06-24-2011, 09:33 AM
The cathode of the 6X5 is pin 8. You can get a pin-out diagram here: http://www.nostalgiaair.org/ Click on "Tubes" and then type 6X5 in the search box that says "Type" over it.
Looking at the bottom of the socket with the chassis upside down, you count the pins clockwise from the slot in the socket. Pins 4 and 6 are not shown in the diagram because nothing connects to them, but they are there in the socket, so count 'em anyway. Pin 8 is the pin to the right of the slot if the slot is pointing right at you.
If all caps are good, and if there are no shorted wires, you should get infinite resistance between the cathode and ground. (Somebody correct me if I'm wrong about this.) Your reading might be lower for a few seconds while the electrolytics charge up, but after that your reading should be infinity or "OL" on a digital ohmmeter.
If you see any path to ground (resistance other than infinity), you could test all three electrolytics by disconnecting the positive side and measuring resistance across the cap. It should be infinite. This is not a perfect measurement for leakage, since in operation there is high voltage across them (depending on which cap) but it is better than nothing.
If your multimeter will measure capacitance, try that. Are the electrolytics rated for 450 volts?
There are a few possible sources other than the electrolytics for B+ shorting. I'm pretty sure that each of the IF transformers has rubber wire inside which could short. I always take the IF cans out to replace all the wires and test any components inside. If you read a short with your meter, you might try wiggling the wires going into the cans to see if it makes a difference. If it does, replace or re-insulate the wires.
It is unlikely, but the plate or screen grid in another tube could be shorted. It might be a good idea to test all of them. I've had tubes short spontaneously, and I once caused one to short by putting it in the wrong socket. It is not unheard of that a tube will short when it is handled, even gently.
Sometimes shorts show up when a chassis is moved, even when it operated correctly beforehand. I remember a restorer on another forum whose radio (not a Philco) would operate fine on the bench but shorted every time he put it in the chassis. Because of the rubber wire, your chassis is probably especially vulnerable to intermittent shorts.
Looking at the bottom of the socket with the chassis upside down, you count the pins clockwise from the slot in the socket. Pins 4 and 6 are not shown in the diagram because nothing connects to them, but they are there in the socket, so count 'em anyway. Pin 8 is the pin to the right of the slot if the slot is pointing right at you.
If all caps are good, and if there are no shorted wires, you should get infinite resistance between the cathode and ground. (Somebody correct me if I'm wrong about this.) Your reading might be lower for a few seconds while the electrolytics charge up, but after that your reading should be infinity or "OL" on a digital ohmmeter.
If you see any path to ground (resistance other than infinity), you could test all three electrolytics by disconnecting the positive side and measuring resistance across the cap. It should be infinite. This is not a perfect measurement for leakage, since in operation there is high voltage across them (depending on which cap) but it is better than nothing.
If your multimeter will measure capacitance, try that. Are the electrolytics rated for 450 volts?
There are a few possible sources other than the electrolytics for B+ shorting. I'm pretty sure that each of the IF transformers has rubber wire inside which could short. I always take the IF cans out to replace all the wires and test any components inside. If you read a short with your meter, you might try wiggling the wires going into the cans to see if it makes a difference. If it does, replace or re-insulate the wires.
It is unlikely, but the plate or screen grid in another tube could be shorted. It might be a good idea to test all of them. I've had tubes short spontaneously, and I once caused one to short by putting it in the wrong socket. It is not unheard of that a tube will short when it is handled, even gently.
Sometimes shorts show up when a chassis is moved, even when it operated correctly beforehand. I remember a restorer on another forum whose radio (not a Philco) would operate fine on the bench but shorted every time he put it in the chassis. Because of the rubber wire, your chassis is probably especially vulnerable to intermittent shorts.
John Honeycutt
