New to valves, Dutch Philips TV with 50Hz speaker buzz

[Kyle__B]

I see. We're KPN fibre here, I wanted xs4all but not my decision. Maybe I should see where that aerial socket actually goes.

Parts have been ordered for replacing c503 in it's entirety, new valves too. Didn't lighten my wallet as badly as it could've done.

Been thinking about what turretslug said about the power supply and it's making me wonder if - for fun and not to fix anything - i could change it for a better design later on. The measurements on the diagram show +1 having 25v of ripple as normal which doesn't fit the way I think at all. I got into electrics through old computers, where a 1% dip is often the ragged edge of tolerable. I'm sure I could at least fit a bridge rectifier?

[Maarten]

KPN fibre isn't like traditional cable. It depends on from whom they bought the network and how much functionality they stripped but chances are there's no analogue FM on it. The TV signal might be either IPTV or DVB, again depending on how much functionality there was in the first place and how much they stripped.

"improving" the power supply could turn out to be quite a disaster. Ripple is also a means to reduce dissipation. You'll have several supply rails that are way too high without any visible or audible improvements to the sets performance. A bridge rectifier might do more harm than good. The set wasn't designed to have the chassis floating at negative mains instead of being tied to one side of the mains directly. You'd at least have to separate the valve heaters from the rest of the circuit and you might introduce hum or insulation breakdowns. It's reasonably hard to beat Philips designers on cleverness.

Please don't "revalve" the set as it won't help and might actually make the set less reliable and reduces its historical value. Valves are very low maintenance and should only replaced when worn (performance wise) or defective, with the possible exception of wanting to sell the set as "fully restored . You could try the PCL86 and PCL805, though, to see whether anything changes.

The only parts that should be considered routine maintenance are the paper capacitors. There is probably one more besides the X-rated ones you already replaced.

[AndiiT]

Hi, the audio amplifier circuit used in your television looks very similar to that used in the Philips AG 2126 record player, it may be worth looking at the circuit description for the amplifier as it is somewhat unconventional and is unusual in that no output transformer is required which is why the speaker impedance is quite high and also, I believe, critical to the correct operation of the circuit.

I may be able to copy the details I have and post them on here or send them to you via PM if that would help.

Regards

Andrew

[Nuvistor]

There is also a good article in Radio Constructor about this type of audio stage.
https://www.americanradiohistory.com...RC-1961-11.pdf

This article was written with the help of Mullard.

[Maarten]

I didn't really explain, but the reason I mentioned trying to swap the PCL86 and PCL805 is, that a heater-cathode leak could cause hum. For this syptom it isn't really needed to understand the circuit, though when trying to understand you'll surely appreciate its cleverness. This TV chassis is one of the last implementations of this circuit which was first used by Philips in some high end bi-ampli radio sets in the mid 1950's.

[Kyle__B]

Originally Posted by Maarten

KPN fibre isn't like traditional cable. It depends on from whom they bought the network and how much functionality they stripped but chances are there's no analogue FM on it. The TV signal might be either IPTV or DVB, again depending on how much functionality there was in the first place and how much they stripped.

The TV box are tiny black things on ethernet, I haven't really cared to mess with it. Only thing that I care is that the router they gave us is terrible.

Originally Posted by Maarten

"improving" the power supply could turn out to be quite a disaster. Ripple is also a means to reduce dissipation. You'll have several supply rails that are way too high without any visible or audible improvements to the sets performance. A bridge rectifier might do more harm than good. The set wasn't designed to have the chassis floating at negative mains instead of being tied to one side of the mains directly. You'd at least have to separate the valve heaters from the rest of the circuit and you might introduce hum or insulation breakdowns. It's reasonably hard to beat Philips designers on cleverness.

That's the kind of reply I'm trying to provoke. I'm no stranger to the inside of TVs but until now I've only worked on solid state stuff from the middle of the 80s at the oldest, particularly RGB monitors. There's obviously a lot of Don'ts when it comes to valve era stuff. If the ripple was a necessary feature was something I was wondering in particular. I did think about the heaters, being the only part that isn't fed by a diode.

