01-27-2014, 06:59 PM
Quote:Jamie, did you check or replace resistor 65 and cap 66? Thes parts in combination with the field coil comprise a resonant trap which is tuned to the 120 Hz ripple frequency. If the resistor is open or high, or cap is off tolerance, the circuit will not be tuned to the ripple freq and you will experience increased hum.
Placing the speaker in the cabinet results in increased hum because of the acoustic baffle effect. The low freq response of the speaker is increased and therefore the hum becomes more apparent and noticeable.
Ok, when I bridged the 8mfd cap with the 20mfd cap, the hum disappeared, but voltages went too high for comfort. (At least too high for me to use this radio very much). I have a feeling it will eat tubes. I just bridged the cap to try and track down the problem area, not as a permanent fix.
Cap 66 is a .3mf bakelite block. I stuffed that cap. It was replaced, but not resistor 65. I've been working all day, but I have tomorrow off. Tomorrow, I will recheck that resistor and report back. I think it was a resistor between two lugs on that same bakelite block. If so, I certainly checked it and would have replaced it, were it out of spec.
The speaker in the radio is the speaker that came in it when I purchased it. I do not know if it is the original speaker though. How would I know if it has a hum bucking coil? What do I look for? I can post a photo of the back of the speaker if needed. It looks like a typical 1930's Philco speaker. I can't see a part number on it.
The artist formerly known as Puhpow! 8)