Category Archives: Bose

Everything to Know about the Bose 901 Series IV Speakers & Active Equalizer Repair

Posted on August 10, 2026 by retrovoltage

A detailed look at the Bose 901 Series IV speaker system and Active Equalizer, with a brief history and explanation, plus repair tips and tricks, schematics, a discussion of the 5 different Active Equalizer versions for this generation, and a parts list with direct links to buy. Continue reading →

Posted in Audio, Bose, DIY, Electronics, Hi-Fi, Stereo, Vintage | Tagged , , , , , , , , , , , | 4 Comments

Everything to Know about the Bose 901 Series III Speakers & Active Equalizer Repair

Posted on July 31, 2026 by retrovoltage

A look at the Bose 901 Series III speaker system and Active Equalizer, with a brief history and explanation, plus repair tips and tricks, schematics, and parts list with direct links to buy. Continue reading →

Posted in Bose, Electronics, Hi-Fi, Stereo, Vintage | Tagged , , , , , , , , , , , , , | 4 Comments

Everything to Know about Bose 901 Series I and Series II Active Equalizer Repair & Speaker Systems (and the 800, too!)

Posted on June 12, 2026 by retrovoltage

A deep dive into the history and repair of Bose 901 Series I and II, plus the Bose 800, sourced from direct experience repairing more than 500 Active Equalizers. Includes vintage ad copy, photos, tips and tricks, schematics, and parts lists. Continue reading →

Posted in Audio, Bose, Collections, Resources | Tagged , , , , , , , , , , , , , , | 9 Comments

Bose® Active Equalizer Test Platform

Posted on April 13, 2016 by retrovoltage

Looking for the latest info on repairing your Bose 901 Series I, Series II, or Bose 800 Active Equalizer and speaker system? Take a look at the latest in-depth guide with everything you need to know (and more!) This project … Continue reading →

Posted in Audio, Bose, DIY, Electronics, Stereo, Test Equipment | Tagged , , , , , | 3 Comments

What do we have here?

Posted on December 1, 2015 by retrovoltage

I was reading about how to build a capacitor checker from the December 1959 issue of Popular Electronics and stumbled across something that looked very familiar. I know that shape. Nearly identical to a Bose® 901 Series I/II cabinet, and even … Continue reading →

Posted in Audio, Bose, Collections, Commentary, DIY, Electronics, Vintage | Tagged , , , , , , , , , , , , , | 2 Comments

Bose® 402E Active Equalizer #102853 Repaired

Posted on November 30, 2015 by retrovoltage

The first Bose® 402E Active Equalizer, for the Panaray speaker system, just came through the shop. It’s a small speaker array system, designed around similar drivers in the 901, and uses an Active Equalizer for the same effect. They’re designed … Continue reading →

Posted in Audio, Bose, Electronics, Projects | Tagged , , , , , , , , | 7 Comments

1937 Zenith 5-S-126 Tune-Up

Posted on October 30, 2015 by retrovoltage

This very nice Zenith 5-S-126 came through the shop a little while ago. It was originally purchased by a local collector from eBay already restored and playing, and served well for a couple of years, until it started having some … Continue reading →

Posted in Audio, Bose, Projects | Tagged , , , , , | 6 Comments

Bose® 901 Series VI Active Equalizer #199732 Repaired

Posted on February 20, 2015 by retrovoltage

A first for my shop, I recently worked on a Bose® 901 Series VI Active Equalizer! These are considerably newer than the Series I-IV that typically come through the shop, although they’re still getting to be 25+ years old at … Continue reading →

Posted in Audio, Bose, Electronics, Projects, Vintage | Tagged , , , , , | 1 Comment

Bose 901 Series IV Active Equalizer #241792 Refurbishment

Posted on November 3, 2014 by retrovoltage

Looking for the latest info on repairing your Bose 901 Series IV Active Equalizer and speaker system? Take a look at the latest in-depth guide with everything you need to know (and more!) Bose® 901 Series IV Active Equalizers are … Continue reading →

Posted in Audio, Bose, Hi-Fi, Projects, Stereo, Vintage | Tagged , , , , | 1 Comment

Bose 901 Series I Active Equalizer #50911 Repaired

Posted on December 3, 2013 by retrovoltage

Looking for the latest info on repairing your Bose 901 Series I, Series II, or Bose 800 Active Equalizer and speaker system? Take a look at the latest in-depth guide with everything you need to know (and more!) I recently … Continue reading →

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