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WSHU Chief Engineer Paul Litwinovich explores aspects of vintage radio, from the radio sets themselves to the people and technology that made it all possible.

A Rhode Island Radio

Paul Litwinovich

This is  a Polle Royal table radio, manufactured by the Royal Radio Corp. of Providence, Rhode Island. I estimate the date of manufacture to be between 1923 and 1925. I have been unable to locate much information about the company other than it was one of the many small manufacturing companies to come and go during the infancy of the radio industry. Many of these small independent radio manufacturers were quite successful for a few years only to fail during the great depression. Many turned out a high quality product. This particular set appears to have been targeted at the higher end of the market and was technologically advanced for its day. It consists of a 5 tube Bakelite chassis using type #01 tubes and a Bakelite front panel featuring silk screened markings with gold leaf paint. The knobs feature machine etched pointers also filled with gold leaf paint. The cabinet appears to be pine or poplar with an ebony stain. Like all radios from this time period, it is a battery powered set, but this gave it the advantage of operation in both the city and rural areas not yet electrified.  Unlike the kit radio that I featured two articles back that was designed to maximize battery life, this set was designed for maximum performance at all times and was probably sold to consumers who were not as concerned with the price of batteries. Although I have not been able to determine the original selling price of the radio, similar high end sets typically sold for a little over $200.00, the equivalent of $2600.00 in today’s dollars [1].

Credit Paul Litwinovich

Pictured with the radio is an RCA Radiola horn model 10 loudspeaker from the same time period. The earliest speakers were of the horn design. They use a coil and metal diaphragm almost identical to headphones from the same period and used the megaphone characteristics of the horn to amplify the sound. This particular speaker has a horn made out of a primitive plastic (probably a hard rubber product) and would have been considered a basic horn sold with cheaper radios. Most likely someone purchasing a radio such as the Polle Royal would have purchased a more expensive speaker featuring an ornate wooden or polished Bakelite horn. The importance of the loudspeaker was that it allowed the entire family to listen to a program rather than having to take turns with the headphones. The horn speaker would soon be replaced by the paper cone speaker which offered superior sound. By 1926, horns were on the way out.

Credit Paul Litwinovich
Inside the Polle Royal table radio

Note the colorful design of the coils, and the fact that you can see the reflection of coils and tubes in the polished Bakelite chassis. The manufacturer also concealed the wiring and minor components such as resistors beneath the chassis. This was done for good reason. This radio would have been considered a status symbol. It was probably operated with the cover open to display its “high tech” goodies and the fact that it had five expensive tubes instead of the two or three that most regenerative sets had. It was designed to look nice, inside and out. Radio was an exciting development of the times, and the manufacturer tried to convey that excitement to the user.

The coils were also a new innovation.  Now referred to as “lattice wound” but back in the day often referred to as “honey comb wound”,  this coil construction method was an improvement over traditional coils wound on a cardboard or Bakelite cylinder. They made the radio more selective. They were invented by a Rhode Island engineer named Thomas P. Giblin. Mr. Giblin also went on to start his own radio business where he produced high end receivers similar to the Polle Royal. Like the Royal Radio  Corporation, Mr. Giblin’s company did not survive the depression.

How it works: This radio uses three tuned radio frequency[2] circuits designed with independent tuning for each stage and is referred to by collectors as a "three dial TRF" for this reason. The triple stage TRF replaced the regenerative circuit and would remain the circuit of choice until the early 1930s. Later designs would gang the three stages together so that all would be simultaneously tuned by one tuning knob. If we look inside the cabinet which features a hinged top with a holding device, we see the five tubes and the three tuned stages. Each tuned stage consists of one tube with its own tuning coil and capacitor. The two remaining tubes serve as a detector[3] and an audio amplifier.

Despite the three tuning knobs, the set would have required far less skill to tune than a regenerative receiver. Each of the three knobs would be tuned to produce the loudest and clearest signal of the desired station. It would have had a more natural sound (limited mostly by the horn speaker) than the regenerative circuit as well. The set was quite sensitive and would have easily pulled in distant stations when hooked to a good antenna. It tunes the standard AM broadcast band. Selectivity (the ability to separate one station from another) was improved by the use of the new style coils, but not quite as good as a modern radio. This would not have been a problem at the time due to the limited number of stations on the air. This set is original and is still in working condition. 

Collector’s hint: These vintage battery sets make great starter sets for new collectors. Although rare models such as the Polle Royal can be a bit pricey, there are quite a few of the more common brands on the market, find them on E-bay, in antique shops, and at flea markets. They display well even if you don’t restore them to working condition. Their circuitry is simple enough that a beginner hobbyist can usually get them working without too much effort. They don't operate on the higher voltages found in the AC sets, making them safer for the less experienced technician to learn hands on troubleshooting. Other than a bad tube, not much can go wrong with them. Wire wound resistors and mica layer capacitors rarely deteriorate with age unless physically damaged. Look for sets that are complete, avoid the set with the hole in the front panel where a control used to be. Tubes for these sets can still be found but may cost as much as $30 or more each, so keep that in mind before buying a radio with empty tube sockets.

For demo and test purposes, most will run well on 45 volts, which can be obtained by connecting five 9 volt batteries together in series and using a 6 volt lantern battery for the filaments. For more frequent use, AC adapters producing these voltages are available from antique radio parts dealers such as tubesandmore.com. Although these sets work best with an outdoor long wire antenna, a modern ferrite AM stick antenna will pull in local stations.

[1] Calculated via  www. measuringworth.com website

[2] A circuit that amplifies a single radio signal to which it has been tuned.

[3] A circuit that extracts the audio signal from the high frequency radio signal

Paul was a design engineer and engineering manager in the broadcast industry for14 years before coming to WSHU in 1990. He holds an FCC commercial radio license, and an extra class Amateur radio license.
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