Hi folks

I have an old valve radio that makes a "cracking" noise now and again. I'm not sure if theres a problem with the radio or a reception issue? how can I tell the difference?

Thanks

Simple.

1. Turn the volume to zero. Does it still happen?
2. If not, short the antenna and earth terminals. Does it still happen?
3. If not, it's interference. See below.

If the noise still happens with either (1.) or (2.) it's in the radio.

If (1.) it's after the volume control, if (2.) it's before.

Sounds like silver migration. Look for a mica cap that's connected from anode to ground anywhere. I had an AWA battery valve radio that would make the most alarming and loud "crack!" periodically and that's what it was.

If the radio has a first generation 6M5 with the flat button glass base on it, these suffered from silver migration across the glass between G2 and G1 pins which, on the 6M5, are adjacent. You can actually scrape the silver off the glass for a temporary repair.

Noise from an arcing thermostat in a fridge can enter through the mains wiring, especially if the radio still has 2 core flex (which should be replaced and the chassis grounded).

I'll leave it to others to bang on about replacing all the paper caps and the electros. That's not what's causing this fault, but we all know it should be done if not already.

A more permanent answer to 6M5 and Silver is to dip its bottom in Hydrochloric Acid. Do not forget the tracking metal can get onto the socket and it may need cleaning. I have had a loose dirty pin issue with a 6M5:Simiar effect.

There is that much RFI on AM its beyond a joke.

Do take note at to what is turning on and off around you.

Frequencyman: Is related to your previous thread?

https://vintage-radio.com.au/default.asp?f=1&th=2059

Going back to that link. I have a Honda inverter/ generator. Despite any claims made it is totally unsuited to run a valve radio.

Spends more time running 240V power saws off grid, or the refrigerators during power outages.

On the odd occasion where a Mica cap fails, its fail mode is usually "snapping", "crackling", or "popping" (do not add milk) That being similar to dirty tube pins, or ones with bad contact. Oxy welding "tip files" can savage dirt & corrosion in some sockets.

Use a Chopstick, or similar to probe wires & nodes to ensure there are no dry joints. I inspect then mark everyone & have often found missed nodes with issues (like pin 7 on a 6V6 that got out of the factory with no solder)

Marc

I have used the larger dental piksters dipped in contact cleaner to good effect on dirty octal sockets.