Author Archives: jwk

EICO Stereophonic Integrated Amplifier HF-81 Repair

Posted on November 7, 2014 by jwk

From the late ’50s, I had this nice example of an EICO HF-81 amplifier come through my shop. These are nice little stereo amplifiers with a built-in phono pre-amp and RIAA equalization and feature about 14W of power output per … Continue reading →

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Boes 901 Series IV Active Equalizer #241792 Refurbishment

Posted on November 3, 2014 by jwk

Bose® 901 Series IV Active Equalizers are getting up there in years now, too, so more and more are coming up for repair. This one came in with a flickering power supply in need of an overhaul. Series IV was … Continue reading →

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Vintage Engineering is Beautiful

Posted on October 30, 2014 by jwk

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

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Marantz 2270 Stereophonic Receiver Overhaul

Posted on October 26, 2014 by jwk

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]

Posted on October 24, 2014 by jwk

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

Posted on October 20, 2014 by jwk

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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HP 143A Wide Screen Oscilloscope Mainframe Restoration – Part 2

Posted on October 15, 2014 by jwk

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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Harmony H500 Solid State Guitar Amplifier Repair

Posted on October 10, 2014 by jwk

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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DIY Replacements for Vintage Couplets and Printed Electric Circuits

Posted on October 9, 2014 by jwk

Starting in the ’50s, they’d figured out how to start miniaturizing components. “Couplets” and “printed electric circuits” started showing up in equipment around then. These components were combinations of several resistors and capacitors in a single package. Like most components … Continue reading →

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Phase Linear 2000 Pre-Amp Overhaul

Posted on October 6, 2014 by jwk

I had a Phase Linear 2000 on the bench for a repair recently. It was running okay, but had some pops and clicks and the controls weren’t all that smooth. Time for an overhaul before anything worse cropped up! This … Continue reading →

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