Wednesday, December 8, 2010

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 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.

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