Dr. Z Maz 38-watt Senior guitar amplifier, made in USA, ser. no. R.5897, with a matching 2 x 12 Dr. Z 8 ohm speaker cabinet and a Z Air Brake power attenuator unit
Marshall PB-100 Power Brake Guitar Amp Attenuator White | eBay
Marshall PB100 Power Brake Inductive Speaker Attenuator | Guitar Center
Marshall PB100 Power Brake Inductive Speaker Attenuator
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Marshall Power Brake KILLS the THD Hotplate in this TEST - YouTube