Bluetooth Tube Receiver Project 5 Japanese Prewar Era's 3-Tube



Introduction: Bluetooth Tube Receiver Project 5 Japanese Prewar Era's 3-Tube

This is the fifth set of my project.

I bought it on an auction site several years ago. It was solid and made with great care, and was not cheap.

The original set was a triple tube 0-V-1 receiver, 12B(rectifier)-24B(positive-feedback detector)-47B(low frequency amplifier) .

Step 1: Ingredients

1. An old 0-V1 radio (Televian M33)
2. Vacuum tubes
19 (Twin triode for output stage)*1
56 (Heater-cathode type triode)* 2
3.output transformer (Ichikawa ITPP-3W)
4.interstage transformer(Hammond 124E)
5.AC Adapter 5V, 2V
6. UZ socket *1 UY socket *2
7.full range speaker unit
9.Bluetooth audio receiver module KRC-86B
10. capacitors, resisters , wires, ...etc.

Step 2: Planning

It is originally very well-designed compact receiver, so there is not abundant space in it to rebuild amplifier.

The inner space of this set is too small to build a ordinary push pull amplifier like opus 2. However if build single-ended, it needs larger output transformer. There is no such space to put it.

One day I found a old tube named 19. It contains a pair of direct heated triode in it. if you use this tube, you can make output stage with only single tube.
Class B push pull amplifier needs fixed bias or interstate transformer, fortunately I had one made by Hammond. For push pull does not need such large output transformer as single ended.
The schematics is shown below.

This is my first class B push-pull amplifier

Step 3: Restoring Chassis

The Original power transformer were stored under the chassis. its cover is part of the back of the design,so was preserved intact. The rusty chassis was polished and repainted.

Step 4: Knobs

It remains two three original knobs which had been used as a positive die in project 2. With the female die made in the other instructables . I made the rest one knob.

Step 5: Power Supplies

The B power supply is earned with directly bridge rectifying the AC100V. The heater / filament power are supplied by the trans-typed AC adapter.

Step 6: Arrangement

The right is interstage (phase inverter ) transformer, Left is output transformer.

Step 7: FF/REW System

Originally, left knob is main switch, right knob is tuning, and center is for regeneration. (Regenerative receiver generally has no volume control).
Now the left remains original function. right becomes a volume control, but the center has no function.

I mostly use KRC-86B Bluetooth module recently. This module has fast-forward and rewind control function, so I decided to assign these functions to center knob.

The easiest way is using a rotary encoder and a microprocessor, but this time I stuck strictly to analogue solution -- a cam and micro switches.

Step 8: Finish

The classical direct heated tube amplifier is just turned off.

All currents of filaments are DC. so there's almost no hum noise

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