Zenith J615 - Poor reception; Distorted sound

Bill:

I have replaced all the paper caps and the electrolytics. This is an AM set with two IF cans. I cleaned them both.

I am going to replace six or seven resistors that are testing about 20% too high and then align the radio. I have two other identical Zenith J615 radios, so I will try swapping out some of the tubes in the event that I have a bad one in this set.

Hopefully these measures will help with the sensitivity and distortion.

Thanks!
Dick

That isn't likely your problem. That is normal percentage. Many resistors were originally rated that high.
Perhaps poor connections, or and intermittent cracked resistor?
Bill Cahill

For the heck of it, I took a small transistor radio and plugged it into the RCA jack on the back of the old Zenith. While the volume level was rather low even with both sets volume levels at max, the sound out of the Zenith was very clear, with no static or distortion.

Does this tell us anything?

Yes. Radio section is at fault. Probably bad I F's.
Something isn't right there.
Maybe a bad mica cap elsewhere?
Bill Cahill

Just plain sounds like silver mica problems in I F transformers to me.
Bill Cahill

In other words if you get a clean signal though the audio input jacks, that eliminates problems with the audio section, and makes either the RF or IF section the areas to troubleshoot. Just as Bill had stated.

Well then, I received replacement IF cans today. I guess I'll replace the ones I cleaned, align it, and see what that does. I'll check on the mica caps, too.

Thanks for the help!

That chassis also has a couplet in the audio section. Though it is believed on this board and others that couplets "never" fail, I have two Zenith radios with the 6J05 chassis that have indeed had bad couplets. One gave symptoms much like "silver mica" disease and the other caused distorted and weak output. The coupling cap from the 12AV6 first audio tube to the 50C5 output tube is in that couplet. BTW, you just proved my contention that silver mica disease is a figment of someone's imagination. You went thru all the trouble to "fix" the silver mica problem, and you still have it!

Good luck

Chuck

I don't know whom here gave that opinion. I, for one, have occasionally had coupltes go bad.
Usually, distortion, occasionally, just very low volume.
Once in awhile, some background static. It's easy enough to find out if it's the amplifier. Disconnect Det. from ausdio amp. If it has a phono jack, switch it to phono.
Bill Cahill

Now that we agree about couplets......Am I missing something or have we been working without a schematic, without any resistance or voltage measurements. Have we disconnected the circuit after the second IF to see if the noise was in the IF or after it? There is no phono input, so it has to be done the hard way, with a signal tracer on the output of the IF. Others have suggested systematic diagnostic procedures, but I guess we are going to try a fix this radio by just throwing parts at it and see what sticks. There is also weak output with distortion. Silver mica disease has nothing to do with that. There needs to be real diagnostics done with real diagnostic equipment using a schematic, not wishful thinking and guessing.