Zenith K731 help
 

I have a Zenith K731 that has recently started losing some sound quality after playing for 10 or so minutes, before this, it played wonderfully. For the first 10 minutes, it sounds great, then the signal changes and becomes slightly clipped, losing the full frequency and introducing some distortion. It has been recapped and the selenium rectifier swapped out. I am assuming a tube is on its way out, but I don't have a tester. Anybody have any recommendations on where to start looking?

Could be a gassy output tube. You might also try cleaning the socket with Deoxit or some other good contact cleaner. A new tube will be the best test for the current one.

Also look for any paper caps and replace them. I had an RCA phono that showed the same symptoms. Cleared up with a recapping.

Good advice all: output tube going bad, bad caps in the audio circuit. Easiest is to try another tube. Another thing to look for is the cathode resistor on the output tube. It may have changed value and thus changed the bias on the tube. Measure ohms cold and compare to the color code on the resistor, should be within 20% if resistor is good.

Reece

Replace the coupling capacitor going to the G1 of the output tube, too.

Thanks for all the suggestions. I will give these a whirl and report back.

Yep. Bad output tube. All better now. Thanks for the help.

Now, I need to figure out why my Zenith M722 isn't picking up a station as well as it used to.