Zenith J615 - Poor reception; Distorted sound

Hi All:

I'm an advanced beginner, if that makes sense, with a Zenith J615 Chassis 6J05. It was completely dead on arrival. I replaced all the electrolytics and paper caps. All tubes were checked and are good. The radio will now tune in a few stations, but weakly and with a fair amount of hum and static. The sound seems garbled or distorted as well. Any ideas which direction I should go from here?

(I actually bought three of these radios. The first one was a real mechanical mess, so I bought two more hoping I can get two good ones out of the three. The same issues described above relates to a second J615 I got working again. Maybe these particular radios weren't all that great to begin with in their day?)

Jack

Welcome to the forums.
May we see pictures? Do you have a schematic?
If this is a later set, including late 40's, they have issues with built in capacitors getting leakage in the I F's.
Also, Zenith tended to use alot of rubber wiring. Maybe that has gone south, and, is causing a short??
Sounds very possible.
You have sets playing. Now we need to help you locate, and, repair the problems.

Bill Cahill

Check resistors too, they can be out of tolorance.

I do have the schematic and I think I posted a couple pictures, but I'm not sure where they went.

The wiring seems ok. I have a feeling it may be the IF cans. Are they interchangable or can they be dismantled in order to replace the capacitors?

Regarding the resisitors, is it reliable to check them without unsoldering them? It would seem that if I go to the trouble of unsoldering them, I may as well just replace them as they are so inexpensive.

Thanks!
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Your problem is you are typing in the beginning, and, end of img.
If you are using something like photobucket, Point your cursor to the photo you wish to copy. A list should pop up.
The last one is the image code.
Left click on it several times to completely highlight the code. Then, right click on that code, and, select Copy.
Go to your post you are posting here, and, right click on blank spot. Select Paste.
That puts in the entire image code.
When you are finnished posting, and, tell the forum to send it, your pictures will show up in the post.
It's actually very easy.
Hope this helps.
Bill Cahill

Here are a couple pics.

Can I just swap out these IF cans for two NOS? Schematic says they are both 22 ohm and Zenith Part #s 95-1101 and 95-1102 or Merit Part #s BC-352 and BC-355.

Bill:

I followed your instructions and got the pics to appear. But they are Giant-sized! How would I attach a thumbnail?

Jack

This size is fine. Thumbnail is too small.
Your radio has the infamous I F transformers with the built in mica caps in the base. They often get silver mica disease. The only cure is to dismantle, clean, and, put back together the bases of the I F transformers. Other than that, have you replaced the selinium rectifier?
Have you tested the tubes?
Bill Cahill

Bill:

I did check the tubes and replaced two. I did not replace the selinium rectifier, but will look at that (to be honest - I wasn't aware of such a thing).

Regarding the IF cans, I read another thread on "Silver Mica Disease". That member had the same problem on the same Zenith radio and he choose to dismantle and remove the silver mica caps, replacing them with external caps. I think I'd prefer to just replace the cans. I found a source that has the Zenith and the Merit cans referenced in the schematic's part list, but I would rather use a Miller can that doesn't have the silver mica caps.

Is choosing a substitute Miller can as simple as getting an input and an output Miller 455kc can with the same number of lugs or is there other criteria to match up? The source has a slew of Miller cans.

I imagine that replacing the cans will necessitate an alignment, but I have a signal generator and will need to learn how to do this procedure - so this is as good a time to do that as any.

Thanks,
Jack

I checked my schematic, the chassis, and did a bit of research and have concluded that this Zenith model does not have a selenium rectifier. I believe that is accomplished with a 35W4 tube.

Jack

O.K. on rect. No, you can't go by just any I F transformer, You have to use a noted correct replacement, including in the Miller line. Use the correct replacement for each transformer. You could also install outside mica caps on the I F transformers you have, as long as you put in the correct valuess.
Yes, it will need realignment.
Bill Cahill

If i install mica caps on the exisiting cans, I would remove the silver mica caps integrated inside - yes?

That's correct.
Bill Cahill

I have ordered replacement IF cans, as per the specs. Meanwhile, I found a post by someone who took apart the existing IF cans and cleaned the silver mica caps. I tried that on both cans, found that there was definately silver mica disease, cleaned them up nicely and re-installed them.

The sound is improved with much less static. However the tuning sensitivity still isn't all that much better and the sound is still "garbled". Is it possible that I have a weak tube after all? I checked them all, albeit with an emmission tester - not a mutal conductance tester.

Thanks!

First, emission testers aren't that good. Could still be a bad tube. Have you replaced all the paper caps?
Did you do all the I F transformer repairs? How manny are in this set?
If it's an am, fm, there are likely 4. If you only did two, you also need to do the other two.
Bill Cahill

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.