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Old 24th Oct 2011, 3:37 pm   #101
Neil Purling
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Default Re: Philips B3G75U

Working voltage about 350-400V 2X the max HT voltage at that point I would have thought would be about right
What rating is the defective component anyway? A modern component would probably be physically smaller. The problem may be actually getting a high voltage capacitor.
Try somewhere that services guitar amplifiers if you are really stuck.
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Old 24th Oct 2011, 4:58 pm   #102
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Default Re: Philips B3G75U

Good to hear that your set is working again, well done.

It is unusual for one of these tubular ceramic capacitors to fail in this way. They are more likely to be found physically broken, or pressed too tightly against something else, which penetrates the paint coating, leading to a short-circuit. In other words, there is no need to fear that the other tubular ceramics in your set will go the same way.

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Old 24th Oct 2011, 8:04 pm   #103
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Default Re: Philips B3G75U

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It is unusual for one of these tubular ceramic capacitors to fail in this way.

Absolutely agree. However I have had the odd Philips ceramic fail. It led me a merry dance in a Philips TVette B/W portable but that's another story....

Tha capacitor in question was a decoupler in one of the higher voltage areas of the set...can't remember where now...I'm going back over 30 years. Anyway it was showing an intermittent reading from a few ohms up to several K and one of the 'boffins' from the back room decided to investigate. He found that it was tracking between the ceramic body and the outer connection and showed me under a powerful magnifier. The tracking could be seen quite clearly when a voltage of 100 or so was applied across it.

Never forgot that....


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Old 25th Oct 2011, 5:56 am   #104
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Default Re: Philips B3G75U

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Working voltage about 350-400V 2X the max HT voltage at that point I would have thought would be about right
What rating is the defective component anyway?
I don't know unfortunately. There isn't any comment in either the Trader or manufacturer's sheet that I can find. The thing itself is simply marked 1k, 20%. No mention of voltage at all.

I'll just have to see what is available from the local shop - Always a bit hit and miss to say the least when it comes to older kit.
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Old 25th Oct 2011, 7:52 am   #105
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Default Re: Philips B3G75U

Out of interest here's the culprit.
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Old 25th Oct 2011, 8:39 am   #106
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Default Re: Philips B3G75U

I've got a sneaking feeling that these were rated between 300V and 500V depending on their size. If it's about 1/4" long or so then it's 300. If it's the longer one at about 1" then it's 500V. Unfortunately I don't have the older data books anymore.



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Old 26th Oct 2011, 1:45 pm   #107
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Default Re: Philips B3G75U

So just to close the loop.

Went to the shop today and they had 500V disc ceramics - much smaller than the original which is no bad thing given the lack of space available. Picked up a couple and a new 2.2k resistor for about 50p. Fitted them and the set is working perfectly well again. Many thanks again for the help - It's amazing.
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Old 26th Oct 2011, 4:09 pm   #108
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Default Re: Philips B3G75U

You've done well to keep your patience with that set! Mostly stock faults but that last one was definitely a bit unusual.

These are quirky sets, with the permeability tuning on all bands, and that crazy wavechange linkage. Add to that mix the 19V 90mA dial lamp, and you have a typically infuriating Philips design. However they do work well, with good drift-free performance on FM, and considering the compact cabinet and AC/DC design, they don't run as hot as you would expect.

The attached document, printed on slightly yellowed card and folded into three, should finish the job nicely.

Roy
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Old 26th Oct 2011, 7:43 pm   #109
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Default Re: Philips B3G75U

Excellent job. Well done and a lot of experience gained!


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Old 27th Oct 2011, 7:48 am   #110
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Excellent job. Well done and a lot of experience gained!


Rich.
Absolutely! All good learning and experience.
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Old 27th Oct 2011, 8:03 am   #111
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Default Re: Philips B3G75U

Roy, thank you very much for the manual - a very nice touch and there is some handy information there too.

I suppose I have no choice but to be patient with this set as if I want my Radio 5 on a valve radio I have no other choice around here! One of the main reasons I have it is that it is small enough to be put in a suitcase.

You are certainly right about that wavechange switch mechanism. As good as an example of over engineering as I have ever seen. It didn't work properly at first but to my relief tightening the grub screws and a bit of WD40 restored it to working order immediately.

The bulb worries me a little. Are they available at all? I gained the impression that the thermistor was to allow the set to continue working when it fails so perhaps it's not such a severe problem waiting in the wings.

I am happy enough with the performance. It's not amazing of course but it is perfectly good enough for a workaday radio.
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Old 27th Oct 2011, 10:39 am   #112
Roy
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The bulb worries me a little. Are they available at all? I gained the impression that the thermistor was to allow the set to continue working when it fails so perhaps it's not such a severe problem waiting in the wings.
The lamp is shunted by the thermistor and parallel 146 ohm resistor, so the receiver will indeed work without it.

The genuine bulbs are no longer available, but 18V 100mA work fine, and are still on sale. My set has been running with one of these for quite a while.

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Old 27th Oct 2011, 12:28 pm   #113
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Default Re: Philips B3G75U

You may (or may not) be interested to know that the supplier H F Sheffield, whose name is stamped on the Operating Instructions posted by Roy, still have a shop in Abbots Langley High Street.

David
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Old 28th Oct 2011, 8:53 am   #114
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Yes, they are indeed still there in the same premises where the G97U was sold for 20gns in December 1959.
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Old 28th Oct 2011, 1:37 pm   #115
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Default Re: Philips B3G75U

And that was a pretty decent chunk of wages at the time. Perhaps two weeks average income? Just listened to Ella Fitzgerald singing "Mac the Knife" courtesy of NHK (local version if the BBC) on medium wave. It sounded excellent I have to say. I can understand how people actually danced in their living rooms to the radio.
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Old 28th Oct 2011, 3:00 pm   #116
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Default Re: Philips B3G75U

Going back to the bulbs. You can now buy AC/DC MES 6 and 12 volt Led bulbs. Some of them even have 100 degree viewing angles. With an added series resistor and a bit of colour filtering they might just do the job.

I have just checked again and there are even warm white ones available.


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Old 29th Oct 2011, 9:11 am   #117
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Default Re: Philips B3G75U

Well my interest is just in keeping the thing running 5 hours a day so I would be happy to look at any modifications needed to do that. I'm not even sure what is in there now actually. On switch on it glows quite brightly and then quickly fades to an amber glow. In full daylight it is hardly visible.

Have you got a link handy?

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Old 29th Oct 2011, 5:23 pm   #118
Roy
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Default Re: Philips B3G75U

Whilst LED replacement bulbs would be fine in an AC-only receiver, I'm not sure they would be entirely happy in this series heater chain, unless some additional regulation was included.

The brightness of the dial lamp in this particular model does vary enormously during warm-up - it starts off dull, increases steadily to what I would say is "alarmingly bright" then settles down to "about right". I haven't measured the voltage appearing across it during warm-up, but the range must be quite wide. I assume my set is working as it should in this respect - the thermistor seems in good condition.

The 18V 100mA bulbs work well and should be easy to obtain, but I have a few spares if anyone needs one.

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Old 29th Oct 2011, 6:48 pm   #119
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Default Re: Philips B3G75U

Most of these LED bulbs have a light output of 2000mcd or more. With that kind of output I would suspect the series resistor would end up under running the LED anyway I will do some sums from the circuit diagram.

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