CRT Television Hum

I have a analog TV that is still working fine and no plans to replace it. Over time, it has developed an audio hum - I'm guessing it's 60 Hz. When the picture is dark, the hum is nearly gone. The brighter the picture, the louder it is. I'm guessing some kind of filter on the speaker connections would do it, maybe something as simple as connecting a capacitor circuit.... But, as I ain't the sharpest feller with audio electronics, I thought I better ask the genius pool here!

First I thought was a power cord was near the antenna cable, but that doesn't seem to be the problem.

The key word in all this is "cheap". Anything over $10 is way out of line.

Snuffy

Probably the HV flyback power and the audio (sound amplifiers) power are taken from a common filter capacitor, which has developed high internal resistance. If you can replace or bypass (put an auxiliary capacitor in parallel with the weak one), that should fix it.

The hum is caused by voltage droop when the screen is lit, modulated at 60 Hz because the screen blanks for a while during vertical retrace.

On Tuesday, July 7, 2015 at 3:02:29 PM UTC-4, Snuffy Hub Cap McKinney wrote :

Over time, it has developed an audio hum - I'm guessing it's 60 Hz. Whe n the picture is dark, the hum is nearly gone. The brighter the picture, t he louder it is. I'm guessing some kind of filter on the speaker connectio ns would do it, maybe something as simple as connecting a capacitor circuit .... But, as I ain't the sharpest feller with audio electronics, I thought I better ask the genius pool here!

sn't seem to be the problem.

e.

Are you sure it's coming from the speaker? Deflection yokes are known to h um as the mastic snot that locates the convergence shunts dry up from age.

it. Over time, it has developed an audio hum - I'm guessing it's 60 Hz. When the picture is dark, the hum is nearly gone. The brighter the picture, the louder it is. I'm guessing some kind of filter on the speaker connections would do it, maybe something as simple as connecting a capacitor circuit.... But, as I ain't the sharpest feller with audio electronics, I thought I better ask the genius pool here!

doesn't seem to be the problem.

line.

- Are you sure it's coming from the speaker? Deflection yokes are known to hum as the mastic snot that locates the convergence shunts dry up from age.

Yes, the hum goes up and down with the volume.

replace it. Over time, it has developed an audio hum - I'm guessing it's 60 Hz. When the picture is dark, the hum is nearly gone.

are

internal resistance.

with the weak one),

at 60 Hz

Thanks, whit3rd. I would give it a try but unfortunatley for me, I don't have a schematic and not up on TV circuits.

Not related to this... but have been meaning to ask.... I would like to pick up radio stations AM & FM that have weak signals. Is there a home-brew antenna method I can use for this? Like the TV, if there's something relatively simple and low cost I'd like to try it. Not worth more than a few dollars.

The fact that the hum amplitude changes with brightness, does suggest to me that the original suggestion is correct. I've heard this sort of brightness-varying hum from older TVs in the past, and it was definitely coming from the speakers. TVs are tough places for capacitors due to the internal heat... so, a dried-up filter cap is a good suspect.

A lot of "60 Hz" hum or buzz from televisions actually has a lot of harmonic content - it's a long way from being a pure sinewave. A simple high-pass or notch filter to take out the 60 Hz won't be very effective in getting rid of the nuisance.

If you are receiving an analog signal (either from a transmitter or from a digital converter box) then you may just need to re-check the tuning to get rid of the hum.

For each channel, the video and sound signals are transmitted on nearby frequencies, and if the tuning is slightly off, the video signal can get into the sound receiver, causing a buzz that changes with the picture content.

If re-tuning doesn't fix it, maybe you can borrow an ESR meter and check for any dried up capacitors that might be resulting in ripple on a power supply rail, though I think this is unlikely to affect the sound without also affecting the picture.

Chris

Not only that but it is more likely 120 Hz hum.

