Opus 3 Japanese Plastic age Radio. This time I am going to make bedside radio for listening music at night.
This is a Japan Victor Corporation's product.It looks something different from other radios made around the same years in Japan. General Electrics USA once had had a similar designed radio in the products lineup (I have once restored it) . So the exterior design of this radio must be a copy of it. It might represent Japanese people's yearning for USA.
Step 1: A Lump of Tar Arrived
I found it at Japanese auction site. When arriving, it was terribly ruined. Suspicious tarry substance was heavily sticked on all over the surface,and the inside was full of dust, backboard had been dissapeared.
But such condition might be acceptable because it costs only 1000JPY (US$10). And from my experience, the thicker the tar on surface, the better conditions are maintained because the tar would perform as a protector from light and oxygen, I think.
Step 2: Wash It, Wash It and Wash It Down.
At first, strip off all the components, and remove all the parts on chassis except sockets. and wash them down.
Step 3: The Circuit
The new schematics is shown below.
This something queer circuit is called "Super Triode Connection (Version 1)" invented in 1986 by Kamijo.
For details, please visit the following website:
Originally, this radio is a transformerless 5 tube superhet. I have been avoiding to build transformerless devices for averting risk of electric shock, because I am a bit of a scatterbrain. So this time I add power transformer too.
Step 4: Select the Speaker
The original speaker is 5inch very normal narrow range for AM receivers. So I replaced it.
The new speaker is SICA Z002320, coaxial 2way. It is very sensitive for a modernistic speaker.
Step 5: Modify Chassis
SICA Z002320 is almost as same diameter as original speaker but somewhat thick. so it needs modification of chassis.
With an iron saw and hammer process it.
Step 6: Put Them Together
Remaining 4 of 5 tube sockets build a all 7 pin miniature tube amplifier. and put the speaker on, and install Bluetooth audio receiver.