DXing the Crosley 51

The Crosley 51 appears to have been manufactured from early 1924 through early 1926. Many different versions were made from an early one with a tap switch on the top of the panel to the later production where it was moved to the bottom. A portable and fancy slope front cabinets were among the other variations. Single tube 51A matching amplifiers were also made and one was tried with my set.

Advertising for this radio was plentiful and ranged from the subdued claim "Will bring in local stations on the loud speaker at all times and distant stations under favorable conditions" to the more extravagant claim of loud speaker reception "up to 1500 miles under average conditions. Much greater range with headphones". The combination of aggressive advertising and low price evidently worked. It's likely more Crosley 51s were sold than any other small radio of the early twenties.

Crosley describes the circuit of the 51 as "a single circuit tuner, with controls for a vacuum tube detector, which has a tickler in the plate circuit. This tickler makes the set regenerative." This circuit is different from many competitors single circuit regenerative receivers. It uses a book condenser for tuning, and an arrangement of two spiderweb coils which control regeneration and assist in tuning. The tapped coil serves as a combination antenna and grid coil. As a consequence the receiver slightly changes wavelength coverage on antennas of different lengths. The other coil serves as the tickler and is mounted on a slider to control regeneration. Crosley used this same tuning arrangement in all of their regenerative receivers without RF amplification. All that changed was the model numbers and sometimes the audio amplifier section. The 51 also has a "one-stage audio frequency amplifier with transformer coupling". Transformer coupled audio was a standard arrangement and it was used by most early radio manufactures. However, Crosley used a high ration 9 to 1 transformer, when most other companies used 3.5 to 1. This gave high gain but caused considerable distortion.

Crosley instructions showed three ways to connect the 51. A universal rheostat was used and the differences were due to the type of tubes being used. Connections for UV-99s and WD-12s used a plate voltage of 22 volts for the detector and 45 volts for the amplifier. A C battery was recommended. The 01A connections showed plate voltages of 45 and 90 volts respectively, with no C battery. Caution: there is an internal connection from C- to A- which must be broken to use a C battery. I tried the 51 all three ways and also tried a C battery with the 01As. As expected the performance was best with the 01As and this is the way the set was tested.

Crosley's tuning instructions are very simple. Place the tap switch on the center tap and adjust the rheostat to hear a hissing noise. Pull the Varind Knob (regeneration control) about three-quarters of an inch from the panel. Turn the condenser dial and listen for a whistling or squealing sound. Adjust the Varind Knob to clear the squeal up and again adjust the condenser and rheostat controls. Although the above directions are condensed from the original, nowhere does Crosley admit that tuning in this manner would have interfered with your neighbor's radios. However, you are told it is "very desirable" to learn to tune the radio just below the squealing point.

There are some problems involved in using the Crosley 51, but when the cost is taken into account the performance is very good. The $18.50 that purchased this two tube radio would not have bought a crystal set from many other manufactures. Local stations gave good volume on the loudspeaker and the addition of the matching amplifier helped considerably in hearing more distant stations. Unfortunately the distortion caused by Crosleys 9:1 audios was disturbing and the addition of a C battery gave only a slight improvement. The 51 was one of the more sensitive radios I have used, but was not selective enough for today's crowded airwaves. In the twenties this probably did not cause much of a problem. During the daylight hours a local station, WBRW, almost completely stopped all other reception. If you tuned too close to the oscillation point just moving your hand could start the set squealing. The 51 had a very wide tuning range and on my antenna could tune up into the short-wave bands. Many times in the past I have received good short-wave reception on the 51, but during the time period the radio was tested for this article only hams and carrier waves could be heard.

A beginning radio fan with limited funds would have been happy with the Crosley 51. In view of the distortion and other problems it is surprising so many were sold. People with money could have bought much better radio in 1924, never mind 1925 or 1926.

Jim McKinnon