I would go with loose frame-deflection yoke coil, wash over with traditional copal varnish and allow to dry.

t. Over time, it has developed an audio hum - I'm guessing it's 60 Hz. W hen the picture is dark, the hum is nearly gone. The brighter the picture, the louder it is. I'm guessing some kind of filter on the speaker connect ions would do it, maybe something as simple as connecting a capacitor circu it.... But, as I ain't the sharpest feller with audio electronics, I though t I better ask the genius pool here!

oesn't seem to be the problem.

ine.

Although a common problem, OP responded that the noise tracks with the volu me, so that leaves out mechanical considerations.

AGC problems can cause video to bleed over into the audio circuits.

Mark Z.

Over time, it has developed an audio hum - I'm guessing it's 60 Hz. Whe n the picture is dark, the hum is nearly gone. The brighter the picture, t he louder it is.

If you are tuning analog signals on VHF/UHF recheck the fine tuning, the tu ner could have drifted slighty over time. If it has AFC try to disable that and fine tune manually.

The cheap scart plugs common around here tend to make poor contact and caus e these problems. Usually the problem is fixed by reseating the plug. Eithe r the pins develop some type of corrosion or contact resistance or the smal l wires that are pressure pressed inside the plug are not very well pressed .

"Snuffy "Hub Cap" McKinney" wrote in message news: snipped-for-privacy@earthlink.com... I have a analog TV that is still working fine and no plans to replace it. Over time, it has developed an audio hum - I'm guessing it's 60 Hz. When the picture is dark, the hum is nearly gone. The brighter the picture, the louder it is. I'm guessing some kind of filter on the speaker connections would do it, maybe something as simple as connecting a capacitor circuit.... But, as I ain't the sharpest feller with audio electronics, I thought I better ask the genius pool here!

First I thought was a power cord was near the antenna cable, but that doesn't seem to be the problem.

The key word in all this is "cheap". Anything over $10 is way out of line.

Snuffy

===

Thanks for all the good info. If I had a place to work, I would take a look, but the most practical for this one is to get a replacement set, new or used.

I use a CRT monitor on one of the computers here and LCD displays can't compare with his colors. But the power cost is definitely higher -- plus, more importantly during the summer - it heats up the room...

"Snuffy "Hub Cap" McKinney" wrote in message news: snipped-for-privacy@earthlink.com...

Look on Facebook or Craigs list for a free TV. They are always giving those old things away. The power cord could be wrapped around the antenna and not cause hum. Probably a filter capacitor needs replacing. If you had some on hand, open the TV up and just hold the leads of the new one across the capacitors and find the one where the hum quits .

CRTs are better as they generate the required light only, unlike LCD where the backlight is always full on no matter the screen contents. This is an a dvantage as far as efficiency goes. Also LCD require more digital processin g. At the end the energy wasted to run both is similar, just look at the ra ted power consumption, you may be surprised. 28" CRT TVs take 100W typ. whi le similar size LCD are rated 130W typ.

CRTs are better as far as efficiency goes in they generate the required lig ht only, unlike LCD where the backlight is always full on no matter the scr een contents. Also LCD require more digital processing. At the end the ener gy wasted to run both is similar, just look at the rated power consumption, you may be surprised. 28" CRT TVs take 100W typ. while similar size LCD ar e rated 130W typ.

CRTs are better as far as efficiency goes in they generate the required lig ht only, unlike LCD where the backlight is always full on no matter the scr een contents. Also LCD require more digital processing. At the end the ener gy wasted to run both is similar, just look at the rated power consumption, you may be surprised. 28" CRT TVs take 100W typ. while similar size LCD ar e rated 130W typ.

Though I guess at least 2/3 of the electron beam power in a CRT would go into heating the shadow mask or aperture grille. (Unless it is a black and white set.)

As well as the picture content, I guess in LCD TVs they lose a lot of light in the polarisers, on top of what is lost in the R,G,B filters.

You make a good point, some CRT TVs are quite efficient. Also I like the idea of having a particle accelerator in the living room.

You've probably got one in the kitchen, too!