Restoration novice. Philips B3G63A.

[Nuvistor]

Do you know about CPC in Preston, just up the M6 or M61 depending whereabouts in Wigan you live.

https://cpc.farnell.com

Resistors, capacitors etc.

[LyntonP]

Frank
No that is a new one on me. Just had a look on the website. interesting.
I live in Ashton in Makerfield close to Haydock Park race course, so very handy for the M6.

[LyntonP]

Quick question
Is 4.7KpF the same as 4700pF?

[cathoderay57]

Hi Lynton. If you are planning to expand your interest in vintage radios and restore more sets then it would be worth considering joining the British Vintage Wireless Society https://www.bvws.org.uk. As a member you can mail order electrolytic capacitors and bulk quantities of poly film capacacitors of values commonly used in most sets. There are other substantial benefits including an excellent magazine and details of BVWS auctions - the one at Golborne Warrington is not far from your location. Kind regards, Jerry

[cathoderay57]

Originally Posted by LyntonP

Quick question
Is 4.7KpF the same as 4700pF?

Most likely yes, if it's an old component. These days you're more likely to find 4.7nF or 4.7 nanoFarads which is the same value

1000pF = 1nF = 0.001uF

Cheers,
Jerry

[Nuvistor]

The Golborne BVWS meet is a worthwhile visit, you have just missed one but there is usually one in April. I only found out about the Bickershaw rally after the event. Again both very close to were you are in Ashton.

It’s about 10 years since I used CPC, if you go, make sure the parts are in stock and unless it’s changed be prepared to wait at the counter. I used to pass the place every day going to work. It’s very easy to get to, not far from the motorway junction 31A and Asda in Fulwood.

[dave walsh]

The Radiophile has only recently gone on line Lynton. The Teaching Workshops page might be worth a look and locations are often in the Newport, area which should be relatively handy down the M6 from Wigan. Unfortunately the current one is taking place over this weekend ie today and tomorrow

Dave W

[julie_m]

Originally Posted by LyntonP

The most common piece of advice I have read is don’t plug the set in until all the old capacitors have been changed.

That's great advice in theory, but lousy advice in practice.

There is usually at least one capacitor in any piece of equipment using valves which must be replaced before the set is powered. But besides these critical capacitors, a set will not suffer lasting damage running for a short while with a faulty capacitor.

Now, everything you do has a certain probability of going wrong. Take replacing capacitors in a radio, for example. The more you replace in a single continuous run without testing the set to see if it still works, the greater the probability that you will either fit an incorrect value part, or miswire one or both leads.

If you replace all the capacitors without ever testing the set, and it doesn't work when you eventually switch it on, you will have no way to know whether it was already faulty beforehand, or whether you made some wiring error that stopped it from working.

Also, some capacitors are more unreliable than others. The capacitors used in tuned circuits tend to be highly stable mica types. And if these are changed, the set will be put out of alignment; which requires special tools to fix.

So as a compromise, the recommended procedure is first to replace just the most critical capacitor (in a simple four-valve plus rectifier" radio set, that is the DC blocking capacitor to the grid of the audio output valve), then power the set up to test it. You probably won't get any stations coming through just yet, but at least you can take some DC voltage measurements and use a second set to verify whether the local oscillator is running without fear of the one you are working on self-destructing.

Once the set is something like working, then you can replace capacitors; one at a time, and starting with the ones that won't affect the alignment.

[LyntonP]

As to the working voltage (VW) of replacement capacitors, that is stated on the maker's data, and you'll see that apart from one (C55 - 800VW)

Sorry David don't know how to do a quote correctly.
Why do you say that C55 (manufacturers sheets) has a working voltage of 800 volts when the circuit diagram states that the voltage on the anode of V6 EL84 is 230V for AM and 240V for AM?
Should I be looking at a total positive to negative voltage or is there another reason?
Managed to track down some capacitors and a new panel lamp from a place in London. Postage almost same value as components!
Cheers
Lynton

[Andrewausfa]

Without looking I bet that's the or a tone correction capacitor. My understanding is you may get voltage spikes superimposed on a DC voltage on it which is why you'd normally see much higher rated capacitors in this position i.e 1kV rated. I'm sure someone can explain in more detail.

A modern 1kV is what you should put in there to protect your rather precious output transformer, if you look I suspect you'll find one end of your C55 is connected to your output transformer. You won't likely get a 800v capacitor these days.

Andrew

[Nuvistor]

The audio waveform can have lots of sharp transients, this will create a back EMF that can be much higher than the HT. The speaker provides a load which damps the back EMF but it can still be considerable, depending on the size and shape of the waveform.

This is the reason a valve amplifier should not be used without a load, speaker or dummy load, the back EMF can damage the output valve and transformer.

[AC/HL]

Originally Posted by LyntonP

Sorry David don't know how to do a quote correctly.

Chapter and verse: https://www.vintage-radio.net/forum/...ad.php?t=15093

[LyntonP]

Several verses!!!
Thanks Bill
Lynton
Think I have the correct method now.

[LyntonP]

Finally got some time to work on the radio yesterday. Changed the three capacitors as suggested and lo and behold the radio works!
Powered the set up with a “dim bulb” in circuit and there was hardly a glimmer from the lamp.
Well it works on LW and MW but not a peep on FM.
Sounds very nice but does distort somewhat when the volume is turned up.
Had a small crisis when the FM dial/tuning cord decided to jump off the pulley on the tuning capacitor, but I popped it all back on ok. I think the cord is worn as it does not grip the brass pulley on the tuning knob very well (AM tuning works very well).
Think I got to the set just in time as one of the capacitor leads was on the point of a short, with the insulation tubing ready to fail.
So on to the FM. Any suggestions?

[Nuvistor]

Is the distortion and lack of FM due to using the lamp limiter?
If not use voltage checks and signal injection if you have the test equipment.

[Aerodyne]

Don't forget that the lamp will be limiting the HT voltage, unless you've now bypassed it and have connected the set fully to the supply. The audio distortion could be due to low HT with the lamp, and could be one possible reason for the lack of FM performance.
Just in passing, I recall one similar Philips set I worked on where a preset variable capacitor (miniature type, probably what is known as a 'beehive') was earthed to the chassis via its mounting bracket. This had corroded on the meeting faces between the bracket and the chassis, causing a 'dead' FM section. Sometimes the smallest thing can have a large effect.

Just thought I'd mention that before you delve too deeply into fault locating.

Tony

[LyntonP]

Originally Posted by Nuvistor

Is the distortion and lack of FM due to using the lamp limiter?
If not use voltage checks and signal injection if you have the test equipment.

Frank I did take the lamp out of circuit and checked the ac voltage being applied and it was a shade under 240V.
Both valves in the FM section are lighting up.
Dont have a signal injector at the moment.
Lynton

[Nuvistor]

Tony’s suggestion is worthwhile checking then check the voltages for large differences from the manual.
You may be able to hear the LO in another radio.

[LyntonP]

Originally Posted by Aerodyne

Just in passing, I recall one similar Philips set I worked on where a preset variable capacitor (miniature type, probably what is known as a 'beehive') was earthed to the chassis via its mounting bracket. This had corroded on the meeting faces between the bracket and the chassis, causing a 'dead' FM section. Sometimes the smallest thing can have a large effect.
Tony

The FM board is separate to the main chassis but shares a common ground I used a screwdriver to connect the two chassis together and the FM came to life.
Lynton

[Nuvistor]

Well done, nearly there, find the bad connection then just the distortion.