10-15-2022, 05:13 PM
Recently finished repairing a Philco 84b. Had to replace all the capacitors, resistors, and wiring as it was all in pretty bad shape. Surprisingly, all the coils testing good and no signs of the green disease typical of these units. The first time I powered it on, it gave an instantaneous humming. Tracked that down to a poor ground connection on the #6 pin on the 77 tube for the 2nd IF and fixed it with a short jumper wire soldered to the chassis.
Now, I'm having a heck of a time with a very weak volume control. I can tune in a few stations, but get a really weak volume. When I hover my hand over or touch the cap on the 1st Det/Osc tube, the volume jumps right up. Same thing happens when I touch a metal probe to the #1 and #2 tabs on the bottom of the antenna coil (one coming in from the volume control, the other going out to the tuning condenser). Pulled the antenna coil a second time to double check for continuity and measure the resistance. Measured 3.0 and 6.4 ohms respectively. Went back through and double checked solder connections and looked for any inadvertent groundings taking place and didn't find any issues.
At this point, I'm completely baffled. Any help would be greatly appreciated.
Attached are the schematics and a link to short video showing the issue.
https://www.youtube.com/watch?v=aR-IPtOLr88
Now, I'm having a heck of a time with a very weak volume control. I can tune in a few stations, but get a really weak volume. When I hover my hand over or touch the cap on the 1st Det/Osc tube, the volume jumps right up. Same thing happens when I touch a metal probe to the #1 and #2 tabs on the bottom of the antenna coil (one coming in from the volume control, the other going out to the tuning condenser). Pulled the antenna coil a second time to double check for continuity and measure the resistance. Measured 3.0 and 6.4 ohms respectively. Went back through and double checked solder connections and looked for any inadvertent groundings taking place and didn't find any issues.
At this point, I'm completely baffled. Any help would be greatly appreciated.
Attached are the schematics and a link to short video showing the issue.
https://www.youtube.com/watch?v=aR-IPtOLr88