Reviving loft luggage

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?