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Old 4th Sep 2015, 5:06 pm   #41
boxdoctor
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Default Re: Philips B3G63A

As you say, Paul the design is a bit odd. Odder still when you see that the series resistor is in fact 18 Kohm! I cant see that it has much effect in practice. Par for the course with Philips, as you rightly said! Tony
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Old 4th Sep 2015, 8:06 pm   #42
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Default Re: Philips B3G63A

O.k guys - placed order for my first batch of capacitors including a 1000pF 1000V Ceramic Capacitor for C66, the tone correction cap across T1.

Still need to find suitable 630v replacements for:-

C51 (5μF)
C65 (100μF)
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Old 4th Sep 2015, 8:22 pm   #43
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Default Re: Philips B3G63A

These are electrolytic caps and don't need such high ratings. Just use whatever the original ratings were or better, which will be printed on the side somewhere. I think the 5uF discriminator cap only needs to be 50V or thereabouts. C65 is a cathode bypass cap and again 50V should be fine, but replace like with like.
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Old 6th Sep 2015, 9:14 am   #44
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Default Re: Philips B3G63A

Nice to see your enthusiasm growing, Donald. keep at it.
The reward of a well-restored radio and the satisfaction of having done that yourself is something to be savoured.
I've got my VHF dial re-strung now, but my project has to go on hold for a day or two, as the bench is to be occupied by more pressing (paying) jobs at the moment.
But I'll be following your posts on the forum. Tony
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Old 6th Sep 2015, 10:45 am   #45
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Default Re: Philips B3G63A

Thanks for your words of encouragement Tony - also to Paul and others for their ongoing support and patience.

Having restored a number of items of "modern" hi-fi equipment, laptops, iPhones and cameras, I'm well acquainted with the pleasure a fully working device can bring! Perhaps it's an age thing but I tend to rail against our "throw away" society.

Anyway, back on message, further cleaning last night and I noticed that the VHF drive cord was loose, not taut like the other cord. My heart sank of course as I knew how difficult it would be to replace this! Spent a long time tracing the circuitous route the cord takes looking for a break and noticed it had slipped off the pulley at the Tuning knob end. Just need to work out how to get in there?

Still checking the details of my two large electrolytic caps - I can read the 100uf one o.k. but the other 5uf one may need to come out? I'll be back for further advice shortly on suitable replacements.
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Old 6th Sep 2015, 3:08 pm   #46
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Default Re: Philips B3G63A

Donald,

Philips specifications on the 100uF and 5uF electrolytics in your set are 12 WVDC and 75 WVDC respectively. So you'd want the modern equivalents of 1 x 100uF at 16V and 1 x 4.7uF at 100V (though I can't imagine the original circuit really has 75V going through this capacitor).

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Old 6th Sep 2015, 9:31 pm   #47
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Default Re: Philips B3G63A

Thanks Andrew - do you know if these available from the BVWS Spares Dept?

I've just become a member.
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Old 7th Sep 2015, 9:00 am   #48
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Default Re: Philips B3G63A

Hi Donald,
Please bear in mind that electrolytic caps that are used on much lower voltages than their rated voltage will tend to de-polarize over time, and lose their capacity. Good priced 100uf 25v (The actual voltage across it willl be considerably less than that) is available here http://www.cricklewoodelectronics.co...ics-Axial.html The 5 uf was original , and, in my set, rated at I think 6 volts!. It has,as I said, gone in the bin, so I cant be sure. It is unlikely to get more than about 5 volts across it, even on a strong FM signal. One rated at 10 or 16 volts would suit nicely. Keep at it! Tony
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Old 7th Sep 2015, 1:25 pm   #49
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Default Re: Philips B3G63A

Another small order going off to Cricklewood - a pity that p&p are so high!

Promise to lay low for a while, do lots of reading and get some actual upgrade work done.

Thanks again meantime ...
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Old 7th Sep 2015, 2:57 pm   #50
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Default Re: Philips B3G63A

Quote:
Originally Posted by boxdoctor View Post
(The actual voltage across it willl be considerably less than that) is available here http://www.cricklewoodelectronics.co...ics-Axial.html It is unlikely to get more than about 5 volts across it, even on a strong FM signal. One rated at 10 or 16 volts would suit nicely. Keep at it! Tony
Be careful....Depending on signal strength it is easily possible to get over 30 volts across the discriminator cap....I've measured it. Don't forget that manufacturers will always use the lowest voltage component they can get away with to keep costs down and if they could have fitted a 25V component, they would have done. If they fitted a 75V type, they obviously expected higher voltages than around 30V.

To be safe, I'd fit a 50V or 100V type which in all honesty, don't cost much (if any) more than a 25V type.
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Old 7th Sep 2015, 3:41 pm   #51
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Default Re: Philips B3G63A

Many people feel that using an excessively-rated electrolytic is no bad thing, so long as it's never asked to withstand its rated voltage after years of being used at lower voltages.

Or that's how I understand it.
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Old 7th Sep 2015, 5:16 pm   #52
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Default Re: Philips B3G63A

If you aren't certain of the component operating voltages including under fault conditions it's always best to treat the original component rating as a minimum but not go up too much. In this case I would be happy to use a 100V cap but would be a bit wary of using a 250V cap, though it would probably be OK.

