Cotton/Samson
The Cotton superhet was designed by Richard W. “Dick” Cotton in the fall of 1924. This superhet used parts from a Samson kit. My example has a nice engraved panel and the builder followed the construction article very accurately. Its very likely that my set was manufactured by a professional builder. Here are a few particulars of my set:
1. The radio operates on the standard 1920s superhet circuit
2. Front panel measures 28” long by 7” high by 3/16” thick
3. Engraved front panel
4. Samson kit consisting of the oscillator coupler, HW-R1 IF transformers, and HW-R2 audio transformers
5. National Type DX tuning capacitors
6. Federal rheostats
7. Benjamin tube sockets
8. Looks like set is wired with gold plated square bus bar
.
Samson advertisement from the January, 1925, Popular Radio magazine.
Note that transformer #4 has a narrower bandwidth and a higher relative gain than the other transformer stages. This is because the grid bias for the tube on the secondary of the transformer is controlled by the grid leak resistor and capacitor, rather than the potentiometer that controls the grid bias for the other transformers (the potentiometer control is always set at A- when I test the transformers). The secondary of the fourth transformer develops a higher negative bias on the grid of the tube, which lightens the load on the secondary of the transformer and results in a narrower bandwidth and higher relative gain. If it’s not too difficult I will often rewire the second detector so that the secondary of the last transformer is biased the same as the other transformers. That way I can get a better idea of how well the transformers are matched.
|
Type |
Peak Freq. |
Lower 3 dB |
Upper 3 dB |
Bandwidth |
Relative gain |
Pri. ohms |
Sec. ohms |
|
HW-R1, #1 |
47.5 KC |
42.0 KC |
56.8 KC |
14.8 KC |
23.6 |
69.9 |
294.5 |
|
HW-R1, #2 |
50.3 KC |
39.0 KC |
66.3 KC |
27.3 KC |
16.8 |
85.9 |
334 |
|
HW-R1, #3 |
51.3 KC |
39.5 KC |
69.3 KC |
30.1 KC |
16.8 |
89.5 |
332 |
|
HW-R1, #4 |
51.1 KC |
44.5 KC |
57.9 KC |
13.4 KC |
26 |
93.6 |
334 |
Above is a schematic diagram of the Cotton superheterodyne, as copied from an old copy of the 1926 Radio News Superheterodyne Book. The set uses a tapped loop for regenerative amplification in the first detector (controlled by a small variable capacitor from the plate of the first detector tube). The oscillator circuit has a grid leak capacitor and resistor to control the grid bias and it has a tapped plate coil; this arrangement is probably a little bit better and more stable than most mid 20s superhets.
All of the IF transformers are marked Samson HW-R1. However, there must be something different with the first transformer in the IF amplifier (the filter), because it has slightly different resistance readings from the other transformers and its primary is shunted with a .001 mfd capacitor. The transformers are supposed to peak at 60 KC, but all of mine are more like 50 KC. The fourth transformer was tested with the grid leak resistor and capacitor intact. The following table lists the electrical measurements obtained with each transformer.
National Type DX tuning capacitor.
Samson HW-R1 IF transformer.
Above is a top view of the electronic chassis. This set has not been restored and has 85 years worth of dust (just the way I like them).
Samson oscillator coupler.
Samson HW-R2 audio transformer.