UPDATE: Sold to David in BC.
Folks, this is the nicest GFA-555 II I’ve ever restored. What a beauty! The previous owner was a cellist for the Milwaukee Symphony Orchestra, who took excellent care of it. Cosmetically, it’s about as close to mint condition as they come. There are a few small ticks in the finish here and there, which I’ve touched-up, and are hard to notice, and the face is totally perfect! Click on the photos to see it in high-resolution.
Since this one is so nice, I pulled out all the stops and installed every enhancement I know for Adcom amps. This is the best one I’ve ever done! It’s got the 14ga power cord, new supply capacitors, and the improved power-supply layout. As you can see, I got really fussy about the neatness of the wiring in this one.
This is a thorough refurbishing! I want all my amps to last another 30 years. All electrolytic capacitors have been replaced with audio-grade types from Nichicon, WIMA or Panasonic. Even the big power-supply filter capacitors are new, something many restorers leave out, or charge extra for, because they are expensive.
Features:
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- Improved power-supply layout shortens wires and reduces clutter and radiated noise.
- Transistors in the critical input stage are matched for gain. This step is important to assure low DC offset at the output, and low distortion.
- Local power-supply bypass capacitors added to the input board for greater power-supply smoothing.
- AC noise-snubber capacitors added to bridge rectifiers.
- Driver transistors changed to 180V 2SA1492/3856 for greater voltage headroom. The originals are 140V parts, and are known to fail when driven hard at high-frequency, due to the power supply swing of 170V.
- Output transistors are original; the very excellent Toshiba 2SD424/554. This is a particularly well-matched set from Adcom.
- Circuit boards are cleaned and all solder joints are re-flowed and inspected.
- New power switch and spark-supressor capacitor. (Most Adcoms do not have soft-start circuits, and are hard on power switches.)
- New, sealed Bournes bias trim-pots.
- Heat sinks added to the Class-A driver transistors for greater reliability.
- Dale LVR 1% 5W emitter resistors replace the original 5% sand-cast resistors.
- 50A bridge rectifiers.
- High-temperature and high-endurance capacitors used throughout.
- 14ga Power cord with heavy-duty plug.
- New gold-plated RCA input jacks and binding posts.
I measured 260WPC at 8 ohms and 340WPC at 4 ohms just before clipping.
Sound quality is clean and smooth as expected with the studio monitors, and it drives my subwoofer like a beast! Amazingly strong and tight bass.
Heatsinks are attached to driver transistors, as these otherwise run extremely hot and are known to fail.
Bournes sealed trim-pots for bias.
Also, I’ve removed the 8 wire-wrapping posts and soldered the wires directly.
I made them out of solid 6ga copper wire, and soldered large terminals to them.
The new supply capacitors are physically smaller than the originals, so I was able to improve the layout of the power supply. Originally, the bridge rectifier is mounted on a heatsink on top of the capacitors, where they dump their heat into the capacitors. Moving the bridge to the traditional location means better heat-sinking.
I often discover that the original electrolytics in this position are exhausted, and show high ESR. The Panasonic ED is a terrific replacement. It’s a high-temperature, high ripple-current and high-endurance capacitor, and I am using a 250V capacitor in an 85V application for even more reliability.
If you prefer, I can install an IEC or Neutrik Power-Con power inlet for $125.
Personally, I prefer hard-wired power cords, as it’s one less physical connection.
Contact me here if you’re interested. Thanks!