Fisher KX-200 Restoration Highlights
Background
A customer saw how shiny the amplifiers looked that we were selling, and contacted us to see if we could make his old tarnished amp glow like the ones we were offering. He sent in his amplifier, and we immediately noticed it had been previously worked on, as a few of the capacitors had been replaced. The customer reported he had sent it in not too long ago to a well known shop in his area, and that it had cost him an arm and a leg and left his dissatisfied in how the amp sounded. We signed him up for a Gold Level restoration, and got to work.
Restoration Procedure
The original transformers, knobs, and face plate were carefully removed from the chassis. The entire amp was ultrasonically cleaned in our immersion tank. This unique method of immersing the entire unit in an ultrasonic cleaner using a proprietary cleaning solution gives remarkable results. Not only was the chassis cleaned of corrosion, but all the parts are cleaned inside and out— including tube sockets, input jacks, speaker terminals, controls and switches. Even the wires and solder joints came out shinning like new and free of corrosion.
After ultrasonic cleaning, the KX-200 was dried in a special temperature-controlled dehumidifier overnight. Then the chassis, knobs, and face plate were hand polished to an incredible shine. The result is an amp that is literally like-new, without all the corrosion on the chassis, tube sockets, switches, and jacks etc. that reduces the performance and reliability of vintage electronics.
After that we re-assembled the amp and begin the electronics repair/restoration. The power supply was modified to optimize performance with modern high performance filter capacitors with a 200% increase in reserve capacity. All coupling and bypass capacitors were upgraded to high quality “audiophile” types, with each hand selected for optimum sound quality in the circuitry. This is where the previous company had really failed to service the amplifier, having only replaced the filter capacitors and nothing else. There was also a very “patchy” fix done to the volume control, which we rectified.
Next the driver balance and bias was critically aligned using a spectrum analyzer. The use of a spectrum analyzer instead of a simple distortion analyzer allows not only for more accuracy than the traditional “service manual” methods. It also allows the “nulling out” of odd order harmonics, especially the 7th and 9th order harmonics which are the ones that contribute most to harsh and fatiguing sound quality.
The overall result is an amplifier that looks and sounds as good as modern technology allows.