09-30-2009, 10:52 PM
The radio works wonderfully except for a noisy volume control. The one reference on radio servicing that I have says replace the pot. That may have been a good idea in 1940 but I've tried to find similar ones today and come up blank. Three tabs hold the housing on pot. I'll have to desolder a 33 pf capacitor to remove the cover. Bill Turner's Dial Cover provides a nice review but it's the only one I've found. Perhaps no others are needed. Funny thing is that I could just about throw a rock and hit his house from my back yard. Small world.
The volume control is not always noisy so I'm not sure if I should mess with it. Any suggestions would be welcome.
I spent several hours working cleaning and lubricating the coarse and fine tuning shafts and the band selector. The tuning shaft would have been a major project to remove so I opted to use a small amount of Liquid Wrench and a couple of drops of Marvel Mystery Oil to loosen the dried up lubricant in the shaft. Both turn freely and independently now. The band selector is almost a mechanical engineering marvel. The dial face on the radio is an inverted, U with short legs pointing down. The dial is a round disk with the five bands printed on it in a pinwheel pattern. The selector knob is a pivot point with two levers that's connected to the range selector switch shaft and a gear that turns and clicks the the dial in one of five positions. There are six points that must rotate freely for the selector to work. I had to remove the dial and polish the shaft and hole with 0000 steel wool before lubricating it with a very small dab of lithium-based grease and a drop of MM Oil. All rotation points were oiled and alignment was checked to minimize binding. It turns freely but requires a good grip on the knob to make the change.
The person that used the radio listened to a lot of shortwave. There's a spot on the long wave band of the dial that's faded. When the radio is set to listen to short wave, that spot is directly above a lamp.
Al long wire connected to the A1 terminal provides great reception.
Still bothers me that I couldn't read the schematic well. - simple things too like grid voltages need to be negative. I have a lot of facts that are isolated now. Perhaps they will come together in time. On the bright side, I was able to replace worn out wires and most of the capacitors and resistors without incident buy clipping or desoldering all of the components at a node and solder the new replacements in place before moving on. Only one silly mistake. The radio wasn't working after I reassembled it and installed the old tubes. All of the tube voltages were good and a little higher than spec. Thank you agina, Ron, for explaining that this is normal and OK. A 200 Hz signal on the audio grids showed that part of the circuit was working fine. After a day or two of looking at the wiring and documenting the voltages at the nodes I notice a desoldered lug with nothing attached. A loose end of a wire that's connect the the third IF coil was hiding under two wires against the chassis. When that wire is not connected you get nothing. Connect it and the radio works.
On to the cabinet now. I want to the ethanol to remove the old finish. This could take some time.
One thing I must comment on is the dial cover. It's plastic, not glass. Did RCA really spend all of the time an money to make such a fine radio and use a plastic dial cover that yellows and scratches over time?
The volume control is not always noisy so I'm not sure if I should mess with it. Any suggestions would be welcome.
I spent several hours working cleaning and lubricating the coarse and fine tuning shafts and the band selector. The tuning shaft would have been a major project to remove so I opted to use a small amount of Liquid Wrench and a couple of drops of Marvel Mystery Oil to loosen the dried up lubricant in the shaft. Both turn freely and independently now. The band selector is almost a mechanical engineering marvel. The dial face on the radio is an inverted, U with short legs pointing down. The dial is a round disk with the five bands printed on it in a pinwheel pattern. The selector knob is a pivot point with two levers that's connected to the range selector switch shaft and a gear that turns and clicks the the dial in one of five positions. There are six points that must rotate freely for the selector to work. I had to remove the dial and polish the shaft and hole with 0000 steel wool before lubricating it with a very small dab of lithium-based grease and a drop of MM Oil. All rotation points were oiled and alignment was checked to minimize binding. It turns freely but requires a good grip on the knob to make the change.
The person that used the radio listened to a lot of shortwave. There's a spot on the long wave band of the dial that's faded. When the radio is set to listen to short wave, that spot is directly above a lamp.
Al long wire connected to the A1 terminal provides great reception.
Still bothers me that I couldn't read the schematic well. - simple things too like grid voltages need to be negative. I have a lot of facts that are isolated now. Perhaps they will come together in time. On the bright side, I was able to replace worn out wires and most of the capacitors and resistors without incident buy clipping or desoldering all of the components at a node and solder the new replacements in place before moving on. Only one silly mistake. The radio wasn't working after I reassembled it and installed the old tubes. All of the tube voltages were good and a little higher than spec. Thank you agina, Ron, for explaining that this is normal and OK. A 200 Hz signal on the audio grids showed that part of the circuit was working fine. After a day or two of looking at the wiring and documenting the voltages at the nodes I notice a desoldered lug with nothing attached. A loose end of a wire that's connect the the third IF coil was hiding under two wires against the chassis. When that wire is not connected you get nothing. Connect it and the radio works.
On to the cabinet now. I want to the ethanol to remove the old finish. This could take some time.
One thing I must comment on is the dial cover. It's plastic, not glass. Did RCA really spend all of the time an money to make such a fine radio and use a plastic dial cover that yellows and scratches over time?
