Building a Subminiature Radio.
 

Hello, I am a new member of this forum. My real name is César and I'm also amateur radio in Spain as EA1AUI, ...and this is my first post so please excuse me...

I had been thinking for a long time about the construction a superheterodyne tube receiver as small as possible in size, for medium and short wave ranges, and pluggable to 220 v AC.

So after digging through various drawers and boxes, I managed to gather several sub-miniature tubes with their corresponding sockets (from the scrapping of an old radio beacon from the 1960s), as well as a small tandem, two FI, also from a Philips scrapping. and a set of tuning and oscillator coils, mounted on switch.

I then proceeded to design the corresponding schematic diagram, finding the greatest difficulty in the converting step because there were not any hexode or heptode valve, the available tubes were only triodes and pentodes, for which I was forced to “experiment” arranging a triode as local oscillator, with the output coupled through the screen grid of the RF amplifier / mixer pentode.

The detector circuit had no major problem with the incorporation of a simple germanium diode.

For the supply, starting from a waste core, I made a small transformer with a 6.3 V output for the filaments and another 100 V output, rectified by a diode bridge for continuous A.T.

https://fotos.subefotos.com/330736ac...1cdf3c3f8o.jpg


The rest of the circuit does not deserve further comment since it conforms to classic patterns, only pointing out the need to have had to calculate and build another transformer for coupling the speaker.


https://fotos.subefotos.com/b1ae33e9...e12a8efdco.gif
https://fotos.subefotos.com/09ae157f...acd46ffc3o.jpg
https://fotos.subefotos.com/6a2ba1f8...c4d4b583fo.jpg

With a piece of aluminum sheet I machined the chassis and once the measurements of the whole set were determined, I provided him with a box-cabinet made of wooden board.


https://fotos.subefotos.com/a1ce31f2...fead9e927o.jpg
https://fotos.subefotos.com/d9b6e730...cd93d3be1o.jpg
https://fotos.subefotos.com/ef6a058b...91cbc2c3fo.jpg

......And once adjusted and tuned, the operation is highly satisfactory.

https://fotos.subefotos.com/25de62a7...c0639ddfeo.jpg

Re: Building a Subminiature Radio.
 

Hello César and welcome to the forum, perhaps post an introduction about yourself in the Member Introductions section.

Well done on the miniature valve radio, what you have done, is on my list of projects for some time in the future. I will also be using miniature valves (wired) as i have several of them both triode and pentode. To me you have done a wonderful job and I hope you are proud of it.

Again I say welcome aboard and hope to see many more of your projects.

Adrian

Re: Building a Subminiature Radio.
 

Excellent work!

Re: Building a Subminiature Radio.
 

Good work, a superhet is something I always wanted to build.

Re: Building a Subminiature Radio.
 

Many thanks AdrianH, Colin Ames and retailer for your kind comments.

Re: Building a Subminiature Radio.
 

Lovely project. Welcome and well done.

Aub

Re: Building a Subminiature Radio.
 

Thank you Aub
Regards
César

Re: Building a Subminiature Radio.
 

Nice one! that's the sort of thing I like to do , well done. Mick.

Re: Building a Subminiature Radio.
 

Well done César and welcome to the forum. You’ll fit in well here.
I’ve always wanted to build a battery valve set as small as possible using the USSR pencil ones.... one day!

Peter

Re: Building a Subminiature Radio.
 

Hi Mick and Peter. Many thanks for your nice words.
I hope you decide some day make another miniature radio. .."If you want, you can"..
Thanks again and best regards.
César