The original "low hum" I thought I heard the other day I'm not hearing now. There is no sound at all. When I touch the middle terminal of the volume switch I don't hear anything either. All resistors seem reasonably close to what they should be. I replace elecrolytics, but found no mass of paper capacitors in this chassis to replace. I checked voltage at the specified points on grid plates and found a problem. I get slightly low voltage at the rectifier tube, then no voltage on any other plates. the field coil is getting very warm (is this normal). I'm not sure if this means that it is working or not, or how to test it or the output transformer to see if they are good/bad. I am an amateur with these radios, and this one is definately over my head.
Mike

Mike

Since the field coil is getting hot but you have no voltages something is shorted. Are electrolytic caps in the right direction? A reversed electrolytic will act as a short. Check this first.

Rectifier voltage is low because the shorted item in loading it down.

Philco used block caps in most of their radios. That's why you don't see many paper caps. These caps will be in black bakelite packages mounted to the chassis.

Here is some information:

http://www.philcorepairbench.com/bblokcap.htm

After you have voltage on pin #3 of the 42 tube measure pin #2. If it has voltage the output transformer should be ok.

http://www.nostalgiaair.org/PagesByModel/876/M0013876.pdf

Norm

:The original "low hum" I thought I heard the other day I'm not hearing now. There is no sound at all. When I touch the middle terminal of the volume switch I don't hear anything either. All resistors seem reasonably close to what they should be. I replace elecrolytics, but found no mass of paper capacitors in this chassis to replace. I checked voltage at the specified points on grid plates and found a problem. I get slightly low voltage at the rectifier tube, then no voltage on any other plates. the field coil is getting very warm (is this normal). I'm not sure if this means that it is working or not, or how to test it or the output transformer to see if they are good/bad. I am an amateur with these radios, and this one is definately over my head.
:Mike

:The original "low hum" I thought I heard the other day I'm not hearing now. There is no sound at all. When I touch the middle terminal of the volume switch I don't hear anything either. All resistors seem reasonably close to what they should be. I replace elecrolytics, but found no mass of paper capacitors in this chassis to replace. I checked voltage at the specified points on grid plates and found a problem. I get slightly low voltage at the rectifier tube, then no voltage on any other plates. the field coil is getting very warm (is this normal). I'm not sure if this means that it is working or not, or how to test it or the output transformer to see if they are good/bad. I am an amateur with these radios, and this one is definately over my head.
:Mike

How many Ohms do you read from the rectifier cathode to ground (set off, unplugged, etc)? Is a filter capacitor in backwards? Unplug the field and measure the field coil to the frame, then measure each chassis lead frothe field coil to the chassis. Look for something reading below several thousand Ohms, and trace that line until you find your short circuit.

Lewis

From rectifier cathode to chassis is 1100ohms
From one field coil lead to chassis while connected is 1100ohms, the other is zero ohms. The zero ohm lead connects to the positive filter cap 38 and also to the 70k resistor number 45 on the schematic. The schematic doesnt specify which end is positive and negative on the filter caps, but the 2 negative leads of the filter caps meet at a terminal, then the positive of 37 goes to the rectifier, and the positive of 38 goes to 70k resistor #45&42, and eventually audio tube and output tube if you look at the schematic. Do these positive and negative leads sound like they are oriented correctly on filter caps?
Mike

Mike

This must be the circuit you are using?

http://www.nostalgiaair.org/PagesByModel/877/M0013877.pdf

Negative of 37 & 38 connect together to center tap of the high voltage winding of power transformer. You have these right.

The problem comes when you read from field and #38 positive to chassis there is zero ohms. This is a short. You can isolate the short by seperating components on this side. Any solder shorts?

Norm

:From rectifier cathode to chassis is 1100ohms
:From one field coil lead to chassis while connected is 1100ohms, the other is zero ohms. The zero ohm lead connects to the positive filter cap 38 and also to the 70k resistor number 45 on the schematic. The schematic doesnt specify which end is positive and negative on the filter caps, but the 2 negative leads of the filter caps meet at a terminal, then the positive of 37 goes to the rectifier, and the positive of 38 goes to 70k resistor #45&42, and eventually audio tube and output tube if you look at the schematic. Do these positive and negative leads sound like they are oriented correctly on filter caps?
:Mike

Ok, I isolated the short (I think) to the wire that goes from 38 to the output tube plate (42 tube). I'll try to disconnect whatever else is connected to the same pin to see if it another connected wire that is the short or if it is at the plate.
Mike

It works!!
I traced the short from that pin on the 42 tube to a small coil (#20) that is mounted to the inside of the chassis, and has a metal tab that was pushed into the chassis thus shorting it. Thanks Norm and Lewis for all the help. Hopefully next time It will be a bit easier to identify and find a short.
Mike

:It works!!
:I traced the short from that pin on the 42 tube to a small coil (#20) that is mounted to the inside of the chassis, and has a metal tab that was pushed into the chassis thus shorting it. Thanks Norm and Lewis for all the help. Hopefully next time It will be a bit easier to identify and find a short.
:Mike

Congrats on a good job. We just gave you a little advice, you are the one that found the short.
Lewis