Owner's Hot-Mods - Reviving loft luggage

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Reviving loft luggage

Printed From: Graham Slee Hifi System Components
Category: DIY AUDIO
Forum Name: Owner's Hot-Mods
Forum Description: Tell us how and why you hot-modded your audio gear
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=5683
Printed Date: 27 Mar 2026 at 5:06am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com

Topic: Reviving loft luggage

Posted By: Fatmangolf
Subject: Reviving loft luggage
Date Posted: 07 Jan 2024 at 7:56pm

I have been fortunate to hear the 7eventy stereo power amplifier. I slso enjoyed the visuals of the bias meters on the prototype unit. They inspired me to seek the Realistic amplifier power meter from the early eighties that I lodged in my loft in the late nineties.

The APM 100 is a passive unit that rectifies the incoming signal to drive an analogue meter for each channel. It is calibrated at 100 Watts full scale which is far more power than I use, even with magneplanar speakers 1 Watt is more like it so increasing the sensitivity was necessary. So was backlighting the meters...

I opened up the unit and found a circuit power on each meter which had a few more components than I expected. I had lost the manual long ago so downloaded it and found the schematic which saved me some time. A half-wave rectifier followed by a potential divider which I modified to get 10 Watts FSD. I soldered a 15k resistor on parallel with R3 and R4 and used a sine wave generator and AC voltmeter to recalibrate the meter of each channel. Added some LEDs under each meter (rechargeable PP3 powering a 3 LED 12 volt strip on each meter, reusing the 4/8 Ohm switch for on/off) and the APM 100 is back in action after forty years. What other loft luggage is worth reviving?

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Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.

Replies:

Posted By: Fatmangolf
Date Posted: 08 Jan 2024 at 7:32pm

A cold start to the morning changed my plans to focus on a boiler repair by British Gas. It did give me s chance to think about my kitchen cupboards and use of my counter tops. I also air fried some chinese style ribs with extra szechuan pepper in the five spice. Yum!

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Jon

Open mind and ears whilst owning GSP Genera, Accession M, Accession MC, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.