10-24-2013, 01:43 PM
If it is installed correctly and operated within its voltage rating, then its probably a bad cap or the radio is drawing excessive B+ current.
You can check the current draw by measuring the DC voltage across the field coil. If it is more than 50 or 60 V then the drain might be excessive due to a leaky coupling cap between the 75 tube plate and the 42 grid. A leaky cap here will throw off the bias and cause the 42 to draw excessive plate current.
If the drain is normal them the cap is probably bad with a high ESR. This is the internal series resistance within the cap, and causes heating with a high ripple current as found in the circuit as connected right after the rectifier.
You can check the current draw by measuring the DC voltage across the field coil. If it is more than 50 or 60 V then the drain might be excessive due to a leaky coupling cap between the 75 tube plate and the 42 grid. A leaky cap here will throw off the bias and cause the 42 to draw excessive plate current.
If the drain is normal them the cap is probably bad with a high ESR. This is the internal series resistance within the cap, and causes heating with a high ripple current as found in the circuit as connected right after the rectifier.
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