Originally Posted by Maarten

Please don't "revalve" the set as it won't help and might actually make the set less reliable and reduces its historical value. Valves are very low maintenance and should only replaced when worn (performance wise) or defective, with the possible exception of wanting to sell the set as "fully restored . You could try the PCL86 and PCL805, though, to see whether anything changes.

I'm well aware, the only valves I've ordered are the 86 and two 805, just as a test. If they aren't the problem I'll refit the originals, if they're going to break they usually break quickly not after donkeys years.

The only other ones in there are laboratory of doctor Frankenstein looking things which are sitting where on a modern set I'd expect to find a nice sensible black plastic LOPT with a focus knob on it. Since they work fine and I have no idea how to disconnect them I'm leaving them well alone.

As far as originality and historical value I'm not concerned about that. Things change and are changed over time. Many live in 200 year old houses but very few of them decorate with arsenic wallpaper and live by candle light. Likewise if I live to see the day PCL805 is unobtainable, I'd rather modify it for a substitute than leave it as a broken museum artifact. The only thing that doesn't change anymore is the dead.

When I post about painting it pink and how to cut the bezel for fitting an LCD then you'll have the right to be concerned

The only parts that should be considered routine maintenance are the paper capacitors. There is probably one more besides the X-rated ones you already replaced.

Any guesses where it might be hiding? The X's were easy to find, showoffy faux gold things, haven't seen a third anywhere. I googled the maker and it turns out they're an audiofool thing now.

Originally Posted by AndiiT

Hi, the audio amplifier circuit used in your television looks very similar to that used in the Philips AG 2126 record player, it may be worth looking at the circuit description for the amplifier as it is somewhat unconventional and is unusual in that no output transformer is required which is why the speaker impedance is quite high and also, I believe, critical to the correct operation of the circuit.

I may be able to copy the details I have and post them on here or send them to you via PM if that would help.

Regards

Andrew

That's interesting, yeah I'd like to see what you have on that. More information is always welcome.

Originally Posted by Nuvistor

There is also a good article in Radio Constructor about this type of audio stage.
https://www.americanradiohistory.com...RC-1961-11.pdf

This article was written with the help of Mullard.

going to give this a read, thanks

[Maarten]

My apologies, for some reason I misinterpreted and thought you had ordered all valves!

Of course substitutes for repairing are just fine in my opinion, repairs are an essential part of a sets history. If the tube and chassis are bad or missing I'd even consider giving one a pass on painting the set pink and mounting an LCD in it :O

I gather data for historical research and for identification of parts (Philips doesn't use the same article codes on parts in a set as in the service manuals and spares lists). Part of the historical research is noting down pretty extensive data on each set that passes through my hands. Date and production codes on valves and some selected semiconductors is one aspect of that and for that it's always nice to have at least some originals in a set. Once I have enough, it might be fun to apply some statistics. Up to now I only do some statistics on serial numbers and production dates of complete sets.

Edit: C615 is likely to be a paper capacitor, possibly C612 and/or C616.

[Kyle__B]

C503 replaced, PCL86 replaced, no change noticed. Replacing a multi section cap with individual ones is a bit awkward.

PCL805 coming soon hopefully.

[simpsons]

Kyle

I thought C503 was the multi capacitor, which section did you replace or is this a mistake?

Have you bridged the C503a section as recommended?

Chris

[jayceebee]

Looking at your circuit diagram the set looks as though it uses a second PCL805 in the field stage. Have you tried swapping them?

John.

[Nuvistor]

There was a Bush BW TV135R that had the frame and sound on a small PCB, the screws earthing the PCB to the chassis oxidised under the screw heads and frame 50Hz came through the sound. Altering the frame hold change the frequency of the sound.
Just a thought is it the power that’s causing the hum or another item.

[Kyle__B]

Originally Posted by simpsons

Kyle

I thought C503 was the multi capacitor, which section did you replace or is this a mistake?

