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My Zenith H500 Transoceanic started to lose the upper frequencies. I checked and B+ was a bit down. The selenium was weak. It was about 40 years old at the time. I recommend carefully matching the voltage on the schematic to the radio/tv for protection of electrolytics. My TS-14 Motorola developed the "jitters" after I replaced the seleniums with silicon diodes. The B+ was around 45 volts too high acording to the schematic. I wasted a LOT of time checking the rest of the set until I ran the set on a variac and lowered the voltage and it started to behave. I put a 10 ohm 5 watt in series with each selenium to allow proper line voltage.
Since it had new electrolytics, they didn't get warm like some originals will while they reform.
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