Monthly Archives: October 2014

Vintage Engineering is Beautiful

EL84 output tubes in an EICO HF-81 integrated stereo amplifier.

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Sometimes you just have to build it yourself.

When a vintage component network goes bad and you can’t exactly go down to the corner store and buy a Sprague TC-24 anymore, sometimes you just have to build a new replacement yourself.

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Marantz 2270 Stereophonic Receiver Overhaul

I just had a great stereo receiver through the shop for repairs, the Marantz 2270. It’s the big brother to the Marantz 2245 I had through the shop a little while ago – mostly the same front-end circuitry, but with … Continue reading

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Use Copper Shielding Tape to Protect Dial Strings from Hot Tools [Tips and Tricks]

Dial strings are, quite frankly, about the worst things in the world. They’re usually a complex and finicky mechanical system parked right in the middle of an otherwise straightforward electrical project, and if a string breaks good luck getting it … Continue reading

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Toshiba 11H-540F Tabletop Transistor Radio Overhaul

I recently got to work on a little tabletop transistor radio from the late ’60s, maybe 1970 at the latest, from Toshiba: the 11H-540F. Not the catchiest name, but it was near the top of its model line-up featuring 11 … Continue reading

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Esteemed Bose® Model 901 Active Equalizer – Serial #230 Repair

Cross-posted from Rain City Audio: I had the distinct pleasure of working on one of the earliest  Bose® Model 901 Active Equalizers from Series I’s first production run. Serial #230, in fact! It’s made entirely by hand and shows traces … Continue reading

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HP 143A Wide Screen Oscilloscope Mainframe Restoration – Part 2

Part 1 I’m continuing to work on getting my HP 143A ocsilloscope mainframe fixed up as a dual-trace X-Y display. A lot of the time has been spent on reading and researching, but I’ve picked up an important tool that will … Continue reading

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Project Epsilon: Linear Regulated Power Supply from Spare Parts

Belgian engineering student Gert-Jan built a great looking, and functional, linear regulated power supply for a test bench from an old radio transformer and a handful of supporting parts. This is a pretty nice looking adaptation of the common LM317-based … Continue reading

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High Stability TCXO Upgrade for RTLSDR Dongles

Over at, I found out about a great new product that’s just come out for more precise SDR applications: a customized R820T-based stick with a high stability temperature compensated crystal oscillator (TCXO) in place of the stock crystal, giving … Continue reading

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Harmony H500 Solid State Guitar Amplifier Repair

And now for something a little different, this time it’s a vintage guitar amplifier: the Harmony H500. The owner sent it to the shop out of the cabinet to be serviced since it quit putting out any sound. It’s a … Continue reading

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