The PHILCO Phorum

I'm fairly new at this so please bear with me. I do have a basic understanding of tube radio circuits (I've been helped greatly by a studying a copy of Elements of Radio Servicing by William Marcus -- highly recommended.)

I replaced all of the electrolytic and paper caps and checked all the resistors. Injecting a modulated 455 hz signal at the IF stage gives a good output on the speaker. However, the same signal at the input of the mixer gives a softer tone from the speaker. Tuning the radio to about 600 hz and moving the tuning dial on the signal generator doesn't give any tone when rotated through 600 hz. I'm suspecting that the oscillator is not running. The schematic calls for 110 volts (phono) 45 volts (radio) at the grid of the 7C5 oscillator. I get 118 and 47 respectively with my multi-meter. Since the original readings were with a 1000 ohm per volt meter I suspect my slightly higher readings are ok. However, the voltages at the plate should be 220 volts (phono) and 83 volts (radio) but I get 233 (phono) and 168 (radio). That last one seems too high. I did find a 15,000 ohm resistor (buried under all the wiring for the pushbuttons) that is in the plate circuit that I had missed before. It measures 21,000 ohms in circuit so I replaced it with a 15,000 ohm resistor. No help.

My problem is that I'm not able to understand the oscillator circuit since all the pushbutton switches and wiring is confusing me. The schematic shows the all pushbuttons in the "out" position but when I'm trying to test the radio I have the "broadcast" button pushed in. I don't understand what the schematic should look like with a button pushed in.

Any help understanding the effects on the circuit with the button in or any advice on what to check next would be greatly appreciated.

Pleae post link to schematic so we can browse it along with you. Often these sets had presets which were tuned for stations, and one that allowed manual tuning. These switches need be cleaned out and move freely to make proper contact. I like Deoxit. You need to make sure you are using the manual tuning selection whilst doing alignment.

Link to schematic on nostalgia air: http://www.nostalgiaair.org/PagesByModel...013494.pdf

Agree with CF. With you want the hear the osc running tune the Philco to 1000Kc. Use a small transistor radio and hold it near the osc coil or the 7C5 osc tube. The osc is going to be running 455Kc above the incoming signal which means to tune the transistor set to 1455kc or so. If it is working you will hear the signal in the xsistor set. Will sound a loud hiss or squeal.
Terry

Ok, had some time last night to work on this again and gave the pushbutton assembly (and the other controls) a good cleaning with a good electronic contact cleaner. Now it picks up lots of short wave stations with good volume. The broadcast band, however, now picks up a couple of stations but I have to have the volume at max to hear them. This brings up another question I have: what IF frequency does the short wave use? The schematic says 455 kc for "standard" and 4.5 mc for FM but doesn't indicate anything for short wave.

It's 455Kc same as the BC band.
Terry