03-16-2019, 11:12 PM
as to the IF coil I fried, if all else fails, read the instructions! seems the Crosley service manual spells out, in bold print no less, UNDER NO CIRCUMSTACES SHOULD A GROUND BE CONNECTED TO THIS RECEIVER. in other words, USE AN ISOLATION TRANSFORMER before connecting a [grounded] scope to the chassis. even so, even after using an isolation transformer, I connected the scope ground to the neutral wire. maybe someone can tell me if I was well-advised to do that. or not. I say neutral wire because the isolation transformer has a polarized outlet.
as to the hum, I discovered [with a scope] that the signal from the audio transformer [with the antenna disconnected] looked like a sine wave with the peaks flattened a bit. unlike the signal from a radio that didn't hum. those peaks were narrow and pointy. I switched transformers and NO HUM! while I am pretty much a rookie, at fixing 120V radios anyway, I've never had a transformer cause a hum. nor read any mention of it. i'm curious to know what might be "wrong" with the transformer. the resistances are good. and it did work but introduced the hum even with the volume turned down.
thanks as always.
PS I put an X-Y cap across the AC line. it had no effect on the hum.
PPS the reception was poor because the solder joint on the antenna lead to the stator side of the tuning cap was loose. something this rookie discovered entirely by accident.
as to the hum, I discovered [with a scope] that the signal from the audio transformer [with the antenna disconnected] looked like a sine wave with the peaks flattened a bit. unlike the signal from a radio that didn't hum. those peaks were narrow and pointy. I switched transformers and NO HUM! while I am pretty much a rookie, at fixing 120V radios anyway, I've never had a transformer cause a hum. nor read any mention of it. i'm curious to know what might be "wrong" with the transformer. the resistances are good. and it did work but introduced the hum even with the volume turned down.
thanks as always.
PS I put an X-Y cap across the AC line. it had no effect on the hum.
PPS the reception was poor because the solder joint on the antenna lead to the stator side of the tuning cap was loose. something this rookie discovered entirely by accident.