Have you bridged the C503a section as recommended?

Chris

Originally Posted by kyle__b

Replacing a multi section cap with individual ones is a bit awkward.

Obviously i replaced all of them it's an all of nothing kind of deal.

Swapping the PCL805s has either made the 50Hz din a little worse or done nothing to it, hard to tell because it's night time now so there's no other noises in the house to hear.

Swapping them also made the picture vertically squashed, like letterbox bars when you watch something filmed in widescreen. The picture gradually expands if you leave it to warm up.

Hope my two new ones come in the post soon.

[simpsons]

Hi Kyle

Got it. When you said replacing a multi capacitor is a bit awkward, I read it as though you hadn't done it so far.

The low height caused when swapping over the PCL805 may not mean much if the hum is still there. It's just that the valve is low emission which when working as part of the sound output stage wasn't noticed.

I'm beginning to question if the hum is, as suggested re Bush TV fault, is something "more down to earth" - no pun intended.

One last point and perhaps should have been asked earlier, did this fault suddenly happen or has the hum become noticed over a period of time?

Chris

[Maarten]

If it isn't in the supply line and not a heater short, it must be in the ground, not much choice there, I think.

[Kyle__B]

We'll find out if it's a heater or not when I get the new tubes... the two that are in there now are original, so they should be just about equally worn out, surely?

It's always hummed the whole time I've owned it, over a year now. It had been out of use for a long time until then judging by the long wire someone had tried to use as an analogue Arial.

The idea of the noise coming through the neutral side is interesting but I've no idea how I'm supposed to find or remedy that. The chassis is all one PCB, everything's soldered except for the valves and the wires that go off to the controls on the front, which have plugs.

[Kyle__B]

Originally Posted by Nuvistor

There was a Bush BW TV135R that had the frame and sound on a small PCB, the screws earthing the PCB to the chassis oxidised under the screw heads and frame 50Hz came through the sound. Altering the frame hold change the frequency of the sound.
Just a thought is it the power that’s causing the hum or another item.

I just did a little experiment.

At the moment I'm feeding the video amp from a playstation. Between the two is a little battery powered headphone amplifier, so I can control the strength of the video signal.

The only place I could think of where there could be a dodgy ground is in the front controls. The volume and power are on one knob. The audio amplifier connects to the volume and tone knobs with wire B6 for signal and B5 for it's earth. I disconnected them, and connected up to a walkman, so I can play a music tape into the TV.

Music comes through clear, buzzing is present but very minimal, makes a selection of crazy raygun noises if I lower the video signal enough to start the picture rolling. Strange beast.

[Kyle__B]

After that little experiment I put it back to normal. Turning the volume back up from zero I heard a funny crackle noise. Gave the volume knob a wiggle (rocking motion, not turning it) and the hum got louder and quieter.

I'm going to go spare. If it's the volume knob I would've liked to learn this about sixty quid earlier.

[simpsons]

Hi Kyle,

On the plus side you have replaced C503 which in many vintage TV's equivalent part would be in need of change. The PCL805 was low emission anyway.

Now, back to the problem.

You say wiggling the volume control the hum got louder and quieter, that in itself isn't unusual. I'd like to suggest that we go back to basics and you narrow down the frequency of this "hum."

Should you have either a PC, Laptop or smart phone, Google "online tone generator" and select 50Hz. Listen through good in ear 'phones. If this is the same sound you are hearing through the TV speaker, good. We are all on the same page, if not, hmmm, then its back to the drawing board. Try and find the frequency that is near to the sound that is bothering you.

Chris

[simpsons]

Kyle, I forgot to mention that when you grounded pin 8, this should have eliminated any issues from earlier stages, including the volume control.

Now, you say that the fault has been with the set since you purchased it and so it is possible that there is an earthing problem but I suggest until the frequency of 50Hz is confirmed, I would hold on changing other parts "just because they might be the cause."

Chris

[Maarten]

Also, even if the frequency is (roughly) 50Hz, is it from the frame output or from the mains?