Project 4 – SW tube receiver

Update – 22.05.2010   

I did a little work on the project:   

Replaced 10.7 “IF” cans by 455kc ones.   

Selected all 12 volt filament tubes: 12BE6 (converter), 12BA6 (IF), 12AV6 (DET, AVC, AF-PRE) and 12BA6 (AF-AMP).   

Fixed B+ at 20 volt (-12 + 12 from an ATX-Power supply).  Current is around 4ma (yep!). 

Heaters current = 650ma. 

I am starting to get results from it!   

   

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Schematic – version 1

   

Next steps:   

– add  rf amp stage
– add a third “IF” stage (done)
– add a magic eye tube on the AVC signal (done – but wont make it to the final version)
– add a regeneration stage on V2 (not shure any more …)

Update – 28.05.2010

With the initial concept, I was thinking of a 50C5 35W4 12BE6 12AU6 12AV6 alignment with 10.7 IF.

Finally, I decided that it was too usual and I did not want it to be 117volts live.

So, the actual state of the project is:

Tubes: 12BE6 (converter), 12BA6 (IF1), 12BA6 (IF2), 12AV6 (DET) and 12BY7 (AF-AMP – It as a better sound than a 12BA6),

2 x IF stages,

3 x 455kc transformers used in transistor radios,

Controlled auto-Oscillation of the first IF-AMP (BFO) for SSB and CW reception,

Interchangeable L1, L2 and L3 for multiband,

Very low (24volts – from an ATX power supply: +12 + -12) B+. I did some tests with 12volts and it works very well with headphones.

I will add a frequency counter on the converter tube (LO – IF) to display the reception frequency using a 74HC161 and an Arduino board to drive Nixie tubes or a LCD display.

Looking at the following picture, I understand why I love those tube radio projects; they are so great in the dark…

 Nixie or LCD ? …

Schematic – version 2

 

Update 20.06.2010

I’ve made some progress on my 5 tubes shortwave radio.

The frequency counter prototype is working.

I’m using a MPF102 as an RF amp, then the signal is feed in a 74HC161 (16x prescaler) and finally into an atmega328p for counting.

See the frequency counter at work:

=====================
Source code:
=====================

/*
 Project:   Frequency counter for the 5 tubes (3 IF) homemade shortwave receiver
 By:        VE2CUY – Alain Boudreault
 Date:      June 2010
*/

#include <FreqCounter.h>
#include <LiquidCrystal.h>
#include <stdio.h>
#include <string.h>

//#define __debug

 // initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 3, 2, 1, 0); 

// Read fz input via Atmega328 pin 11 (arduino digital 5)
void setup() {
  lcd.begin(16, 2);
  lcd.print(« L.O. frequency »);
 
  #ifdef __debug
    Serial.begin(57600);                    // connect to the serial port
    Serial.println(« Test fz counter »);
  #endif
  lcd.clear();
  delay(500);
}

long int frq;

void aff_number(long int number){
    long int divider = 100000;
    long int reminder;
    int digit;
   
    for (int i=0;i<6;i++){
      reminder = number % divider;
      digit = (number – reminder) / divider;
 
      #ifdef __debug
        Serial.print(digit);
      #endif
      lcd.print(digit, DEC);
      if ( i == 1 || i == 4) {    // format -> 00.000.0
        #ifdef __debug
          Serial.print(« . »);
        #endif
        lcd.print(« . »);
      }
     
      number=reminder;
      divider/=10;
    } // for i
   
    #ifdef __debug
      Serial.println( » MHz »);
    #endif
    lcd.print( » MHz « );
   
} // void aff_number
void loop() {
  FreqCounter::f_comp=1;
  FreqCounter::start(10);

    while (FreqCounter::f_ready == 0){
      frq=FreqCounter::f_freq;
    }
    
    lcd.setCursor(0, 0);
    lcd.print(« LO: »);
    frq*=16;                  // Adjust for prescaler
    frq+=90;                //frequency fine tuning
    aff_number(frq);
    lcd.setCursor(0, 1);
    lcd.print(« FZ: »);
    aff_number(frq-4550);  //IF = 455KC
 }