Best to use the one from the library on this site, then when you refer to part 30 we know which part you are referring to. Of course any radio not a Philco you would have to provide a schematic or link to a schematic.
These tubes are local tubes and the base is kind of a shield. The center post of the tube socket should be wired to chassis ground for the shield to work. If you look at the second XXL in the schematic, you can see a dashed line just inside the tube, it is connected to ground. That's the center post. You will see components connected to the center post because it is a convenient ground terminal.
So you can see how Important it is to identify parts with the schematic, especially when you have multiple parts of the same value. When removing a part, connect a jumper wire with gator clips to each terminal so you have a reference where the new one goes.
"So you can see how Important it is to identify parts with the schematic, especially when you have multiple parts of the same value. When removing a part, connect a jumper wire with gator clips to each terminal so you have a reference where the new one goes."
Thanks Rod,
I definitely only replace one part at a time, that alone has been enough of a headache with this chassis.
I am back tracking on my resistors as the one that burned based on the old one's resistance was correct but another resistor that connects to the tube wasn't correct. I swapped them initially based on the schematic and a resistor chart. I am double checking with my pictures; there's only 14 so I'd rather be safe than sorry.
I believe I'm making progress, resistors have been rechecked and corrected, removed that ugly blue capacitor and more wiring. Powered it up, pilot lights are working, and the humming sound is still there but very faint compared to when I started. Now to the speaker and the Antenna.
Well guys I am stuck, frustrated and about ready to give up. For starters all I'm getting from the speaker is a humming sound no stations coming in.
Issues encountering now is resistor 42 has burned again but only after I reinstalled the blue capacitor removed yesterday. I reinstalled the blue capacitor because a new one installed in it's place popped today.
My problems seem to be around area 40 and 41 on the schematic. Capacitor 40 looks like a double 400volt, unless I'm missing itI don't see the blue capacitor on the schematic. My original picture shows #40 cap, blue cap and #41 resistor connected.
Earlier it was mentioned that cap 40 could be rebuilt. Can it not just be replaced with 2 450 caps? Today while testing the 2nd 450 cap which connects to resistor 42 and the speaker wire it eventually popped.
I've attached a before photo showing the #40 cap and the blue cap. Can someone let me know if the blue cap is seen on the schematic.
From what I see is the blue cap was added by someone after the radio was sold presumably to replace cap 40A. I can't tell if the original 40A had been removed from the circuit. In any case, you should remove original 40A and the blue cap and connect a 4.7mfd cap with the negative lead to ground.
I am assuming the black electrolytic cap in the last Pic is cap 40 and the center terminal of the strip is ground. Therefore, it appears cap 40 is connected backwards with it's positive lead connected to ground. When you do this you get the result you experienced, pop!! The 2.2k resistor should be connected between the positive leads of caps 40A and 40 as the schematic shows.
Whenever a new cap is connected across a defective one the result is a bigger defective cap.
Take your time and carefully remove the old caps from the circuit then connect the new caps in the correct polarity. Test the 2.2k resistor, it may be okay. If the resistor gets hot then there's a problem with one of the circuits that is connected to cap 40.
Thank you Rod and Paul
I took a break, did some yard work and Rod "Therefore, it appears cap 40 is connected backwards with it's positive lead connected to ground." this is the first thing I will check. I apparently misunderstood just radios that polarity didn't matter with the new caps (Axial). I guess it doesn't matter with the paper caps. I take it that the black groved end is the positive side? If this is the case I'll need to check the others installed.
If you check my post #49 it shows the completed chassis with 2 new caps for #40 and hopefully #40A. Blue cap removed, I had it on a few yesterday and the day before. I am definitely starting with the polarity checks.
Sorry, I got really busy in May and haven't seen your thread in a while. I am VERY sorry about that.
Stick to it and you will get this to work. A couple of things that may help you:
One must pay attention to both polarity and working voltage for any electrolytic capacitor, new or old, axial or radial wet or dry.
It was common for people to " bridge" old electrolytic caps with new ones. This is why that blue cap exists. It was bridging one section of that paper electrolytic 2 section capacitor. Take them all out and replace with originals.
Electrolytic caps can either open or short as they get old. The "dry" type tends to open. The wet ones often short. When installed backwards or working voltage is exceeded electrolytics overheat, short and explode. C40 being installed backwards could have taken out the resistor.
As stated before, one does not have to match the stated voltage of non-electrolytic caps to the actual voltages encountered; order the highest voltage rating available. For restoring old radios, ordering caps with a voltage rating of 630V is best.
In addition to all the other problems with this radio, you also have to deal with the crumbling rubber insulation. This can be done either by replacing the entire wire or by cutting only 1 end and slipping some heat shrink tubing or "spaghetti" over the conductor.
If repairing a radio but not intending to make a museum piece, replace capacitors and resistors by cutting the wire at the part itself, not at the terminal or socket connection. Bend the remaining lead wires into a hook, and install the leads of the new wire into these "hooks" and hook the new wire into the old, crimp and solder. This way, you don't have to heat up a terminal on a terminal strip or tube socket.
I have both pencil type soldering irons and a Weller soldering gun. Each have their place, but for this type work, a 40 watt pencil may be better suited than the Weller gun for this job. Tip condition, shape, cleanliness and tinning are important to any soldering iron or gun. For this work, a chisel tip may be best. The idea in soldering is to "heat the work, not the solder. There is nothing wrong with touching solder to the tip at the work to get the heat to conduct and melt the existing solder on the joint, but heating the joint is the whole idea. the end result is a smooth joint with good mechanical connection before adding the solder. When replacing multiple components on the same terminal, if the "hook" method described above is not used, desoldering, removing all wires from the connection, crimping all components to the connection and resoldering is the way to go. I tend to use the thinnest 60/40 solder available.
Having specifications and pin diagrams for the tubes used in a radio are very important, especially when the "pinouts" are not listed on the schematic, as is the case here. The RCA Receiving Tube Manual is a vital reference for anyone in this hobby. It is available in several editions. For this set, the RC16 version, published in 1947 is a good source of information. This version can be found on the internet. For your convenience, I have attached the pin diagram for the 7B5 Audio Output tube and the 7Y4 Rectifier are attached below:
Per these diagrams, the black or blue wire from the audio output transformer goes to Pin 2 of the 7B5 output tube. The Red Wire goes to B+, the junction of C40A (red wire on the original cap), Pin 3 of the 7B5 output tube, the output of the speaker field coil and several resistors, wires, etc. The other field coil wire goes to the cathode of the 7Y4 Rectifier (Pin7) along with the positive lead of C57,, the 18 uF cap.
Note that the "inactive" pins on some tube sockets (pins that have no connection to an element of a tube) are often used as terminals where wires or componeints such as caps and resistors are joined. Do not let this confuse you.
When troubleshooting, "divide and conquer" inject an audio signal such as the output of an MP3 player CD or cassette player, etc between chassis ground and the ngrounded "leg" of the volume control. If the sound output is good, then troubleshoot the detector, IF, convertor and F sections of the radio. If n o sound, troubleshoot the audio and power supply circuits.
Hoep that all of this helps.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
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