06-21-2007, 11:20 AM
hello, first sorry for my poor english. I will try to be as clear as possible...
I've bought a model 640 code 121 last week in france. it was a model specially design for french user. Everything is written in french on this philco.
I've downloaded the schematic of model 640. I've seen the bias is made with cathode resistor on the 78 RF, on the 6A7 and on the 78 IF.
On mine, it's different. all the cathode of this tree tubes are directly connected to ground. The CAG (you say AGC I suppose ???) is going first to the 78 IF and the 6A7 and in a second part to the 78RF.
Another thing. I've got a different resistor on the negative side of the transformer (the middle point between the to winding). On the original schematic, we've got a double resistor with one side to ground, the middle side is 60 ohms (for the 6A7 bias) and the other side is 160 ohms (60 + 100 ohms) for the 42 bias before the inter-stage transformer.
On mine, I've got a third point between ground and 60 ohms, approximately 24 ohms. There's a wire with start here and go to the AGC to maintain a minimum of -4V on all the grids.
My question is why does my radio is different from the model 640 ? Is there some modification for radio send to france ? The resistor,with the third point is an original part from philco and not an add-on.
Do you know 640 radio with all the cathode to the ground ???
Best regards
frederic ABIGNOLI
I've bought a model 640 code 121 last week in france. it was a model specially design for french user. Everything is written in french on this philco.
I've downloaded the schematic of model 640. I've seen the bias is made with cathode resistor on the 78 RF, on the 6A7 and on the 78 IF.
On mine, it's different. all the cathode of this tree tubes are directly connected to ground. The CAG (you say AGC I suppose ???) is going first to the 78 IF and the 6A7 and in a second part to the 78RF.
Another thing. I've got a different resistor on the negative side of the transformer (the middle point between the to winding). On the original schematic, we've got a double resistor with one side to ground, the middle side is 60 ohms (for the 6A7 bias) and the other side is 160 ohms (60 + 100 ohms) for the 42 bias before the inter-stage transformer.
On mine, I've got a third point between ground and 60 ohms, approximately 24 ohms. There's a wire with start here and go to the AGC to maintain a minimum of -4V on all the grids.
My question is why does my radio is different from the model 640 ? Is there some modification for radio send to france ? The resistor,with the third point is an original part from philco and not an add-on.
Do you know 640 radio with all the cathode to the ground ???
Best regards
frederic ABIGNOLI
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