Project 3 – Superheterodyne octal tubes

This is a work in progress. The radio will probably be completed in the first half of 2010.   

It will have 5 section; rf, lo-mixer+if, if-amp2, det+first-af and af-amp.   

   

   

January 8 2010   

Well, I had time to complete my 5 tube radio project.   

[youtube=http://www.youtube.com/watch?v=PFwE5W0Id50]   

I have opted for a 1940’s classic, an all American 5 superheterodyne AM receiver.   

I had a few 12SA7, …, 50L6 series lying around the shack and two old 455kc ‘IF’ transformer.   

The schematic is quite straight forward, the usual RF/MIXER, IF amp, DET/AF amp and power amp.   

The strength of the signal – from the detector section – is use to AGC.   

Tube heaters are connected in series and a 35Z5 is use to provide the B+ from an isolation transformer connected to 117AC.   

It was quite fun to revisit an old part of radio history.   

Oh yes, tuning was a bit tricky using a scope.  When the scope was disconnected, the circuit was detuned!  Measuring the AGC negative voltage and using my ears was much more effective.   

A frequency counter was use to calibrate the L.O.   

By the way, Max Robinson has a lot of valuable information on his site ‘FUN WITH TUBES’ about tube radios and AA5 theory at http://www.angelfire.com/electronic/funwithtubes/.   

And Dave N2DS has build very nice radios http://makearadio.com.