sound buzz

[radio nut]

Once again my Muntz is giving me fits. I thought I was totally done with this set but it has other ideas.......
Turn it on and the sound is great......give it about an hour and it slowly starts buzzing through the speaker.......
text on the screen is worse.
The discriminator coil is a replacement from moyer's. All out of tolerance resistors have been replaced, and ALL of the caps in the sound circuit are new.
Although ceramic have been put in for bad micas.
Once warmed up well the buzz starts as soon as the dvd player I use gets turned on..
Any ideas?
Also This set does not have any power cord to ground interference caps.

[radio nut]

Also can a tube cause this kind of problem?

[radio nut]

One other thought.....The ratio detector coil I put in from moyers is of course new old stock.
It has 2 -5 picofarad caps in it. could those be the cause?
When I first installed it the sound was clean. And at that time was fighting other issues and have started putting many hours on this set.

[Kevin Kuehn]

You say you replaced mica with ceramic? Well ceramic caps can drift with temp, and discriminator circuits are pretty sensitive to drift. Hard to say without analyzing the circuit, but it sounds like a bad combination.

[Electronic M]

Could be the DVD player is producing RF noise at your sound IF frequency and messing with the audio.

[old_tv_nut]

Is there any change in the picture over this long period?
Does adjusting the fine tuning fix the buzz or at least change it?

[radio nut]

this muntz does not have fine tuning.....high end huh?

[dieseljeep]

Originally Posted by radio nut

this muntz does not have fine tuning.....high end huh?

One of Muntz's selling points was the fact, that once the set was set up in your home, it didn't need any adjustment, either by technician or user.
We all know how that worked out. They even had a set screw on the channel selector knob.

[wa2ise]

Originally Posted by dieseljeep

One of Muntz's selling points was the fact, that once the set was set up in your home, it didn't need any adjustment, either by technician or user.

That's probably because the set's video IF had a passband as wide as a barn door. So the local oscillator in the tuner drifting wouldn't matter. Taking full advantage of the FCC not placing TV stations in adjacent channels. It should look awful on analog cable.

[radio nut]

Well the sound IF coil was junk......tested dead on the primary. The sound still has a slight buzz but even a recalibration does not get it all out. BUT what buzz is present is tolerable and comes on as soon as the cheap dvd player is turned on. one of these days maybe I will get cable and see if its cleaner.

[earlyfilm]

Originally Posted by radio nut

. . . . what buzz is present is tolerable and comes on as soon as the cheap dvd player is turned on. one of these days maybe I will get cable and see if its cleaner.

Since your Muntz obviously is too old to have a video input, I assume that you are using some sort of a modulator.

Instead of feeding the TV directly, connect a rabbit ears to the TV and just let a 3 foot wire hang from one terminal of your modulator, with no direct connection of the set. This should lower the signal level enough to eliminate buzz from IF overload. It also will isolate the TV from your modulator in case the grounds are different.

And about cable, my newer box has no RF output !!!

James

[radio nut]

tried your tip and no go.....but I found that even with the dvd off and nothing hooked to the tv it has a buzz all the time. I wonder if I need a line interference filter for the power cord....?

[Electronic M]

In these parts there is still analog cable so I can just connect my sets straight to the wall(though I normally use a VCR as a tuner as the channels I most watch are not on VHF or UHF frequencies).

[wa2ise]

Originally Posted by radio nut

Turn it on and the sound is great......give it about an hour and it slowly starts buzzing through the speaker.......
text on the screen is worse.

I assume that the set is an intercarrier design. What usually happens to create such buzz is the video carrier momentarily disappearing when there is peak white in the video. Peak white corresponds to the lowest RF level in the modulated TV channel, and a misbiased or misaligned video IF stage going into cutoff killing the video carrier when the peak white happens. The video detector creates the 4.5MHz sound carrier by beating the sound carrier against the video carrier, and if that video carrier isn't there, you get no sound carrier into the 4.5MHz sound IF. These sound "holes" end up sounding like the buzz you're hearing.

I have a TV that suffers from this, but I cheated by reducing the amplitude of the video feeding the RF modulator. Leaving more RF amplitude when peak white happens.

[Kevin Kuehn]

The contrast control can emphasize this buzz too, if it's located before the sound pick off point.