Hi this Philco is running low B+ all around, I am getting about 60 volts to the plates that require 95 volts. The filters have been replaced and the rectifier test good. One thing I have noticed is that the speaker field coil is dropping about 45 volts, this seems high to me, and it's dc resistance is about 500 ohms. I can get some noise out of the speaker when I touch the grids of the output tube and the detector tube. Any Ideas?

:Hi this Philco is running low B+ all around, I am getting about 60 volts to the plates that require 95 volts. The filters have been replaced and the rectifier test good. One thing I have noticed is that the speaker field coil is dropping about 45 volts, this seems high to me, and it's dc resistance is about 500 ohms. I can get some noise out of the speaker when I touch the grids of the output tube and the detector tube. Any Ideas?

Hi Kris,
Where are you connecting the negative lead of your voltmeter? The schematic I'm looking at shows B- is not the chassis on this radio but is floating above it. B- can be found at the negative leads of the power caps. Hearing noise when touching the grids is a good thing. Suggests the problem is at the front end somewhere. Possibly antenna connection, oscillator not running, or IF stage.

Richard

Thanks for the reply, I am measuring from the negative end of the filter caps.

Hi Kris

Since this is an AC/DC radio 45 volts dropped across the field is a lot. Check for leaky caps. If #24 (pin #5 of 50L6) is leaky your 50L6 will draw too much current. If #30 is leaky voltage will also be lost. Here is a schematic:

http://www.nostalgiaair.org/PagesByModel/512/M0013512.pdf

Norm

:Thanks for the reply, I am measuring from the negative end of the filter caps.

Hi, all of the wax caps have been replaced including the ones you mentioned, but the B+ is still low.

Hi Kris

Measure between pins #5 and #8 on your 50L6. Pin #5 should be 5 volts or more Negative. If it's not the tube will draw too much current. Tube could be gassy or grid resistor open?

You mention having around 65 volts B+ with 45 across the field. At the rectifier cathode this would give around 110 volts. If so the rectifier is ok.

Norm

:Hi, all of the wax caps have been replaced including the ones you mentioned, but the B+ is still low.

Hi, I got -3.5 volts between pins 5 and 8, the 50l6 was a little gassy so I replace it and the B+ increced to about 67 volts, better but it still dosen't work.

Is this radio working? Does it produce stations and music? If not, also check to see that there aren't any shorts in the IF transformer trimmer condensers (not likely, but it does happen on occasion) and also that there aren't any shorts between IF coils.

Have you checked all voltages in the radio? Are there any stages that are particularily low? You may try disconnecting various parts of the radio from B+ if you cannot locate any trouble otherwise. Of course if you disconnect the output tube from B+ there will be a very large increase in available voltage, but other sections are somewhat less likely to cause a huge increase unless they are troubled. The oscillator and other RF tubes will, however, have a higher current drain than the 1st audio tube.

Also remember that not all bakelite housed condensers use mica as their di-electric (insulator). Some of these units are actually paper condensers in disguise (if you can call it that). Bakelite housed condensers can often be found in the tone control circuits of the audio section as well as various parts of the RF section. As a tone condenser, these condensers are often connected with one side to B+ and one to B-, so this can load things down.

Thomas