Hi all, I have a Telaverta TV24 radio which has a strange fault. It works ok for a while then the volume slowly fades away. If I turn another radio on then off again the volume of the Telaverta suddenly shoots back up again. I have replace all caps and resistors and checked all the valves. Any ideas on what may be causing this? Could it be the micas in the IF cans?. Any help appreciated, Dave

Have you replaced the two 100pf mica caps, one of which go from the plate of the 6B6G to ground?The other runs between the plate of the 6U7G to one of the diode plates of the 6B6G and two 1 meg resistors. I'd try this before attacking the IF cans.

Hi Monochrome, I have replaced both these resistors and caps, another thing I noticed is that when I touch my meter lead on the wire from the 1st IF to the plate of the 6J8 the volume jumps up. All I have left to replace are the IF caps but I wanted to make sure there was nothing else that could cause this before I attack the IF cans. Any other ideas?

I spent months chasing a problem exactly like this.

I don't know your circuit.

Problem could be related to the feedback to the AGC coming from the volume control. Some slightly increased resistance in the volume pot or one of the components connected to it could be causing the "fade" as it warms up. Volume pots are often close to main transformer and rectifier, so they sometimes accumulate heat from there. AGC feedback often comes off a centre tap in the volume pot In my case that contact was worn, but a good clean and re-soldering of all associated joints fixed it. Because AGC is designed to respond dynamically to different incoming signal levels, a pop in the AC, as you describe, seems sometimes to cause AGC to recalibrate. Wierd, but that's my experience.

Maven

Well it looks like replacing the IF caps is out of the question, they are buried in pitch in the base of the IF trannie! Looks like it may be a quirk with this particular set, we must remember that all these electronic devices weren't plugged into the mains when these radio's were made. The problem is bad some days then almost non-existant on other days. May just have to put up with it!