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