade paper in oil
tone capacitors and solders every part himself.

When the amp was being designed, special attention was paid to the
rectifier. The copper solid state rectifiers were tried but discarded in
favor of real tube rectifiers. The copper solid state rectos deliver
slightly more B+ voltage with less sag, which is why they give the
impression of “tightening up” the sound, or making an amp sound more
“crisp.” But that is at the expense of real tube sag and the warmth it
provides. It would have compromised the true vintage tone of the amp. The
rectifier tube is one of the tone generating components in a vintage tube
harp amp, and solid state just doesn’t cut it.


-Rick Davis
The Blues Harp Amps Blog

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