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This six tube restoration comes from a Ham Fest. On inspection before dim bulb testing the chassis shows repair attempts. There are a few capacitors that have been replaced. The Diode bridge had been replaced with four silicon diodes in a plastic pill box. This will be replaced with a terminal board and dropping resistor or something more substantial. There is heavy corrosion of the fuse and just about all electrical contacts. The power switch shoes high resistance when closed and may need replaced if cleaning does not help. The power cord has been kindly cut off.
I clipped a cheater cord onto the transformer primary, plugged the cheater into a 100 watt dim bulb tester and applied power. The lamp stayed dim and the radio began to crackle to life. Once on direct line power the radio picked up stations on the AM broadcast and FM bands. Rather distorted but this is a great sign. No worries about IF transformers and the tubes are functional. The selector switch is in need of a complete cleaning as indicated by extreme crackling when the slightest tough or vibration occurs. There was no evidence of sound coming from the left or right tweeters. The EM80 tuning eye indicator is dark.
There looks to be a missing choke on the under side of the switch assembly. This will have to be investigated and replaced. The whole chassis need be compared to a chassis for any other modifications. It turns out these are two long wave band alignment capacitors. The fine wire coiled around the thick enameled copper stub needs to be wound or unwound to adjust the capacitance.
Further inspection shows many capacitors are original. There is a burnt original resistor in the audio section. Perhaps an output tube shorted or is shorted. This will be thoroughly investigated during restoration. Also an extended burn in period is to be run to shake out any bad parts (i.e., the corroded and rusted power transformer.
Silver Mica capacitor Disease The crashing thunderous roar in the AM band.
After hours of burn-in this radio developed static. It started as an occasional pop. Like the sound you get when some one turns an appliance on or off. It just progressively worsened. And the eye tube seemed to be fluctuating with the AM modulation. So I embarked on the delicate task of disassembling the IF cans, removing the internal mica wafers and adding external silver mica 600 volt caps. Join me below.
Now for a quicker way to remove the mica wafers.
The sensitivity all bands increased dramatically. I picked up several beacons on the long wave band below 350khz. The eye tube stopped bouncing to the music. FM was unaffected. There are not caps in the FM IFs.
It helps to use an earth ground with the LW reception. There are no RF bypass caps in this chassis. Besides to bypass (ground) LW may permit too much AC line current leakage.
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