GFA-565 monoblock amplifier restoration
Note: This issue also may similarly apply to the GFA-585
This information describes what two people have done to restore GFA-565 monoblock amplifiers. A typical problem that happens over a decade or so of use with these amplifiers is that some of the capacitors will leak electrolytic fluid onto the printed circuit board that can create a large DC offset that potentially can damage speakers or the amplifier.
The printed circuit boards are made of paper, not fiberglass, which tends to absorb the leaky electrolytic material. The cleaning job requires soaking and washing of the printed circuit board repeatedly as well as removal and replacement of some components to get in to difficult areas. Our service technician says he uses dish soap and soaks the printed circuit board (due to the paper), others report they use a variety of solvents. Also, suspect capacitors that have caused the leaks or may leak in the future are to be replaced. DC offset must be verified to be low (well under 100 millivolts).
GFA-565 #1 “seller of rebuilt amplifiers on eBay”
Wrote the following:
Fully re-built and tested, these amplifiers have had a complete teardown, re-component, re-certification, style restoration and function perfectly.
Because of the highly specialized front end of these amplifiers, ALL 565's have the same problems. Thinking of buying a used one that isn't fully rebuilt? Well, you WILL have problems with it because EVERY Adcom 555II, 565 and 585 suffers from the same type of problem. And that usually shows up as blown fuses and a burnt speaker on one channel-why take a chance?
The ONLY way to insure longevity in these amplifiers is to:
1)Completely remove all components from the circuit board, wash both sides of the board with alcohol and acetone.
2)Install all new parts including, matched low noise metal film resistors, new capacitors, new transistors, custom gain and noise matched transistors for the front end and then
set up to specs.
3)And just for the heck of it, I install genuine Solen Chateuroux capacitors in the front end, replace the input wires with one strand of 30 gauge long crystal, 99.995% oxygen free pure annealed copper, and I installed brand new RCA jacks.
•As you can see by the before shots, these amps were in a dusty environment.
•All the output transistors are the original factory certified matched sets.
•They have been pulled and tested on the curve tracer and exhibit no leakage.
•The mains capacitors have been pulled and ripple tested and are fine.
•The transformers have been ring tested for abnormalities and are OK.
These amps function perfectly and perform to ADCOM specs. A lot of time and care went into these 565's. Why? Because I love what I do and I like Adcom products.
I have been repairing Adcom since the GFA-1 and have been a fan of their designs for 20 years. Why buy an Adcom that has one foot in the grave? These are completely rebuilt and tested.
Loading...