This only applies to electrolytics of course. With plastic film caps it doesn't matter how overrated they are.
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Old 7th Sep 2015, 11:30 pm   #53
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Default Re: Philips B3G63A

As I understand it, the recommendation for Electrolytics is not to go below 10% of the rated voltage.

Last edited by AC/HL; 8th Sep 2015 at 3:47 pm. Reason: Clarified
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Old 8th Sep 2015, 11:21 am   #54
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Default Re: Philips B3G63A

Hi guys - thanks for all your contributions.

I know I promised to lay low for a while but ...

This is what I've ordered for the electrolytics: -

C51 (5μF) - Ordered a 4.7uF 100V Axial Electrolytic Capacitor

C65 (100μF) - Ordered a 100uF 25V Axial Electrolytic Capacitor

Still a bit unsure (and over cautious?) about C66 (0.001μF) which is connected across output transformer T1, what the correct voltage should be and which type should be used to replace it? I've ordered a 1000pF 1000V Ceramic Capacitor but noticed in another Thread that someone had used an orange dip 1500v capacitor on the output transformer??

Next question - I need to get access to the dial cord and pulleys as the VHF cord has jumped off although it's still intact. How do I safely remove the dial glass which appears to be secured by rubber grommets - don't want to force it and risk cracking the dial glass? If I can remove the dial glass I will ensure I take a high quality scan - is there a library for such items?
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Old 8th Sep 2015, 12:07 pm   #55
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Default Re: Philips B3G63A

1kV will be fine for C66. This was the standard rating for this component, though it does no harm to fit a higher rated replacement of course. I bought a cheap bag of 0.01uF 1.6kV polyester film caps from an eBay seller ages ago which I use as tone correction caps.
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Old 10th Sep 2015, 10:50 pm   #56
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Default Re: Philips B3G63A

Quote:
Originally Posted by DonaldStott View Post
Next question - I need to get access to the dial cord and pulleys as the VHF cord has jumped off although it's still intact. How do I safely remove the dial glass which appears to be secured by rubber grommets - don't want to force it and risk cracking the dial glass? If I can remove the dial glass I will ensure I take a high quality scan - is there a library for such items?
Hi Donald, My dial glass came off unexpectedly easily by simply gently pressing the rubber fixing "grommets" (You will find they are not actually grommets when you get it off) all the way round towards the control shaft with a broad bladed screwdriver, at the same time gently easing the glass off over the lip of the "grommet" in each case. Re-fixed with the aid of a smidge of silicon grease. Gently does it! A useful item to have is here -wonderful tool to manipulate drive cords etc,http://cpc.farnell.com/pro-s-kit/1pk...ook/dp/TL00192
Should be able to do more on mine next week. Tony.

Last edited by boxdoctor; 10th Sep 2015 at 11:13 pm. Reason: Additional information
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Old 11th Sep 2015, 9:40 am   #57
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Default Re: Philips B3G63A

Thanks Tony - I'll give it a go tonight although I'm still very cautious. I'd be happier using some sort of wooden implement rather than a flat blade screwdriver!

Liked the link for the Spring Hook but I'm just going to borrow a crochet hook from you know who and see if that does the business.

Having trouble measuring some resistors as it's really packed under that spiders web of components and wires. Currently, identifying and measuring R15 (56 kΩ) is giving me grief - I think this is the EF85's (V4) screen grid feed resistor that has been identified in other Threads as something to be checked ... ?
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Old 11th Sep 2015, 10:19 am   #58
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Default Re: Philips B3G63A

Hi Donald, I may be telling you something you already know, forgive me if so, but be wary of measuring resistors in circuit. as you are also measuring the resistance of the network that they are connected into. Always disconnect one end for an accurate reading.
Spring hook very highly recommended - I have two. I bought a spare when I ordered mine in case I lost the first one. As luck would have it, they are both still in the tool box after >25 years!
Still not got back to my VHF dial drive yet. Cheers, Tony.
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Old 11th Sep 2015, 11:24 am   #59
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Default Re: Philips B3G63A

You can usually make a rough check of value with the resistors in circuit. I wouldn't disconnect them in the absence of a fault as it is a very substantial job.

The in circuit readings will be more accurate once the caps have been changed.
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Old 11th Sep 2015, 11:54 am   #60
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Default Re: Philips B3G63A

Resistors usually drift HIGH in value, often by 50% or so. Whether this is a problem or not depends on what the resistor's job is. Best to ask for advice if unsure.

If any seem LOW, assume you're getting a false reading because the resistor is being shunted by something that's allowing DC through it, e.g. a coil. In this case, it would be in order to disconnect one end of the resistor and re-test, if you're suspicious. I tend not to bother though, particularly if the other resistors in the set seem OKish.

If any seem to SLOWLY INCREASE FROM LOW TO HIGH, this is probably because there's a capacitor which is being charged-up by the battery in your meter. The reading will usually be fairly accurate once it's stabilised, but this can take a while with a big capacitor.

Note that all resistance readings must be done with the power off and the big capacitors fully discharged. Also, use clips for higher-value resistors, as if your fingers touch the probes, your body's resistance can affect the reading (quite significantly if you're measuring megohms).

Good (e.g. Fluke) meters are much better at taking resistance measurements quickly than cheapies, which can take a good few seconds to stabilise and can get confused by big inductors (e.g. transformer windings).

Nick.

Last edited by Nickthedentist; 11th Sep 2015 at 12:00 pm.
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