This is a Harman-Kardon receiver I built from a kit in 1964 for a High School Electronics shop class. This receiver cost $250 in kit form in 1964.
The cabinet is one that I made in 1973 from solid walnut. This cabinet is not the one Harman-Kardon sold for this receiver.
The receiver has been electronically restored. I still have the assembly manual and schematic making it easy to work on.
Several years ago my parents gave me this receiver when they purchased a new system. It actually played pretty good, but I decided that a full restoration was in order. There is really not much damage or wear on the receiver except for the normal wear for a receiver that is 40 plus years old. The first and most challenging restoration challenge was to restore the dial glass after my failed attempt at cleaning. It appears that Harman-Kardon applied a water-based paint or decals on the back of the glass. Of course I started cleaning the glass only to find all the lettering coming off the glass. I had the lettering silk screened back onto the glass. I have to admit, they did a marvelous job restoring the lettering. You can’t tell it’s been re-done.
The electronic restoration consisted of:
- Completely re-tubed the receiver. The original 7408 output tubes (Industrial Version of the 6V6) tested weak so I purchased a matched set of new JJ Tesla 6V6 tubes.
- Replaced rectifier diodes with newer types.
- Installed polarized power cord.
- Installed inrush current limiter. This gradually brings up the filament voltage to the vacuum tubes, extending their life.
- All paper caps replaced. The caps installed in the 1960s were not really that bad, but the older capacitors tend to leak after time, and I was looking to get this receiver in top shape.
- Replaced all the electrolytic capacitors. The older can type electrolytic capacitors are prone to catastrophic failure and I did not want to risk smoke and melt down on this vintage receiver.
Now that it is restored it sounds just fantastic. In the last picture you’ll see this receiver in a stereo system that includes a Philips Streamium media player. I can play Internet Radio, my CD collection, and Rhapsody music through this wonderful tube receiver. This is the best of new and old technology. CD quality music playing through a vintage tube receiver – the sound is fantastic.
Specifications (from Manual):
- Circuit – Two heavy duty 7408 output tubes per channel operated in class AB1, pentode connected and self-biased. DC on preamplifier and voltage amplifier filaments.
- Music Power Output – 15 watts per channel.
- Continuous Power Output – 12 watts per channel at less than 1% distortion – 5 watts at less than ½% distortion.
- Frequency Response – +/- 1db 15-70kHz at normal listening level in the flat position (treble and bass controls at center position).
- Tone Controls – Ganged bass and treble for each channel. 10db boost and cut at 10kHz. 12db boost and cut at 50Hz.
- Phono Lo: 2.0 milli-volt
- Tape Lo: 3.0 milli-volt
- Phono Hi: 125 milli-volt
- Aux: 125 milli-volt
Update: There developed a crackling in one of the speakers and I ended up having to have the audio output transformers rewound. Apparently the insulation on the wires broke down.