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 Post subject: Zenith TV Audio Buzz
PostPosted: Jan Thu 10, 2019 1:07 am 
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Location: Detroit, Michigan
Is my imagination, or do Zenith tv's seem to have a worse audio buzz problem than other makes? The type of buzz that changes pitch and intensity depending the video on the screen, but always present to some degree regardless of user control adjustment.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 10, 2019 3:25 am 
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Yes, their tube type sets were well known for that, and it was often complained about by customers. Particularly noticeable when there was writing on the screen or lots of white areas.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 10, 2019 3:41 am 
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Location: Albuquerque, NM 87123
You may have an alignment problem or a video source problem or both.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 10, 2019 3:53 pm 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 436
Location: New Hampshire
Yes that is a common fault & I am a big apologist for Zenith.
Usually in the olden days you could tame most of them by proper
adjustment of the quad coil, buzz control & AGC but that was with
a real OTA NTSC signal. With the new sources I would guess it may
be impossible in some cases.

73 Zeno 8)
LFOD !


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 10, 2019 7:08 pm 
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Joined: Jan Sat 16, 2016 10:03 pm
Posts: 383
I have many Zenith Portholes and yes it's most always a problem.

The problem is somewhere within the intercarrier Audio Circuit. I have realigned all of my sets and that has help a lot. Luckily Zenith produced an excellent service manual for these portholes so alignment was easy for someone like me.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 3:17 am 
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Location: Detroit, Michigan
Interesting. I have Zenith tv's from '58 to '71, and they all do this to one degree or another. Makes me wonder why, after it should have been apparent there was a problem, I think zenith knew it because all these sets have the buzz control, Zenith didn't dump this sound system design and go with something else. Was the buzz problem in the solid state sets after the tube era ended?


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 6:26 am 
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The problem is the quadrature detector. Some detector tubes work better than others. Generally the tube that was installed at the factory would work fairly well. But if you ever had to replace it, you would often have some buzz after installing the replacement tube. Adjusting the buzz control helps a little. I often wondered if there was some secret that TV manufactures knew and that the replacement tube manufactures did not know.

The quadrature detector was cheap. Any other type of detector worked better.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 2:07 pm 
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Tom Schulz wrote:
The problem is the quadrature detector. Some detector tubes work better than others. Generally the tube that was installed at the factory would work fairly well. But if you ever had to replace it, you would often have some buzz after installing the replacement tube. Adjusting the buzz control helps a little. I often wondered if there was some secret that TV manufactures knew and that the replacement tube manufactures did not know.

The quadrature detector was cheap. Any other type of detector worked better.


Hi Tom,

Is the quadrature detector you are referring to the FM limiter & detector 6BN6 tube in these ole portholes. I remember you gave me instructions a few moons ago on how to limit the buzz and I am still grateful for your time.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 4:15 pm 
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Location: New Hampshire
Kevin Clark wrote:
Interesting. I have Zenith tv's from '58 to '71, and they all do this to one degree or another. Makes me wonder why, after it should have been apparent there was a problem, I think zenith knew it because all these sets have the buzz control, Zenith didn't dump this sound system design and go with something else. Was the buzz problem in the solid state sets after the tube era ended?


Buzz was not a problem on SS sets. B&W sets seemed to suffer most, early colors the least. Why
they never did anything about it is beyond me. From at least the late 50's on they built the best tuner / IF
stages. Those sets could get stations no other sets could but they buzzed...........

73 Zeno 8)
LFOD !


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 5:21 pm 
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Location: Dallas, TX
The quadrature detector uses the fewest components. Maybe Zenith was the sole holder
of the patent and wanted to make the most of it. The design apparently has a problem
rejecting the 60 Hz video sync pulses.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 6:40 pm 
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Location: Ann Arbor, MI
clsoca wrote:
Is the quadrature detector you are referring to the FM limiter & detector 6BN6 tube in these ole portholes.

Yes, that is it.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 11, 2019 9:16 pm 
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Location: Detroit, Michigan
Wow, great info. I guess the first thing I'll do is try another tube in the set on the table, yep, it's a 6BN6. 1959 Model E2015L Ch: CH16D25Q, with the Space Command 300. This is the worst of the Zenith's I've had for the buzz, basically un-listenable.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Sat 12, 2019 3:24 am 
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You could try adjusting the buzz control and the quadrature coil. I assume you have a schematic and can locate the quadrature coil. Put a piece of tape on the alignment tool so as to form a flag. Before you start adjusting the coil carefully note the position of the flag. Then try turning the adjustment back and forth to see if you can reduce the buzz and get clear sound. If you don't get anywhere, return the adjustment back to it's original position.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Mon 14, 2019 1:45 am 
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Location: Detroit, Michigan
Thankyou, Tom. Great info.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Tue 15, 2019 2:28 am 
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Standard procedure on the Zenith tube sets that buzzed was to replace the 6BN6 (or 6Z10), adjust the buzz control for minimum buzz, and touch up the quad coil. Adjusting the IF transformers may help.

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 17, 2019 4:05 am 
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Location: Detroit, Michigan
Thanks, Tim, I've located the quadrature coil on the set. I have a few 6bn6's somewhere in the stash in the basement.


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Thu 17, 2019 4:44 am 
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Location: Ann Arbor, MI
It may be worthwhile to try the adjustments first. If the results are not good enough then try a different tube. You will have to readjust the buzz control after each tube change,

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Wed 23, 2019 3:57 am 
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Greetings to Kevin and the Forum:

I would suggest that you take a look at your signal source for proper modulation depth. Some sets may be more susceptible to sync buzz than others, but if the video modulation is limited properly, there should not be a problem.

Conversely, if the video modulation level is excessive, there will be no way to get rid of the sync buzz in the audio no matter what adjustments you make to the TV set.

The catch is that you need a precision demod and an NTSC waveform monitor to easily determine the video modulation depth. I suppose there are other methods, but I got very little sleep last night and no relatively simple way comes to mind.

If you want an explanation of intercarrier detection, let us know here and I am sure that I or someone else will detail it for you. Bottom line is that the buzz in the sound is a video problem, not an audio problem, although it can be exacerbated by incorrect detector alignment.

Good Luck,

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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 25, 2019 9:28 pm 
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Could one design and install a notch filter to suppress the intercarrier buzz?


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 Post subject: Re: Zenith TV Audio Buzz
PostPosted: Jan Fri 25, 2019 9:52 pm 
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Location: Ann Arbor, MI
cwmoser wrote:
Could one design and install a notch filter to suppress the intercarrier buzz?

No. The buzz contains a wide range of harmonics of the 60 Hz fundamental frequency. In fact it is mostly the harmonics that you hear.

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