![]() ![]() His skills are appreciated towards the restoration and preservation of radio antiquity. Our technician is a graduate from the Missouri Institute of Technology Kansas City, MO (now DeVry University) who holds an FCC 1st Class/General Radio-Telephone License with prior technical experience in the field of broadcast and commercial communications. We take pride in our work and service every radio with tlc as though it were our own. Our shop is equipped with the necessary tools, electronic test gear, tubes, parts, manuals and schematics to do the job right. We've restored hundreds of radios locally and nationally ranging from family heirlooms and keepsakes to museums, individuals, and collectors. We repair and restore all makes and models of old tube type radios including: cathedral, tombstone, console, deco, catalin, plastic, bakelite and novelty. ![]() For over 30 years we have specialized in professional antique & vintage radio repair service and will electronically restore your old radio back to it's original factory specifications. Usually these resistors are low in value at around 2.2 Ω, so I replaced it with a higher wattage 2.Classic Radio Restorations located in St. It should have been a one-watt type, but instead they used a ¼-watt type, which is probably why it failed. A meter test indicated that the resistor was close to going open. Whilst looking at this resistor closely to determine its value, I noticed a dark mark on the body indicating damage caused by overheating. In this circuit, the emitters receive current through a common resistor. Usually the drive is close to supply rail, and therefore I would have expected approximately 7 V at the emitter, however it was only 3 V. In this type of configuration, the emitters of both transistors usually join to a common voltage rail, whilst the collectors drive the primary winding of a transformer to recombine the opposing phases of audio. Either both were faulty, or both were working below established parameters. I decided to check the voltages at their terminals and both transistors had identical values. The power output stage is a Class B Push-Pull type utilising a matched pair of 2SB324 PNP transistors mounted to the metal chassis. The second problem was with the very low volume fuzzy sound. Therefore, I replaced the 2SA70 with an AF116, and that worked extremely well. Hence, as soon as the transistor terminals heated, the short cleared and I could hear a faint radio signal through my headphones. Soldering iron uses ceramic technology, which provides electrical insulation allowing me to work on current carrying circuits. Therefore, I simply applied some fresh solder to their terminals, and the transistor came back to life again. I was getting 2.07 V on the base and collector, which was leading me to think that there, may be in internal short in this transistor.įrom experience, I knew that heating the terminals of these old germanium transistors could sometimes clear their internal short. I would have expected at least 4 V to 5 V at the collector, but it was half of what it should be. ![]() I decided to measure the voltages at its terminals and note them down on scrap paper.īased on my semiconductor knowledge, and looking at these voltages, I could see that they were screwy. Intermediate frequency (IF) stages of radio circuits. I was vaguely familiar with the 2SA70 and knew they are usually found in mixer, oscillator, and Radio frequency (RF) signal enters the printed circuit board through a wire and passes through the first stage, which has this transistor. The trail began with transistor 2SA70 which is a PNP germanium transistor in a TO-70 package. Unfortunately, I was unable to obtain a circuit diagram for this radio, however, this Japanese heterodyne design is very straightforward, and I decided to rely only on my diagnostic skills to figure out what was wrong. I connected my headphones in the headphone socket and heard a very slight hiss indicating that perhaps the audio amplifier stage was just alive but barely. The National Panasonic T-100D was completely dead, and did not produce any sound from the loudspeaker. ![]()
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