E.I.S./Leutz Model L/C Hybrid
The radio described in this section is based somewhat on the Experimenters Information Service (E.I.S., or Leutz) Model L and Model C superheterodynes. The original builder cut out most of the front end tuning controls from the Model L and ended up with this set. A true Model L has two separate 40-inch long cabinets and six main tuning controls. E.I.S never put out plans for a radio exactly like this one. Here are a few particulars of this set:
1. The set operates on the standard 1920s superheterodyne circuit.
2. The front panel measures 36” long by 8” high by 3/16” thick.
3. E.I.S. Model L filter transformer.
4. Five RCA UV-1716 IF transformers.
5. E.I.S. style four-inch main tuning knobs.
6. General Radio rheostats and tube sockets.
7. Four Weston panel meters.
8. Ten tubes.
9. RCA UV-712 audio transformers.
10. The manufacturer of the oscillator and antenna couplers is unknown.
The above photo is a top inside view of the set. There’s a lot of stuff packed in the 36” long cabinet. I don’t like the bright orange antenna coupler, or much of the sloppy wiring inside this set. I’m tempted to change things. On the other hand, I’m kind of a purist too, and something inside me tells me to leave it just the way it is. This is the way the original builder made it and I should probably accept it for what it is. That being said, how important is this set anyway? I may just change a few things!
Inside angle view of the interior.
Close up of the two RCA audio transformers.
Close up of the E.I.S Model L filter transformer.
Close up of the E.I.S. style 4-inch main tuning knobs.
Close up of two of the RCA UV-1716 long wave (IF) transformers. Most of the parts date the set to the 1922-1923 time frame. The RCA UV-1716 long wave transformers were introduced in 1922 and RCA recalled most of them in early 1924 to make it more difficult for people to build the Leutz superhets.
The table below records the bandpass data and resistance measurements of the IF transformers. I was impressed with the Model L filter transformer because the primary and secondary coils were each shunted with a fixed capacitor yet the transformer produced a single peak very close to 30 KC. Most of the RCA UV-1716 IF transformers peaked very close to 30 KC also. The UV-1716 transformers have a high relative gain and five stages of IF amplification was more than adequate; three stages would have been sufficient. The last transformer (driving the second detector) was rewired so that its secondary winding was referenced to A- instead of A+ and no grid leak resistor or capacitor was used.
|
Type |
Peak Freq. |
Lower 3 dB |
Upper 3 dB |
Bandwidth |
Relative gain |
Pri. ohms |
Sec. ohms |
|
#1, E.I.S. Model L filter |
29.4 KC |
26.0 KC |
32.9 KC |
6.9 KC |
11.0 |
65.7 |
64.8 |
|
#2, UV-1716 |
30.0 KC |
16.3 KC |
57.0 KC |
40.7 KC |
14.4 |
144.2 |
409 |
|
#3, UV-1716 |
30.0 KC |
16.6 KC |
59.9 KC |
43.3 KC |
14.4 |
151.0 |
391 |
|
#4, UV-1716 |
30.7 KC |
18.2 KC |
55.4 KC |
37.2 KC |
14.2 |
137.4 |
387 |
|
#5, UV-1716 |
30.0 KC |
16.5 KC |
59.4 KC |
42.9 KC |
14.8 |
138.9 |
416 |
|
#6, UV-1716 |
38.9 KC |
26.3 KC |
55.4 KC |
29.1 KC |
16.2 |
144.5 |
401 |
Advertisement for the RCA UV-1714 and UV-1716 radio frequency transformers, as copied from the January, 1922 Radio News magazine. These transformers were some of the first commercial radio frequency transformers available. Radio Frequency amplification was becoming very popular about this time and several different companies started to fabricate effective transformers.
.