Hello everyone! Im new to the forum here. I acquired my grandparent's Philco 46-1209 radio/phono console and have been progressing through a restoration for it. I have replaced the two can caps in the chassis with Axials of the same uF rating and voltage, plus i have replaced all the wax paper in oil caps in the chassis. I fired it up yesterday and she works! However I am getting a 60hz hum that does not go away with tuning, volume, etc.
Also my reception is weak. I can pick up some stations, but with the volume maxed out im getting very little output - probably just barely above conversation level. And im getting almost no reception in the shortwave setting.
I tested the phono player, works great - when i turn up the volume on it, it seems to get plenty loud.
Any help would be great! Attached are some photos.
I have a 47-1230 - the big brother of your radio. Similar, more bands.
Do you always have a hum, or just in some of the bands? e.g. do you have it in AM and shortwave, plus phono?
On mine, the phono did not work, but its transformer was causing a bad hum. I ended up disconnecting it to restaure the AM and FM radios. I still can't pick up shortwaves, but that might not be a technical problem (no suitable antenna might mean no signal)
I have a 47-1230 - the big brother of your radio. Similar, more bands.
Do you always have a hum, or just in some of the bands? e.g. do you have it in AM and shortwave, plus phono?
On mine, the phono did not work, but its transformer was causing a bad hum. I ended up disconnecting it to restaure the AM and FM radios. I still can't pick up shortwaves, but that might not be a technical problem (no suitable antenna might mean no signal)
you seem to have done a nice job on the recap.
Thanks. Yes it does hum regardless of the phono/SW/AM setting.
Ive checked voltages against a voltage chart that is posted within the schematics. Everything looks to be close to posted voltages, except one of my 7H7s has a cathode voltage reading of 2.4V - according to the chart its supposed to be .7 volts. is this too far off? And if it is what does that mean?
Ok so i did some more checking. if I pull the tube right before the phase inverter (7X7) hum goes away. i put it back in and pull both of the IF stage tubes (7H7) it still hums with those tubes in, but not with the 7X7. maybe the hum issue is between those two tubes?
How would i hook up my scope to the output of this radio? i see 4 wires for the field coil speaker - I have the amp out of the cabinet and away from the speaker, could i hook up a dummy load between the green and white wires of the speaker connector and connect my scope across that? do the other two wires have to be connected to anything in order for it to work? Ive never dealt with field coil speakers before, that is why i am asking.
You need to have all wires of the speaker connected for the radio to operate. The field coil of the speaker also acts as a power supply choke to filter the DC output voltage. To do any testing of the radio outside of the cabinet, you need to remove the speaker also and connect it to the chassis.
Looking at the photo of the underside of the chassis, I see only one replacement electrolytic. Did you also replace the other two? If not, this might be the cause of your hum?
(This post was last modified: 11-06-2014, 06:07 PM by Mondial.)
Yes I've replaced all three 'lytics, the others are probably sticking through the hole where the cap can used to be.
any reason I can't substitute in a 10 - 15W resistor for the choke, just for testing purposes? This way I reckon I could bench test the amp without it being hooked to its speaker with a proper dummy load.
Are you sure you have the electrolytics wired correctly? Something does not look right in the photo. According to the schematic, the negative of the 20 uF capacitor C49 should be connected to R37 mounted on the chassis. The photo shows a 10 uF connected there instead. The 10 uF and 25 uF caps should have their negatives connected directly to chassis. Only the 20 uF cap should connect to R37.
You could substitute a resistor of equal resistance for the field coil, but it will increase the hum level as it is not as efficient as a filter. Since you are troubleshooting a hum problem, it might not be the best way to test. Why not just connect the speaker and measure output at the voice coil itself?
I was just curious as to how i could bench test my radio without having to pull the cabinet.
I double checked my electrolytic wiring to the schematic. I am wired properly there. The hum is definitely 60hz or so, i can hear it before anything else warms up enough to come on.
Also, how loud do these radios get? I cant seem to get a signal level above "raised voice" level. Could this be due to a faulty output transformer? Ive injected signal into the grid of both the phono preamp and the PI stage, and im getting roughly the same audio ouput level.
