Old Grundig Valve Radio Sound Problem

[octavez]

Hi,

I got an old Grundig Valve Radio, KS560: http://www.radiomuseum.org/r/grundig_ks560_1.html

It is working well but since few days the sounds start pumping like a heart and it sounds really bad. I'm guessing that it's a valve which is probably dead but since there are 8 tubes in it I'd like to know if there is a way to isolate it. I have almost no knowledge in this domain!

Thank you!

 

[shrtrnd]

Do you know anybody with a tube tester?

 

[KJ6EAD]

You could be experiencing a condition known as "motorboating". Look it up on Google or in the Radio Museum. It can be caused by something as simple as a leaky bypass capacitor allowing RF into an audio amplifier stage.

 

[duke37]

Motor boating is almost certainly due to bad capacitors. I would go for the HT bypass smoother capacitors. You could get a 10uF or so capacitor and temporarily connect this across the bypass capacitors to find the faulty one(s).

Don't kill yourself!

 

[octavez]

Thank you really much! I'll investigate it!