Mate for the Mighty Midget 3 Tube Superhetrodyne Novice Receiver Project from the Beginner and Novice column in QST April 1966

I remember the moment very clearly.  June 1966 I was sitting in a lawn chair reading a stack of QST's that I had brought along to the summer cabin.  The February 1966 issue the Beginner and Novice section introduced the "Mighty Midget Transmitter", a 10 watt crystal controlled transmitter.  The April 1966 issue Beginner and Novice section introduced the "Mate for the Mighty Midget" which was a three tube superhetrodyne Novice type receiver.  Over the course of that summer I read and re-read those articles a jillion times.  Being 13 years old, I didn't have the electrical or mechanical skills to pull off such a project so I could only dream about it.  In 1970 I bought a handful of the parts.  In 1976 I bought more parts.  In 2021 I decided to build it while I still had the ability to do it.  This project is only my second homebrew radio project so I am still learning things every second of the way.

The photo below shows the schematic diagram.  It is a 'traditional' superhetrodyne receiver with an RF front end, an HF oscillator, the Mixer, a dual crystal filter, one Intermediate Frequency (I.F.) amplifier stage, a 455 Kc IF transformer, diode detection, and one stage of audio amplification.   Most "Beginner" receivers don't have an RF amplifier front end and the antenna goes directly to the mixer so I was pleased to see this one had that amplification stage.  It also uses two military surplus crystals to create a crystal filter for the 455 Kc IF.  Yes I know KiloHertz is the unit of frequency today but for us 1966 guys it's "Kilocycles".  

STATUS:
February 27, 2021. The wiring is finish and I am the debugging mode now.  So far I've found just a missing wire and one mis-wired connection.  I have the RF amplifier working.  I do notice a slight resonance difference between L2/C1A-B and L4/C1C-D.  I am ignoring it for now but it's likely due to either an extra or a missing turn on the coil.  C1 B and D did not resolve it fully.  The HF oscillator is working on 40 meters although it's a tad high in frequency, sitting at 7475 instead of 7455 so I will be tweaking that.  The mixer is working.  The crystal filter appears to be working but the IF from the mixer is currently 475 Kc instead of 455 Kc, so signals are very attenuated.  The IF amp, detector, and audio amplifier is working.  I heard the signal generator in the Trimm crystal headphones this morning.  I couldn't hear any signals yet.   So the project is coming along nicely, close to finishing, but still a few issues to resolve.

March 26, 2021.  Great news, the MMMRX is functional on 40 meters!  I think blown 45 year old Geranium diodes in the audio detector were the final culprit.
  I hooked it up the antenna and heard plenty of 40m cw and some SSB signals.  Tuning is sharp without a vernier so today I attached the front panel with the National vernier.  I will fire it up this weekend and see how it's working.  While I haven't checked out 80 meters at all, I did bandswitch to 80 and was greeted with WWV.  I don't know if it's 2.5 MHz or 5 MHz, and it was nice hearing that, but the receiver isn't designed to go there so I have a problem yet with 80m. 



Because of the wonderful nostalgia from 1966 I wanted to duplicate the article as closely as possible.  The photo below shows the front panel and cabinet of the radio sitting above the receiver as shown in the 1969 ARRL Handbook.  Mine uses the same National vernier dial, same cabinet, and similar knobs.  I am pleased with the front panel look.  I will add white control lettering later when the project is done.


Here is the front cover of the April 1966 QST issue.  The cover is starting to fall off but it's in good shape after 55 years.


Here is an early photo of the chassis top facing the front.  When it's complete I will mount the chassis to the cabinet front panel.   Note the crystals were put in just for the photo.  They are not the final crystals.



Here is a photo of the chassis from the rear.  Note the similarity to the original.   With one exception of the power transformer, the rest of the layout is very similar.  I decided to leave the power transformer off the chassis due to weight, size, and potential of audio hum.
Everything is so crammed in there that I'm already worried about hetrodynes and oscillators coupling into everything.  I think the layout violates several 'good practices' such as keeping the HF oscillator and BFO shielded and separated from each other. 



Here is a photo of the chassis bottom.  It is a lot tighter fit than I like.  My next receiver project will be spread out more so it doesn't take so much time trying to
figure out where to cram some part in.

February 27, 2021. The wiring is finish and I am the debugging mode now.  So far I've found just a missing wire and one mis-wired connection.  I have the RF amplifier working.  I do notice a slight resonance difference between L2/C1A-B and L4/C1C-D.  I am ignoring it for now but it's likely due to either an extra or a missing turn on the coil.  C1 B and D did not resolve it fully.  The HF oscillator is working on 40 meters although it's a tad high in frequency, sitting at 7475 instead of 7455 so I will be tweaking that.  The mixer is working.  The crystal filter appears to be working but the IF from the mixer is currently 475 Kc instead of 455 Kc, so signals are very attenuated.  The IF amp, detector, and audio amplifier is working.  I heard the signal generator in the Trimm crystal headphones this morning.  I couldn't hear any signals yet.   So the project is coming along nicely, close to finishing, but still a few issues to resolve. 

March 26, 2021.  This week I took the MMMRX out for a spin on 40 meters and heard a lot of CW and a few SSB signals.  To aid in debugging I removed the two crystal filter and replaced it with a 455 KC IF transformer.  Today I attached the front panel in order to use the vernier dial as the tuning is too sharp without the vernier.  I also removed the 455 KC IF filter and put the crystals back in.  I heard signals from the signal generator so I'll take it out on 40m tonight for a spin what I hear.  While I haven't checked out 80 meters at all, I did change bands and was greeted with WWV on either 2.5 or 5 MHz.  Obviously the Local Oscillator is way off.   I've included a couple more photos.

Photo below is from March 26, 2021 and is the final configuration.

Photo below is from March 26, 2021 and is the final configuration.

I recently bought a Rigol DS815-TG spectrum analyzer and it is a real joy (!) viewing signals in the frequency domain besides the time domain.  Mixer outputs are a hot mess on an oscilloscope but signals are crystal clear on the spectrum analyzer. 

While I am not expecting to much in performance, the 13 year old in me is ever hopeful that this 1966 Novice receiver will be the most wonderful radio ever made.   73, Scott WA9WFA