Category Archives: Audio

KLH Transistor Substitution Guide (“Solid State Components Cross Reference Guide”)

Posted on October 6, 2026 by retrovoltage

This post contains the transcribed text of the Februrary 1970 KLH Solid State Components Cross Reference Guide (aka, transistor substitution guide), obtained from an original copy of the document. It’s in this format because it’s easier to search and find quickly. Continue reading →

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The Speaker Spotter — October 2, 2026

Posted on October 2, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. 1977 Klipsch La Scala $3,500 · Portland Someone’s … Continue reading →

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The Speaker Spotter — September 26, 2026

Posted on September 26, 2026 by retrovoltage

After a short hiatus while I sorted out some tech issues with automation that helps me create these posts, we’re back! The Speaker Spotter is a recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. … Continue reading →

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The Speaker Spotter — August 14, 2026

Posted on August 14, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. Some really interesting, highly unusual things in today’s … Continue reading →

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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 →

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The Speaker Spotter — July 31, 2026

Posted on July 31, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. klipsch la scala industrial split $2,300 · Eugene … Continue reading →

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1961 Audax CA-70 “Sonoteer” Speaker Refurbish

Posted on July 22, 2026 by retrovoltage

This set of 1961 Rek-o-Kut Audax CA-70 Sonoteer speakers got a full overhaul inside and out. Come learn about these interesting mid-century open baffle hi-fi speakers from a little known manufacturer and see how they turned out with detailed interior and exterior photos, and the original advertisement from September 1961. Continue reading →

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The Speaker Spotter — June 26, 2026

Posted on June 26, 2026 by retrovoltage

A recurring feature curating interesting speakers for sale on Craigslist from around the Pacific Northwest. Links to Craigslist postings might go down at any time if they’re sold or pulled from sale. We’re a little lighter this week with only … Continue reading →

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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 →

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HH Scott HHS-20 “Scotsman” Receiver Overhaul

Posted on January 27, 2017 by retrovoltage

A local repeat customer recently brought in his old HH Scott HHS-20 receiver for an overhaul. It worked a few years ago when he put it away, although not without a few issues of its own, and when he dug … Continue reading →

Posted in Audio, Electronics, Projects, Stereo, Vintage | 3 Comments