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Old 29th Mar 2020, 6:56 am   #41
Kyle__B
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

I'd listened to a tone generator before I registered here and it was a 50Hz sawtooth then, at constant volume no matter what. No matter at all if volume was off or maximum.

(https://www.szynalski.com/tone-generator/)


To recap:

TV was humming 50Hz equally loud no matter what the volume knob was set to. It was loud enough to be very distracting.

grounded pin 8 of PCL86 temporarily, no change to symptom
Replaced PCL86
Swapped PCL 805s, found they're low emission, one more than the other
Replaced all sections of C503
wiggled volume knob, saw it made a difference, gave it few good blasts with canned air

All this has actually helped, but I'm not sure if it was one of these things, all or several of them.

Right now the speaker makes a quiet 50Hz SINE if you put your head right to the speaker. If you're a foot away it's inaudible. Turning the volume up a 50Hz SAWTOOTH gradually fades in. At maximum volume this is still quiet, you can hear it at comfy watching distance but it's nowhere near as bad as it used to be. At a sensible volume level you can barely hear it when the program is silent and it gets drowned out by the sound.

It's good enough that I'd call it fixed, I just wish I'd been more thorough testing it and writing down what I noticed after every change instead of just turning it on and listening for if there was a noise or not. I like to know why a repair worked instead of just brute forcing my way through by replacing every part that could possibly show a symptom, but I was too impatient to do what I needed to do to learn this time.

It's funny, I'm a good push bike mechanic, and for the last ten years I haven't owned a bike that I haven't completely restored or built from second hand parts. I know how to find what's wrong in a sturmey-archer hub if it slips out of gear, rather than to spend money replacing one part after another until it stops doing that. But with electronics I fall back on the bad habit.

Maybe that's old fashioned to worry about. A friend in a bike shop told me that with the newest three speed gears from Shimano if there's any problem with them at all they just replace the entire unit. They're considered disposable and sealed for life, and here's me with a design from 1936 that needs a teaspoon of oil putting in every six months.
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Old 29th Mar 2020, 10:14 am   #42
simpsons
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Kyle

This is good news.

You may wish that you had solved the problem in logical steps but it is so much easier be wise after the event.

Also, to have a little more knowledge about how Philips sought additional markets for televisions by improved audio, for example, is just another example of the success of them and other European Manufacturers in creating additional demand Europe wide when we were churning out 405 line television sets only the UK and viewers in Hong Kong could watch.

Something else, with all your talk about gear boxes, mechanical TV enthusiasts now know who to turn to!

Good luck

Chris
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Old 29th Mar 2020, 1:01 pm   #43
Maarten
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

I suspect in case of this set it was more about the cost (output transformer) or even tradition. Dutch designed sets have used OTL audio stages before while the German equivalent chassis of the time used a single PCL86 or even EL95 with a transformer.
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Old 29th Mar 2020, 2:25 pm   #44
Kyle__B
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

I don't think anything in this was done for cost savings. You should see the tuner, it's got six push buttons that select pre programmed channels across four bands with a mechanism that'd frighten charles babbage. The 1969 brochure does a lot of bragging about this model.
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Old 29th Mar 2020, 8:33 pm   #45
Maarten
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

You'd be surprised at how important cost savings were for Philips (or are for mass production in general). The tuner, while relatively high end was an off the shelf part, also used in the K6 and K7 colour sets so not a special development - there probably wasn't anything cheaper available anyway (except for the old presetless tuners which by that time were only used in the Americas and Japan). The later version of this chassis (pcb already prepared) actually used a varicap system that might have been slightly cheaper but also more comfortable to operate. I think the second PCL805 was actually "for free" as the triode part was used elsewhere and valves were still very cheap to produce for Philips (they likely were the largest producer worldwide for most of the time that valves were current). Weighing the costs between that valve versus a few transistors for the triode part plus an output transformer would have resulted in the OTL solution being cheaper - as long as the 800 ohm speakers were current production. As soon as those were discontinued the use of an output transformer and a low impedance speaker would have been a no brainer. I think this was the last OTL design, maybe except for some multi/france set as those were often one generation behind. The 1972 transistorised K9 colour chassis used 8 ohm versions of the same speaker with an output transformer. Strangely, all colour sets used a single ended output stage with a transformer. Might have had something to do with connecting an external speaker or headphone to a live chassis.

Last edited by Maarten; 29th Mar 2020 at 8:54 pm.
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Old 31st Mar 2020, 3:45 pm   #46
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Now I'm livid. Those PCL805s I ordered came today.

I bought Philips, Mazdas arrived. Seller has listings for both kinds, I thought I'd give them a go anyway. After all, interchangeable parts.

I plugged them in. I turned it on and sat back for it to warm up. A horrible loud buzz came out with several popping and cooking sounds. The waft of burned electrics hit my nose.

I've put the old ones back.

Last edited by AC/HL; 31st Mar 2020 at 4:04 pm. Reason: Rule C4
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Old 31st Mar 2020, 4:24 pm   #47
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Are you entirely serious "AC/HL"?

Why is there a rule against saying that these new valves damaged my TV and that there's no longer any raster?

Because that's what you've deleted from my post.
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Old 31st Mar 2020, 5:21 pm   #48
Kyle__B
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

DY 802 does not light up.

DY 802 is a diode for what looks like a stone age flyback transformer, which makes me think that either that transformer has been killed or something which controls it has been killed. I've seen transformers get cooked before, it smelled like this.

This is beyond my capabilities.
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Old 31st Mar 2020, 8:05 pm   #49
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Quote:
Originally Posted by Kyle__B View Post
Why is there a rule against saying that these new valves damaged my TV and that there's no longer any raster?
Of course you can say that, and you have done, but we don't allow any discussion about eBay or eBay sellers.
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Old 31st Mar 2020, 8:42 pm   #50
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Itís unlikely the valves have killed the LOPTX, itís more likely if they are faulty they damaged the power supply.
Look carefully for burned resistors in the power supply, you will probably be able to see them.
Itís quite possible that the replacement valves are ok and itís another fault caused the problem, it happens, just moving the chassis in a vintage TV can break insulation on wires etc.

A careful check for burnt items hopefully will spot what part as burned, then you need to trace out why.
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Old 31st Mar 2020, 8:42 pm   #51
Kyle__B
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

Quote:
Originally Posted by Nuvistor View Post
It’s unlikely the valves have killed the LOPTX, it’s more likely if they are faulty they damaged the power supply.
Look carefully for burned resistors in the power supply, you will probably be able to see them.
It’s quite possible that the replacement valves are ok and it’s another fault caused the problem, it happens, just moving the chassis in a vintage TV can break insulation on wires etc.

A careful check for burnt items hopefully will spot what part as burned, then you need to trace out why.

I've looked and nothing is visibly burned, as it is now with the old valves back in the audio section is still working perfectly. The 805s are in horizontal and vert sync and I'm willing to bet they can cause stress. I doubt very much that just unplugging two valves and plugging two new ones in has made a wire come loose because the chassis has been in the same position for weeks.

I'm not touching this tv again for another few days. I need a holiday from it.

Last edited by Kyle__B; 31st Mar 2020 at 8:47 pm.
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Old 31st Mar 2020, 9:03 pm   #52
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

I thought the valves were for the sound section.
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Old Yesterday, 9:21 am   #53
Kyle__B
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Default Re: New to valves, Dutch Philips TV with 50Hz speaker buzz

PCL86 is only sound, one PCL805 is both sound and sync and the other PCL805 is only sync.

Last night someone just died, the TV can wait. I'm writing up some notes to remind myself where I was with it and I'll carry on after the funeral.
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