01-10-2017, 08:07 PM
Thanks everyone for the replies! I will try to keep this brief, but let me give you an overview of where the radio is now.
I rebuilt the chassis with all new caps (not counting micas). All resistors have been changed with the exception of two dogbones which checked right on specs. The radio powered up fine, had good volume and was sensitive on all bands. All the tubes are good and checked 65% or better. After alignment I checked the voltages and had a problem with plates on the two 78s and 6A7 being high by about 40 volts and SGs on those being low by about 35 volts. Other voltage readings were close to specs with the exception of the cathode on the 78 IF which was 1.8 vs. 2.6 desired. I rechecked all wiring and component values and everything looked good. I was getting about 1.8 volts across the shadow meter at that time.
See schematic here: http://www.nostalgiaair.org/Resources/814/M0013814.htm
One problem here is the schematic (S) shows one value and the parts list (PL) shows a different one for some of the components (R22 S=2.0M, PL=1.0M), (R30 S=2.0M, PL=51K), (R50 S=99K, PL=20K) and (C51 S=.03mF, PL=.15mF). I originally went with the parts list values as that was what was originally in the radio. They made a change to R50 from 99K ohms to 20K ohms. I watched John's video series on his 630 he did a few years ago and on part 35/35 he had a similar problem with the voltage divider. He had found a change where the factory changed R49 to 10K and R50 to 20K. He ended up changing the value on R50 to around 40K to get his voltage back to where they are supposed to go. I think Philco changed the parts and maybe didn't update the voltage table. Not sure, maybe someone could comment on this? Anyway, I changed the values of the divider to R48 to 16K, R49 to 10K and R50 to 120K and now the voltages throughout the set are close to normal. The G2 grid on the 6A7 is about 25 volts low so I may have to play with the values some more. The radio plays very well and is a lot louder. I still need to realign it.
Now to the shadow meter. This is the same type that was discussed in a previous Phorum thread and pictures can be found here:
http://philcoradio.com/phorum/showthread.php?tid=2861
I'm not sure how this works either. I don't see a magnet in it anywhere. The vane has one ferrous rivet on one side that will attract to a magnet. The schematic shows a coil value of 500 ohms and mine ohms out at 598. Right now I'm getting around 4.5 volts on it and it will decrease by about 3.8 to 4.0 volts on stronger stations.
I guess right now I'm trying to figure out what the normal voltage swing should be across it for strong station and no station. Also, I can get it to move around if I put a magnet close to the vane, but it doesn't move otherwise. I guess the coil generates a magnetic field between the two poles on both sides of the vane, but not sure how its supposed to react unless that rivet was supposed to be magnetized. The adjusting screw in the back just bends a brass band toward the poles from the coil which I guess is supposed to change the magnetic field. I haven't been able to find much about this design at all other that the Phorum link above.
Radioroslyn mentioned the AVC voltage. Where would I read that on the radio?
Again, thanks everyone for the help. I enjoy working on these old Philcos and look forward to getting this one up and running. I've restored a Model 60, 66, 40-120 and a 46-1226.
Have a great day!
Mike25
I rebuilt the chassis with all new caps (not counting micas). All resistors have been changed with the exception of two dogbones which checked right on specs. The radio powered up fine, had good volume and was sensitive on all bands. All the tubes are good and checked 65% or better. After alignment I checked the voltages and had a problem with plates on the two 78s and 6A7 being high by about 40 volts and SGs on those being low by about 35 volts. Other voltage readings were close to specs with the exception of the cathode on the 78 IF which was 1.8 vs. 2.6 desired. I rechecked all wiring and component values and everything looked good. I was getting about 1.8 volts across the shadow meter at that time.
See schematic here: http://www.nostalgiaair.org/Resources/814/M0013814.htm
One problem here is the schematic (S) shows one value and the parts list (PL) shows a different one for some of the components (R22 S=2.0M, PL=1.0M), (R30 S=2.0M, PL=51K), (R50 S=99K, PL=20K) and (C51 S=.03mF, PL=.15mF). I originally went with the parts list values as that was what was originally in the radio. They made a change to R50 from 99K ohms to 20K ohms. I watched John's video series on his 630 he did a few years ago and on part 35/35 he had a similar problem with the voltage divider. He had found a change where the factory changed R49 to 10K and R50 to 20K. He ended up changing the value on R50 to around 40K to get his voltage back to where they are supposed to go. I think Philco changed the parts and maybe didn't update the voltage table. Not sure, maybe someone could comment on this? Anyway, I changed the values of the divider to R48 to 16K, R49 to 10K and R50 to 120K and now the voltages throughout the set are close to normal. The G2 grid on the 6A7 is about 25 volts low so I may have to play with the values some more. The radio plays very well and is a lot louder. I still need to realign it.
Now to the shadow meter. This is the same type that was discussed in a previous Phorum thread and pictures can be found here:
http://philcoradio.com/phorum/showthread.php?tid=2861
I'm not sure how this works either. I don't see a magnet in it anywhere. The vane has one ferrous rivet on one side that will attract to a magnet. The schematic shows a coil value of 500 ohms and mine ohms out at 598. Right now I'm getting around 4.5 volts on it and it will decrease by about 3.8 to 4.0 volts on stronger stations.
I guess right now I'm trying to figure out what the normal voltage swing should be across it for strong station and no station. Also, I can get it to move around if I put a magnet close to the vane, but it doesn't move otherwise. I guess the coil generates a magnetic field between the two poles on both sides of the vane, but not sure how its supposed to react unless that rivet was supposed to be magnetized. The adjusting screw in the back just bends a brass band toward the poles from the coil which I guess is supposed to change the magnetic field. I haven't been able to find much about this design at all other that the Phorum link above.
Radioroslyn mentioned the AVC voltage. Where would I read that on the radio?
Again, thanks everyone for the help. I enjoy working on these old Philcos and look forward to getting this one up and running. I've restored a Model 60, 66, 40-120 and a 46-1226.
Have a great day!
Mike25
