NEED HELP WITH G.E. MODEL GD-60 WIRING

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NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Tue Feb 01, 2011 9:46 pm

I have completely replaced all the rubber coated wiring and caps in this 1938 GE GD-60 radio but I only get a steady hum with power and after a few seconds the ballast tube gets quite hot. I think my problem is the proper wiring on the electrolytics. The old filter pack had no markings so I assumed black to be neg. It had a 12 and 20 mfd filters. I put in a 16 and 20. I have a red wire from the 16mfd going to the cathode of the 25Z5, yellow wire from the 20 mfd going to the ballast tube and the black as common neg going to the cathode of tube 6A8 which doesn't seem right to me. My schematic is very hard to make out but it looks to me like the neg side of the filters should be on the cathode of the 25Z5 which would be the red wire. Tried subbing in the old filter pack and I got a bird chirping sound as I turned up the volume. So are my new filters wired up wrong or is the ballast tube bad? Hoping someone on the forum here has worked on one of these and can help.

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by Bill Cahill on Wed Feb 02, 2011 12:48 am

Don't put negative on 25Z5!
That's B+!
Sounds like wrong wire is on 6A8. Seems that should be Positive yellow wire, low voltage.
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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by Nick666 on Wed Feb 02, 2011 5:17 pm

Can you post a link to the schematic and pics of what you have done.

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Wed Feb 02, 2011 7:17 pm

Nick, Here's a link to the schematic ...
http://www.nostalgiaair.org/Resources/883/M0007883.htm
The filters are C30 & C31 by the 25Z5 tube diagram. Right now I have the filters out of it. I agree , Bill , that it would not seem right to have the neg on the 25Z5 but the schematic makes it look like the two filters are together on a common line to the 25Z5 so I am confused!! So any thoughts on the ballast tube. Should be 170ohms and I'm measuring about 125 on the 3 & 7 pins.

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by Bill Cahill on Wed Feb 02, 2011 7:50 pm

According to the schematic the ballast only has one resistor, and, that's in hot end of ac filament supply.
One .02 paper cap goes from that to junction of C34 on other end of field coil. Field, and, two resistors are in negative ends of electrolytics.
All positive ends tie together, and, go to various circuits, including rectifier.
Cathode of 6A8 indeed gets a black wire going to the other end of negative supply.
This radio is biased in negative supply, instead of positive end.
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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Wed Feb 02, 2011 9:22 pm

Thanks Bill for clarifying the schematic. I was having a hard time reading it and understanding it. At least you have confirmed that I had them in right. I'll put some different filters in and try that. Maybe I had a bad one.

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Thu Feb 03, 2011 7:46 pm

I did put in a different set of new filter caps and I got a slight improvement. I can now pick up a garbled station with a 20' coiled up antenna wire. I still have a pretty loud hum though and the ballast is still very hot. I've checked all the resistors and most are close to specs. Just not sure why the current isn't a smooth DC. If I had another ballast tube I would try that. Maybe I will temporarily try a 10w resister in its place and see how that affects it. Should I try a larger electrolytic?

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by Bill Cahill on Thu Feb 03, 2011 8:13 pm

My guess is you may have wired something wrong.
Also, ballast tubes get very hot, and, this is for the filament supply only.
I'd check all the power supply wirring very carefully.
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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Thu Feb 03, 2011 10:51 pm

I did pull apart the ballast and it looks like new with no burn spots. I also tried a larger filter but no change. So I'm thinking the same, Bill Cahill, that I may have crossed up something. I did take photos before I started so I will start checking each new wire. Thanks for the help.

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by bill57 on Sat Feb 19, 2011 11:38 pm

Update on this....I did find a short in the push button assembly from old wiring. I had not redone this part so I replaced all the wiring to the buttons and now it is receiving stations fine with a long 20' wire antenna. However I still have a loud hum that stays steady and does not change with the volume or changing stations. I tried a slightly larger filter cap(16 to a 20) and it helped a little. I've tried different tubes, checked all resistors but just can't quiet it down. Any other suggestions??

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

Post by sprman on Sun Feb 20, 2011 12:34 pm

Make sure nothing is shorting too ground and you have no cold solder joints.Placement of wires can cause hum too, as will a tube thats bad..Sprman : )

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Re: NEED HELP WITH G.E. MODEL GD-60 WIRING

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