There’s nothing like listening to swinging jazz bands when you are out with your gal on a Saturday night. Unfortunately these days the big bands are not playing on the AM radio. It was for this reason that I had to modify my beautiful 1946 Olympic 6-606 to play music from an ipod.
Built 1946
AM broadcast band only
Battery operation off of two type B 45 V batteries (for plate voltage) and two type A 4.5 V batteries (for filaments)
Line voltage operation using special power cord with a built-in 540 ohm resistor and half-wave rectifier tube combination.
Class A audio output power amplifier without negative feedback
Second step was to hack the 6-606 so that an ipod could be played through its tube circuitry.
Summary of the restoration (see notes and photos):
The Olympic 6-606 is a portable battery operated and AC operated tube radio. Built in 1946, this radio requires special high voltage batteries to provide sufficient plate voltage for the tubes.
The tubes are 1 series tubes specifically designed to operate with a lower filament voltage and current, therefore, they utilize a cathode filament rather than a conventional cathode plate. These tubes function on primary emission from the cathode filament. This results in a tedious restoration process, where, voltages at the filaments are critical to setting the bias points of the tubes. Much effort was spent on this issue during restoration.
All paper and electrolytic capacitors were replaced
The speaker was bad and had to be replaced because the speaker windings were rubbing up against the magnet, causing a raspy/scratchy sound.
Power supply resistors had to be adjusted to re-bias the tubes for use with modern (higher) line voltage. The radio was designed for 117 VAC but in my current location I receive about 126 volts at the wall outlet. This changed the bias points of the tubes outside of the original specification, because of this I had to change the power supply circuit.
Many resistors had to be replaced in an effort to maintain original tube bias specifications.
The power cord was replaced because it was dried up and shorting out. The power cord was unusual; it incorporated a 540 ohm resistor wire (in addition to two other wires for hot and neutral from the line) that was used to power the filament of the 35 series rectifier tube. This 540 ohm resistor had to dissipate 12 watts of heat. I did not want to dissipate that much additional heat inside of this radio so I replaced the old rectifier tube with a diode, eliminating the need for the 540 ohm resistor.
Summary of hacking the 6-606
Caution: Do not attempt this hack. This is for reference only. Tube radios are dangerous. High voltage is everywhere throughout the circuitry. This radio in particular is a hot chassis radio which means its metal chassis is tied to the hot side of the input line voltage. If you make a mistake it could kill you.
The Olympic 6-606 is a hot-chassis tube radio, where, the power cord is not polarized and one terminal of the power cord is connected directly to the metal chassis of the radio. The chassis is insulated from the user by use of plastic knobs and a wooden case.
Hacking the 6-606 to play music from an ipod required the use of an audio isolation transformer so that line voltage would not be fed back down into the ipod, which could shock the user of the ipod with line voltage.
A mode selector switch was added to the rear-panel of the radio (insulating the toggle with a rubber toggle switch covering) so that either AM radio or Ipod mode could be selected.
When in Ipod mode, this switch disconnects the IF output from the envelope detector and re-routs the AF input from the volume potentiometer to the audio isolation transformer’s secondary winding.
A 1K resistor terminates the secondary winding on the audio isolation transformer, providing more of a flat frequency response curve.
Input to the audio isolation transformer is fed by two 100 ohm resistors from the Ipod’s right and left channel outputs.
Old jazz music and other old music sounds great playing out of this classic radio through the original tube circuitry.
Battery operation allows this radio to be used anywhere; on the beech, at retro photo shoots, while swing dancing.
The concept: bring vintage tube sound anywhere you go!
Engineering Notes
Olympic Model 6-606 modificaiton notes
Message feed on antiqueradios.com
Message feed on Make Magazine blog
Press & Blogs
Make Magazine Blog, “Lindy bomb in style with restored radio.
A and B battery replacement
