Please scroll down for the photos
Five tube Superheterodyne Radio (actually 6 tubes if the ballast tube was included)
This radio project came out of a January 1937 Popular Mechanics magazine.
The radio had a short wave band as well as the standard AM broadcast band.
This was about the only Popular Mechanics radio circuit where they didn't
parts list or values for the components. Secondly, they specified some "stock" coils
for the oscillator and RF stages of the receiver. It said at the end of the article, send
a postcard to Popular Mechanics Magazine and they will send you a detailed blue print.
I am afraid that they wouldn't send the blue print 67 years later. I have no clue about
where to find the short wave/ broadcast coils, so I omitted the short wave band
on this receiver. Perhaps later I will make it go short wave if I find the combination coils.
I found that the tube line-up was standard for the late 30's for most
receivers of the
5 tube variety. The mixer/oscillator is a 6A7, IF amplifier is a 6D6, detector/first
audio is a 75, and the audio output is a 41. I found the exact component values and a
very similar wiring diagram in my 1937 Supreme Radio Circuits Book.
I used the circuit values for a FADA Model 354 radio.
The original design was for a series filament transformer less circuit,
which is a serious
shock hazard. I used a 12V center tapped filament transformer with a 115/220VAC primary.
I fed 115 volts into one winding and use the isolated 115VAC for the B+.
I used 6 volt tubes instead of the series filament types.
The power supply uses a 6X5 half wave rectifier. The 2 blue capacitors
are paralleled 860 Mfd
electrolytics which give a brute force filter instead of a filter choke/capacitor filter.
The ripple from this power supply is only about 50 millivolts RMS. The radio has no hum at all.
The alignment was a bit tricky. The 455Khz IF alignment posed no problem,
but the oscillator
tracking to make it match the dial face was a bit difficult.
The dial plate and drive is totally hand made. I scanned a dial plate
1939 Zenith portable radio. The reason that I chose that dial plate was because
of the Art Deco numbers and layout. After "fixing" all the blemishes on the dial scan
with my software program, I made a negative image for the dial plate.
The background is now white and the printing is black. I also eliminated the brand
name on the face plate. A print was made and glued to a 1/8" piece of polycarbonate.
The art deco dial pointer from the Zenith radio is used. An art deco wooden cabinet
will be built for the radio. The speaker will be mounted on the left hand side of the cabinet.
The receiver works very well and I had a chance to compare it with a
receiver which uses an equivalent tube line up. The sensitivity and selectivity are on
a par with the Hallicrafters on the Broadcast Band.
I have never built a standard broadcast type superheterodyne before and
it was a very
interesting and satisfying project. I had 80% of the parts in my parts bins.
See my second page where the radio undergoes a modification of a new dial and short wave bands.