Ultradyne Model L-2/Phenix

Phenix Ultradyne L2 Front View

     The Phenix Ultradyne Model L-2 is another Robert E. Lacault design that came out in November, 1924. The Model L-2 is different than the Model L-1 mainly in the fact that the Model L-2 incorporates regenerative amplification in the first detector. The regeneration is adjustable by a variocoupler that is mounted on the left side of the front panel. Another feature of the Model L-2 is the use of “amperite” current regulating resistors for all eight vacuum tubes (no rheostats are required). My Phenix Ultradyne Model L-2 is wired very neatly and it was surely manufactured by a professional builder. Here are a few particulars of the set:


Columbia Ultradyne L-1<     HOME     >Late 20s Superhet

     Phenix advertisement for the Ultradyne Model L-2, from the April, 1925, Popular Radio magazine.

Phenix ad PR April 1925


Peak Freq.

Lower 3 dB

Upper 3 dB


Relative gain

Pri. ohms

Sec. ohms

#1, Type A

111.2 KC

108.2 KC

114.6 KC

6.4 KC




#2, Type B

119.0 KC

115.8 KC

122.3 KC

6.5 KC




#3, Type B

123.8 KC

120.4 KC

127.1 KC

6.7 KC




#4, Type B

118.2 KC

110.6 KC

126.3 KC

15.7 KC




     The first IF transformer is an Ultraformer Type A (with a tuning capacitor on the primary and secondary) and the remaining IF transformers are Ultraformers Type B (with a tuning capacitor on the secondary winding only). They are all air-core transformers with a specified peak frequency of 115 KC. The Type B Ultraformers were in the ballpark, but the Type A Ultraformer (the input filter) had some problems. The filter transformers usually cause all the problems. In this case the Type A Ultraformer was producing two separate peaks, the main one at 111.2 KC and a smaller one at 145 KC. Since this transformer has a capacitor across the primary and the secondary coils I suspect there is a problem with one of the capacitors (making the primary and secondary resonant frequencies different). If it was just a matter of too much coupling then the two peaks would probably have about the same intensity and be spaced at equal distances away from 115 KC. The problem could be a combination of things.
     The transformers were measured in-circuit with the secondary of the first three transformers referenced to A- and the secondary of the fourth transformer referenced to A+ (with the grid leak resistor and capacitor in the circuit). I suspect there is a problem with the grid leak because the fourth stage had a relatively low gain and a wide bandwidth. The table below records the bandpass measurements.

     Schematic diagram of the Phenix Ultradyne Model L-2, from the Spring, 1925, Citizens Radio Call Book.

Ultradyne L2 Schematic CRCB Spring 1925

     Phenix tuning dial. Note the REL in the center of the dial.

Phenix Tuning Dial
Phenix Ultradyne L2 Front Panel Engraving

     Close up view of the engraved panel.

     Close up view of Phenix Type B Ultraformer.

     Thordarson audio transformers.

Phenix Ultraformer Type B
Phenix Ultradyne L2 Audio Amplifier

     Phenix oscillator coils.

     Phenix regeneration variocoupler.

Phenix Oscillator Coils
Phenix Ultradyne L2 Regeneration Coils

     Top inside view of the Ultradyne Model L-2. The expertise of the builder is evident.

Phenix Ultradyne L2 Top View