Introduction: Bluetooth Tube Radio Receiver No.6 "Completely Portable
The sixth project is The Portable Tube Radio.
I once made some battery operated portable amplifiers. But they anyway needs wires to connect sources and speakers, because there was no such way to connect source without wire then. But now we've got Bluetooth, I have realized my long-cherished dream.
Step 1: The Receiver
RCA Victor 45B is a portable radio receiver.
Before the birth of transistr radio, there were many kind of such battery tub radio.
Battery tube needs 2 Power supply, "A" is for fillament, low (1.5 or 3V) voltae high current and "B" is for tube's anode,High vlotage(45 or 67.5V) low current. Around that time all of portable radios have two batteries in them.
Step 2: Tubes
3B4 is a filament type transmitting tube for battery operated portable devices.
3A5 is a twin triode for high frequency
5676 is subminiatut battery tube for high frequency
These battery tubes are filament cathode type, so Every filament circuit should be isolated.
Step 3: The Circuit
All parts and modules are crammed into such a small space, there is no way but compact and low efficient speakers, So such receiver inevitably needs more power, and output of battery tubes are very small ,so we should employ most powerful circuit without sacrificing audio quality. It is my best answer.
Parallel push pull with triode connection.
Step 4: Ingredients
1.Tube Portable receiver RCA Model 45B2
i) 3B4 (miniature battery tube for transmitter) * 4
ii) 3A5 (miniature battery tube :twin triode) *1
iii) 5676 (subminiature battery tube;triode) *1
3.Lithium ion Battery 12V
Nowadays there are small,high efficient and cheap isolatd DC-DC convers. so we can build battery tube device with single battery
4. Isolated DC-DC converters
5..PIC microprocessor 12F675 and a rotary encoder
6.Bluetooth audio module KRC-86B
7.output transformer (Ichikawa
8.12V 2.5cm fan *2
9.capacitors, resisters, universal PCB, etc...
Step 5: Disassembling
Remove Crome plated front panel and disassemble. some parts (sockets, VR, etc.) are re-used. The original receiver's main switch is connected close-and-open action of lid. I preserved this interesting mechanism.
Step 6: Build Amplifier Circuits
Cram amplifier circuit in the vacant space. The first and second stage needs one tube each, and output stage needs four tubes, so we need the place to set 6 tubes , but The sub-chassis for tubes has only four sockets and can be placed another. There is no other place to place one more tube. in such act of desperation, I employed subminiature tube 5676.
Step 7: Controller
KRC-86B Bluetooth module has play/stop FF/REW key function. I assigned these functions to tuning dial with using rotary encoder and PIC 12F675 microprocessor as below.
on/off : push tuning dial ( toggle)
FF/REW : turn clockwise/counterclockwise
Step 8: Heat Exhaust System
Originally the receiver has four tubes, and these tubes and battery are neighboring each other. Now, all of four tubes has become power tube, and manganate battery replaced lithium battery.
Unless lithium battery prohibit heat, it would explode! ,So heat exhausting system is absolutely needed.
Make windows and set fan and partition.