September 19, 2012 at 3:02 pm #3474BruceForum Participant
I have an old Marconi Radio/Phonograph (I don’t know the model). I am trying to get the Phonograph part to work. The radio comes on after the tubes warm up, the volume on the radio goes quite loud and there is a hum which I am guessing is an old tube. When I switch the knob to Phono (the turntable spins and I am able to drop the needle onto the record) I get sound from the speakers if I tap the red wire going to the needle cartridge but no sound from the speakers when the needle is placed on the record. I have replaced the needle cartridge (I have 3, 2 I have recently bought). One day I did hear a faint sound from the record through the speakers but that lasted a very short time and I was never able to get sound from the record again. Anyone have any ideas what is going on? Is the tube too old? Is the ground wire to the needle cartridge faulty? Something else?September 21, 2012 at 1:35 pm #3480Dan WalkerCVRS Member
Bruce ,,I am certqinly no expert in this area ,but it sure sounds like you need to replace the electrolytic caps. in this unit.. That is most likley the cause of the hum,,more likley than a bad tube.If the caps are bad it could damage the power supply.
Next I would check all the connections and make sure they are making contact.. It might be a cold solder joint.. That is where the solder is in place but it has not made good contact.. Also ,,the switch that controls RADIO/PHONE should be cleaned as it may not be making contact.
Because you did get sound at one time makes me think that there is a loose connection
I find that as a beginner,I go over everything to see if all the wirese are making connected.. You can purchase capasitors at” Just Radios”’.I do hope this helps Dan in CalgarySeptember 24, 2012 at 4:27 pm #3484BruceForum Participant
The hum I’m not too worried about right now, it’s only when the volume is up almost al the way.
The Radio/Phono switch is working, like I said I get sound from the live red wire leading to the needle cartridge.
I’ve tried checking all the connections but they all seem to be fine.October 14, 2012 at 7:55 pm #3527JagtechForum Participant
Those old crystal cartridges have a finite life, and an unused one can expire from old age even just sitting on the shelf. It sounds like your cartridge is bad, as you are getting some audio response when you touch he cartridge wires. That indicates the amplifier is working. Its getting hard to find “fresh” crystal cartridges.October 17, 2012 at 3:42 pm #3529Don EdwardsForum Participant
Hi: New to this site but not new to old radio service. It does indeed sound like the cartridge is bad, because touching the wiring at the back of the cartridge and getting hum does indeed indicate the amp is ok. You can find ceramic cartridges online at reasonable cost. My favourite supplier is myneedlestore.com. He is in Quebec and has some stereo ceramic cartridges available. The only problem is that generally ceramic cartridges put out from about 100mv to .5volt and crystal cartridges put out usually over 1volt. That may leave you with a lower volume when playing records. I have found this when I have replaced old defective cartridges. Hope this helps.
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