Arvin Radios.
Arvin Radios ~ Bill Jones
While there is no shortage of Arvin’s, a particular model may, at times, be difficult to find. I have been looking for an Arvin 422 for some time and finally found a cream colored one. I did not care if it was brown or cream since I plan to restore one of each. The brown is the 422 and the cream (Ivory?) is the 422A. The electronics are much the same for all of the four tube Arvin’s, but there are minor changes. The 422 that I just restored had the I.F. transformer on the underside of the chassis and the transformer was not shielded. Most four tube Arvin’s that I have seen have had the I.F. on the upper chassis with shield. In restoring the chassis of this Arvin I found an oscillation at the low end of the dial. I have noted this type of oscillation before with other radios. I paid little attention since it is removed by a slight detuning of the I.F. While checking this Arvin I began to wonder why this was happening. The oscillation was of a type that is often called motor-boating. After some investigation it was found that the I.F. transformer leads were radiating to the antenna input. That is, it was being picked up by the antenna lead – from the I.F. transformer. It only occurred at the low end of the band because the I.F. tuned frequency is very close to the R.F. input frequency at the low end of the dial. Again, while not serious, it is interesting.
While I did tend to blame the unshielded I.F. transformer for this oscillation I have noted it before on sets that had shielded transformers. It is easy to solve the problem by using a one to two foot shielded lead (shield to ground, connected at the antenna coil) and then connecting the real antenna to the center of the shielded lead. If you have ever worked on TRF radios that have a high gain you will remember the oscillation problem. In the TRF case it is a true RF oscillation and you will hear a whistle from the set when tuning to a station. In many cases, shielding the antenna lead to where the real antenna connection input is a few feet from the set. This is an easy cure for the problem.
Some manufacturers were very conscientious about shielding. They used covers for the variable condenser, the tubes of course, and a cover for the bottom of the chassis. I am thinking of the TRF Majestics in particular. The shielding was done to keep radiation from the wires inside the set from getting back into the antenna. Most manufacturers had low gain sets and some did little in the way of shielding. Some did not understand the problem. The oscillation could be cured by using a low gain in the R.F. stages and high gain audio– or often by slightly detuning the RF stages. In such case, the manufacturer would usually advise the customer to use a good or long antenna. A really good antenna then allows a lower gain RF amplifier. Arvin makes such a suggestion, but perhaps not for the same reason. The Arvin actually has a good performance considering its simplicity.
The Arvin does not have a large gain in the R.F. section but it is better than you might think. The antenna coil has a gain of greater than ten. Note that it has an iron core in the antenna coil. “Iron core” was the beginning of Ferrite, while then called an iron core, it was still Ferrite. This could be considered “High Tech” at the time the Arvin was produced. The Arvin I.F. stage has a gain of better than ten, but to the primary of the transformer it will be greater than that.
One reason the Arvin has a sensitivity better than one would think is because it has a large audio gain. Note that there is no resistor in the cathode of the audio amplifier (12SQ7), thus omitting a large value audio bypass. It also has a very large resistance in the grid circuit of the audio amplifier. This large resistance then provides the grid bias for the 12SQ7 audio – it is what was once called a grid leak resistor. The “grid leak” was common in the early days of radio, and was just a simple but nice way to obtain grid bias – unfortunately the tubes of that day caused the bias means to be relatively unreliable. Also note that the Volume control is two meg-ohms. In most sets this control resistance is usually in the K-ohms range in order to reduce hum difficulties. The plate resistor of the 12SQ7 is also quite large – all these together give an excellent audio gain but also provide a high Q for the I.F. transformer secondary since it is so lightly loaded. This then improves the selectivity. One interesting note - the tuning condenser has the oscillator plates of the shaped type with a variable trimmer only on the oscillator section - the R.F. variable condenser has no trimmer. The circuit then saves a padder and a trimmer. The padder condenser is necessary when the plates are not shaped. The padder is in series with the oscillator variable when the plates of the variable condenser plates are not shaped. The padder condenser circuit contributes to a slightly lower R.F. gain even if correctly aligned as compared to the shaped plates. The alignment of the Arvin R.F. stage is then accomplished by varying the oscillator trimmer, while also varying the main variable to keep the station audible (at the high end of the dial} until the strength of a small R.F. signal is maximized. Cheap and well designed - or inexpensive and well designed.
The set has a reasonable performance with few components – it was cheap, but that was the idea.
I was somewhat disappointed that my set had no label. It is often difficult to remove labels before restoration. If it does have a label I will scan the label before stripping the paint. If it is not possible to successfully remove the label it can be restored by use of a Photo Software program. I found a picture of a 422 on E-bay and it had a picture of the label that was just readable. I was able to copy the picture and use it to make a label for my Arvin. You will find a copy of the label below. Pictures of the 422 are below. Since restoration of the 422 I found a 422A. This set has been restored and pictures of both sets are also shown.
422A (Cream)
422 (Brown)
Since restoring these sets I have become somewhat interested in some of the more early Arvin’s and now have found three that I plan to restored. They were all found at about the same time and will be restored as time permits. One of the sets is the Model 40 and is a two tube (TRF) set and considered one of the first of the metal Arvin’s. The model 40 came with two different dials, one with Mighty Mite on the dial and the other with Arvin on the dial. It came in either Cream or brown. This two tube set is said to have sold for less than five dollars. It is one of the most difficult of the Arvin sets to find. A later model is the 402, and is a three tube set and is also a TRF. It came in a brown with black specks – it will be a challenge to restore this set and get the specks the proper size, the black specks have a diameter in the order of one sixteenth inch and are randomly splattered on the metal case. I also found a model 422 which was made after the war and this set is black with a silver dial. A picture of these unrestored sets is shown below with a copy of the label plus the tube layout. The label is pasted to the bottom of the set after placing the tube layout on the label.
Questions or Comments? Please e-mail me at whnj
MODEL422 LEFT
MODEL40 CENTER
MODEL402 RIGHT
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