[mancave]

I've recapped a 51-530 and replaced several out of tolerance resistors. It plays ok, but there is a popping sound between stations. It mostly disappears when a strong station is tuned in. I cleaned the tube sockets, particularly the two loctals, and that seemed to help somewhat. Question: can a Philco of this vintage have SMD? Other things to look at?

[radiorich]

Hello mancave,
to answer your question yes that model does have those dreaded IF cans.

Sincerely Richard

[RodB]

I've had luck taking them out of the can, removing the mica caps from the circuit by lifting the spring loaded contact to each cap then solder in a 50-60pf cap to each winding. You have nothing to lose and it's not too difficult if you're careful and mark your trail. Pay attention to the position of the transformer primary and secondary inside the can and how it's mounted on the chassis.

[Arran]

I would suggest leaving the IF cans alone until you rule out all other faults, those are very delicate on the inside with hair thin wires, popping between stations sounds like some form of interference. Are there any electric fences in your area? Can you pick up the popping on any other radio? There is also a capacitor across the power line in these sets, if that's open you will get all kinds of noise.
Regards
Arran

[mancave]

I'll try the radio in a different location to see if interference is a factor. I did replace all capacitors, but I'll check the across the line cap to make sure it's not open. I'm not eager to open the IF cans! Thanks.

[morzh]

Also see if tuning cap is dirty and might need cleaning.

[MrFixr55]

To elaborate on Arran's comments: Try running 2 similar radios in the same location, in the same outlet. If it happens on both radios, then the issue is likely external, but could be power transformer arcing (that would likely transmit to the other radio, however, your radio does not have a power transformer). If only in the radio in question, it is internal.

Yes, the lack of power line filter caps can allow external interference in. early (late 1929s) AC radios did not have these. I could pick up the oven heating elements cycling on my Radiola 16.

If external, s the popping occasional or frequent? Do you have an electric stove or electric water heater?

SMD or any arcing in the radio can cause this. As Arran pointed out, a dirty tuning cap can also cause this. This most commonly presents itself as noise as the tuning knob is rotated, and is more likely to occur the more the plates mesh. If you turn the radio to the highest frequency (tuning cap completely open) and the noise goes away, the issue is in the cap. If the noise still exists, it is elsewhere.

The noise may be further isolated by removing the 2nd IF tube (on your set, you will need to bridge the filament connections with the appropriate 40 Ohm 5W resistor, or bridge and pray. If the noise disappears or is greatly reduced, the issue is not in the audio section.

Did you replace all the caps? Maybe replace the resistors. Swap the tubes. If no joy, you may be looking at SMD.

[Ron Ramirez]

FWIW, any 1950s AM radio I ever observed with SMD exhibited a thunderstorm-like constant static, not just "popping". So I wonder if this is just the beginning of SMD, or possibly an external source of interference?

[Chas]

or possibly an external source of interference?

If a cell phone is nearby RF "popping" comes from a battery maintenance circuit. This noise extends down into audio and can be picked-up on wired computer speakers.

If the phone is completely off, this does not occur...