Quote:
Originally Posted by vortalexfan
Yes, I've always wanted a 1920s radio so that my radio collection could be rounded out to include all of the various style of radios ever made over past 100 years.
One question Tim, did your radio when you powered it up make a high pitched whistling noise out of the speaker while it was warming up?
The reason I ask is because my radio when its first powered on and while its warming up makes a high pitched whistling noise out of the speaker before finally putting out an audio signal.
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The reason is that your detector tube , which should be a #27 if I looked at the right schematic , is an indirectly heated cathode type of tube , whereas your #80 B+ rectifier and #71A audio output tubes are directly heated cathodes . When you turn the power on the directly heated cathode tubes are conducting pretty much instantly VS the one indirectly heated cathode taking it's sweet time to begin passing signal . For all that time you have the audio amp section operating wide open but with no signal to process . In the absence of signal to force a bit of bias onto the circuit the tubes become very sensitive to "Microphonics" , having loose elements in the tube actually rattle and give off squeals . This is of course assuming that you did a full recap on the radio (haven't kept up with the entire thread here) because an electrical cause could be if the capacitor listed on the schematic as "43 - By pass condenser .002 mfd." were bad that could cause the amp to squeal till the detector warmed up and began supplying it with audio as well .