01-02-2008, 11:47 PM
Hi JT
Assuming you have the 118 schematic...
Condensers (74) and the 8 uF section of (73) are the main filters in the radio. The positive leads of each connect to either side of choke (71). with a 0.25 uF condenser, (72), connected in parallel with the choke (71). The negative leads of the two 8 uF condensers connect to B-.
There is also a 10 uF, 25 volt section to condenser (73). Its negative lead connects to B-, and its positive lead connects to ground.
Your voltage readings will be somewhat higher for two reasons:
1. Today's line voltage is higher than it was 73 years ago; and
2. Modern multimeters are much more sensitive than the standard of 73 years ago, which was 1000 ohms/volt sensitivity. Those older voltmeters tended to load down the circuit under test, making the readings then appear to be lower than they actually were.
Now if your plate voltages are significantly higher than those in the Philco voltage chart, then you need to look for a problem.
Another point. There are four more electrolytic condensers used in Model 118, the four-section can (46). It contains three 1 uF sections and one 2 uF section. In this can, all four negatives connect to chassis ground so no confusion there. If you have not replaced this can...do so. This could very well be another source of hum. Other problems include (but are not limited to) heater to cathode shorts in tubes, defective field coil and/or filter choke, and defective condenser (72).
ALL electrolytic AND paper condensers need to be replaced, for reliability and safety.
Assuming you have the 118 schematic...
Condensers (74) and the 8 uF section of (73) are the main filters in the radio. The positive leads of each connect to either side of choke (71). with a 0.25 uF condenser, (72), connected in parallel with the choke (71). The negative leads of the two 8 uF condensers connect to B-.
There is also a 10 uF, 25 volt section to condenser (73). Its negative lead connects to B-, and its positive lead connects to ground.
Your voltage readings will be somewhat higher for two reasons:
1. Today's line voltage is higher than it was 73 years ago; and
2. Modern multimeters are much more sensitive than the standard of 73 years ago, which was 1000 ohms/volt sensitivity. Those older voltmeters tended to load down the circuit under test, making the readings then appear to be lower than they actually were.
Now if your plate voltages are significantly higher than those in the Philco voltage chart, then you need to look for a problem.
Another point. There are four more electrolytic condensers used in Model 118, the four-section can (46). It contains three 1 uF sections and one 2 uF section. In this can, all four negatives connect to chassis ground so no confusion there. If you have not replaced this can...do so. This could very well be another source of hum. Other problems include (but are not limited to) heater to cathode shorts in tubes, defective field coil and/or filter choke, and defective condenser (72).
ALL electrolytic AND paper condensers need to be replaced, for reliability and safety.
--
Ron Ramirez
Ferdinand IN
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