Low volume

[andrefranc]

I checked the ceramic resistor in circuit and no opens. Should I disconnect it to check or is in circuit good enough? I was told that between 2 and 3 it should be 2450 ohms and I only have 180 ohms there. How do I know what it should be? One 24 has a plate voltage of 273, 1st tube, and the next one only has a plate of 103 volts. Can't see why though. I replaced the caps inn the power supply with electrolytics, 10's, but the cap across the choke I left as is, would it be the problem?

[radio63]

I'll have to see if I still have data on what the voltages/resistance of each section should be, but yes, you should check each section with at least one lead disconnected from the circuit. Otherwise you might have erroneous readings.

I do believe the 24s have different plate voltages in that set. I'll have to look up my notes. It has been many years since I worked on my set. The cap across the choke could be a problem, but I would check the resistance in the power resistor first.

Gilbert

[jeyurkon]

Originally Posted by andrefranc

I checked the ceramic resistor in circuit and no opens. Should I disconnect it to check or is in circuit good enough? I was told that between 2 and 3 it should be 2450 ohms and I only have 180 ohms there. How do I know what it should be? One 24 has a plate voltage of 273, 1st tube, and the next one only has a plate of 103 volts. Can't see why though. I replaced the caps inn the power supply with electrolytics, 10's, but the cap across the choke I left as is, would it be the problem?

The schematic on nostalgiaair shows that it should be 187 ohms between 2-3. It would be 2470 between 5-6. Your reading seems correct. The plate voltages are off a bit, but not unreasonably so, in my opinion. The schematic gives conflicting information here. In a table it shows they should both be 250V but on the schematic it shows 225V for the first 24 and 130V for the second 24. And as was noted by Reece the table shows 215V for the 71's but 190V on the schematic.

Knowing the readings for the other tubes might help.

John

[radio63]

The data on Nostalgia Air is very helpful if you don't have a hard copy of the schematic in front of you. However, I would measure the resistance as I had mentioned earlier, by disconnecting one of the leads of each section from the circuit.

Here's some additional info from my notes of 20 some odd years back, voltages I measured at the resistor. These are approximate, and just to give you an idea what another Model 20 once measured. The resistor has 7 terminals with number 1 toward the front of the chassis. Voltages were measured to the chassis if I recall correctly.

terminal 1 +50 volts (varies with volume control)
terminal 2 -6.8 volts
terminal 3 chassis ground
terminal 4 +2.4 volts
terminal 5 +12 volts
terminal 6 +92 volts
terminal 7 +120 volts

Again please remember these voltages are approximate, but if you measure something very different from the above voltages, it might be an indication of possible trouble. I worked on this set in 1985, so it's been a long time but this is what I have in my notes. Another trouble spot on these early Philco sets are coils that corrode and open. That may be another thing you wish to check out. Good luck and let us know how it goes.

Gilbert