Repair of a 1954 Arvin metal midget tube radio model 840T скачать в хорошем качестве

Repair of a 1954 Arvin metal midget tube radio model 840T

A couple of years ago, I purchased this Arvin four tube metal cased radio for two dollars at a roadside sale. I actually know the guy who had it and it had previously been used for nothing more than decoration on a wooden shelf on their front porch (these people were real big into the "country cutsie arts & crafts" thing). I was rearranging the junk in the shop the other day, found this radio, and decided to play around with it. The first thing I did was ohm out the RF/IF coils and the audio transformer to make sure they were not open. In the past, I've seen a few of these midget tube radios with open coils/transformers and that can be a problem. After I determined that the coils and transformers were OK, I replaced the old paper and electrolytic capacitors. All the paper capacitors were leaky and the multi-section electrolytic filter capacitor was totally open. After that, I checked for continuity across the AC plug and found an open; which, indicates a burned out tube filament, open power switch, or other fault in the filament string. Originally, the 12BE6 converter tube was missing; but, it was no problem coming up with one of those from my junk. Then, I found that ALL THREE of the remaining tube filaments were open; which, is something I've never seen in the 25 years that I've done this. I figure that either lightning struck the radio or the radio was plugged into an improper power source. After I replaced the tubes, the set came to life; but, the volume would not go down. The fault turned out to be the volume control; which, was a 2 megohm unit. In my junk box, I found a physically identical control that was a 1 megohm unit; which, works OK. I replaced the power cord and installed a new antenna wire, put it all back together, and the radio was dead. After not finding an open tube filament, I pulled the chassis back out of the cabinet and found that the power switch on the rear of the "new" volume control had opened. I'm sure I have a replacement around here somewhere; but, for now, I have the power switch jumped out. Later, I want to replace the non-polarized AC cord with a polarized cord and I also want to wire the AC switch in the "hot"side of the line. With the switch in the neutral side of the line, there is always a chance of a "hot" chassis, no matter the plug position. If the chassis is cold with the set on, it will be hot with it off (due to a path through the filament string to the chassis). With the switch in the hot side of the line, this problem will be eliminated (assuming that the AC outlet is wired correctly). Another problem I need to address is the "across the AC line" capacitor. Vintage AC line capacitors are an accident waiting to happen. Modern film capacitors like what we use in the rest of the set are an improvement; but, for AC line bypass, it is best to use a special safety capacitor rated for AC line use. As long as I have the radio, I'm not worried too much about the AC cord or the line bypass cap; but, I would want to make these revisions if I were to pass this set along to someone. Being a metal cased radio, there is danger of shock and we want to keep that danger to a minimum. These radios sold for a cheap price when new and are not the best performers; but, considering that they only use four tubes, they are OK and certainly better than many modern AM radios. These radios do not have an IF amplifier stage; so, the circuit relies on whatever gain that's provided by the converter stage. Generally, these radios require a long wire antenna (an outside antenna would be best) and they do best with strong local stations (although this one was picking up several distant stations with an antenna wire running out the shop window. These small metal midget radios date back to the late '30's and lasted up until the mid '50's. Most of them used the larger octal based tubes; but, the last ones (radios such as this one) use the smaller severn pin miniature tubes. There were also some two and three tube models made during the late '30's-early '40's and these are also found under the Sears Silvertone brand name.