The man came to install my set top box, so I've now got 21 channels of food, murder, and advertising. Actually, the picture quality is quite good. I'd been told I'd need satellite, but I don't think I'll bother.

The question is this. I notice, when I mute the sound during the ads, I often get a raucous buzz rather than silence coming out of the Pye's speaker. It seems to have something to do with captions, because it doesn't happen with normal picture material. Is it harmonics from the video waveform of the lettering getting into the sound carrier? Is it "normal" with an old set like mine, or does it indicate a fault somewhere?

Hi Sue

What model Pye is it?

I'm curious as I used to fix TVs in another life and fixed my fair share of Pye

Regards
Marc

It's a 1968 Pye Pedigree 23" table set, model 501PA. It's one of the hybrid Pedigrees - oops, pun not intended!

The "buzz" in the sound with captions is a common issue with older TV's. I'd regard it normal behaviour since it is only occurring with captions.

I remember that when I used to watch telly on an old B&W set. If there were subtitles or other graphics like the footy scores written on the screen then there'd be a buzzing noise. From memory it would also happen with a lower intensity with still pictures too.

I suppose it's worse now because of all the electronic lettering they cram into adverts. Anyway, it's tolerable when the mute's off.

I recall a similar problem with B&W televisions, especially with some ads that had high contrast between black and white with lots of white, such as white sheets on a clothes line.

Out of curiosity, I Googled around and found these items on the subject:

Yup, it's called caption buzz. Basically what happens is the peak white level of the luminance information (which shows the white letters of the subs/captions) exceeds 100% modulation of the vision carrier and this spills over into the audio carrier, giving you the buzz noise.

Off memory it happens with cheap tuners, and those where the tuning frequency is slightly off. Also some models of TV are more prone to it than others.

Is your connection via RF or AV? If via RF, try disabling the AFT and slight retuning. If this does not work the vision demodulator coil or sound demodulator coil might require slight adjustment.

Also known as video or frame buzz, sometimes caused by the agc not working properly, which in turn is quite often because the agc filter cap is leaky, reducing the agc volts = too much gain and overdrive of the demod.

I think most sets had an agc preset pot that could be adjusted for best contrast without buzz.

Thanks for that. I'll look at the AGC. I know the tuner is dodgy, because a signal on channel 11 comes in on channel 10, and most of the channels above 5 are just on the edge of tuning. The low band channels are tunable, which I'd guess means that one of the capacitors which determines the oscillator frequency has drifted downwards in value. It's an Astor-made turret tuner, BTW.