Monthly Archives: February 2016

Bose® 901 Series II Active Equalizer #68953 Repair

Posted on February 28, 2016 by jwk

This Bose® 901 Series II Active Equalizer was originally a European unit, designed for a 240V mains supply. Most if not all 240V equalizers with U.S. style plugs were sold on military bases in Germany and elsewhere, and returned with their … Continue reading →

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Bose® 901 Series II Active Equalizer #64364 Overhaul

Posted on February 27, 2016 by jwk

This Series II Bose® Active Equalizer came through the shop. It had suffered age-related failures in its electrolytic capacitors, and the resistors had drifted with age and moisture to produce the wrong curves. Fortunately, it’s nothing some maintenance can’t solve! … Continue reading →

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New Bench Storage

Posted on February 26, 2016 by jwk

Some pegboards, and wall mounting some parts bins, really cleaned up the benchtop!

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555 timer teardown (and a Retrovoltage drum trigger project)

Posted on February 23, 2016 by jwk

Ken Shirriff’s blog has a fantastic and detailed teardown of a 555 timer, the ubiquitous decades-old timer circuit that turns up in so many places: If you’ve played around with electronic circuits, you probably know the 555 timer integrated circuit, … Continue reading →

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Antique Radio Shop near Kunming, Yunan, China

Posted on February 22, 2016 by jwk

My friends over at Crimson Lotus Tea sent me this photo of an antique radio shop near Kunming, Yunan in China they ran into during a recent trip. They’re stacked to the ceiling in the shadows. Looks like a fun … Continue reading →

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Building the SSTRAN Part 15 Low Power AM Transmitter Kit

Posted on February 21, 2016 by jwk

Have a bunch of old tube radios, but nothing good on the air in your area? That’s a common problem, and SSTRAN has the solution! I just built one of these to give as a gift, and thought I’d write up … Continue reading →

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Bose® 901 Series I Active Equalizer #6878 Repair

Posted on February 20, 2016 by jwk

This early-production Bose® 901 Active Equalizer came through the shop recently for a repair. These Early models were the very first production run, back in 1968, and have a pretty significantly different circuit design from the later models, and feature … Continue reading →

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Retro 1956 Cyclometer VTVM – Hycon Model 615

Posted on February 19, 2016 by jwk

A pretty cool, very rare piece of test equipment turned up on eBay recently: a 1956 Hycon model 615 AC/DC VTVM. This was a precursor of today’s digital, using analog servo circuitry to drive the numeric digit display. These were … Continue reading →

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Building a Better Voltage Regulator

Posted on February 17, 2016 by jwk

Glancing through my feeds, I stumbled across a note on The Paleotechnologist describing a new replacement for the venerable LM7805 linear regulator IC. It turns up in a ton of devices, pretty much anything with a medium-current 5V rail including … Continue reading →

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Bose® 901 Series IV Active Equalizer #253288 Overhaul

Posted on February 16, 2016 by jwk

This Bose® 901 Series IV Active Equalizer came through the shop for a full overhaul. Inevitably over the years, various parts wear out and degrade and can make the equalizer sound bad – or not work at all. Without the … Continue reading →

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