One thing I hate, along with the 23,419 other things in my life, is having to repair my own test gear. You very rarely get asked to set up a FM VHF radio, tuner….. but when you do, a simple bit of kit like this RCA stereo simulator is a good thing to have in your back pocket. Meteorologically speaking, a big back pocket.
This box generates a 100mhz signal with a 19khz stereo pilot etc… Had this for years, it’s a US 110V bit of kit so needs an autotransformer. Modern FM radios have one chip that does everything and all the tuning and stereoicity is done in that. Sometimes get asked to repair a VHF FM radio, or tuner, valve, discrete or otherwise. Most of the time, you can get away with setting up by ear, but one tuner that came in was a pig. Asi que, pensé, out with the RCA box, plugged into the only 110V autotransformer I could find. Started to dismantle the tuner. 10 mins later, was aware of a hot sweaty component smell. The sort of smell that means trouble and, was coming from Mr RCA. Off with it’s case and found the main smoothing capacitor was hotter than a hot thing on the hottest day of the year. Removed all it’s wiring, a quick trip to Farads R us and fitted 3 electrolytics. HT is this set is around 160V and is half wave rectified, bit odd. We now had RF output and modulation. Pero, no 19Khz pilot tone, that section was not oscillating. This section is quite straight forward with a 12AT7 (ECC81 if you are this side of the pond) and a 19Khz crystal. Components and valve checked out so became upset at the thought of trying to find a 19Khz crystal…impossible. Hunted in the crystal box and came up with a 1.3Mhz something or other. Popped it in and yep, it was running. If I want to test stereo, I would have to either have to make a 19khz solid state oscillator or find some quartz, file and tin foil to make my own new crystal. In for a penny, I unsoldered the can of the faulty crystal. Resoldered the 4 pig-tail wires to the structure and, it worked! 2 hours of wasted time. Then nothing…The autotransformer went pop. My fault, looking at it’s rating, 20VA. The RCD box wants many more Ergs than that.