Slowly putting a Philco 48-482 radio back together.
Question on using as is, or replacing three Dogbone Capacitors which measure uniformly below their marked values (all three are marked 470 pF +/- 20%). Schematic shows them to be 510 pF, though again physically are marked as 470 pF. Two serve as RF Bypass, and one is listed as Oscillator Plate Feedback. The two for RF bypass measure C506 = 341.3 pF, C507 = 389 pF. The one described as Osc Plate Feedback measures C517 = 367 pF. Photo of C506 is attached as is a photo the segment of the schematic (sorry it is sideways).
Seems like since the original schematic shows 510pF and the factory, I assume, compromised with 470pF, perhaps because they were more cost effective at the time (?), that the drift down to the 3xx pF range is already straying well away from the original design, it might be worth considering replacement. That said, if the receiver appears to perform well as is, I wouldn’t touch them. Replacing caps in the tuning or IF section of a receiver will at the very least require a complete re-alignment, though I’m guessing you’re probably planning to do that anyway.
All-in-all, if they work well, I’d say let sleeping dog-bones lie.
Agreed I would leave them. The chances of them being bad are very low. What are you using to measure them? Test leads and poor calibration could easily cause the difference you see which is common in the pico range. Depends on what the tolerance is because that is within 10 percent but I would expect an oscillator circuit to have tighter tolerance. Tube stuff is pretty forgiving with tolerance so I wouldn’t stress if everything wasn’t right at spec. Get it together and see how it performs then go from there.
Radios + Tubes + Scopes + Cars= Nothing better!