Philips B3G75U - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

Wage Slave · 15th Sep 2011, 7:55 am

Ah, the buzz didn't really disappear.

It is still there. It might be some local interference - there is lots around here but I have turned off everything close to it.

The symptoms are as follows. It exists on all bands and all across all bands. At the lowest volume it isn't there. As you raise the volume it kicks in about at about a quarter volume, increases gradually and then disappears again about 7/8ths of the way round. There is a jump in volume just where it appears and disappears. It's clearly there but doesn't make a station unlistenable. It's just annoying and I'd like to fix it if possible.

Can anybody help with some ideas how I might go about it?

Reading around some other posts I have abandoned the idea of fitting a gram socket but a conversion to 100V might still be a good modification.

Wage Slave · 15th Oct 2011, 6:07 am

So, I don't think it is interference as it doesn't affect other radios. It's a noticeable hum/buzz that varies as I described above and affects all bands.

I think I might as well change the smoother/reservoir capacitor as I read this could cause the symptoms. One side of it measured a bit leaky with the old DVM at the start of the job so I suspect it wouldn't hurt to change it.

A couple of questions:

The Trader's Sheet gives its value as 50uf and 100uf and the service sheet from the link at the top of the page 50uf and 100pf (275V). Am I correct in assuming that the service sheet has a misprint. It should be 100uf as 100pf is way low.

It seems to me there are two options. Either stuff the can with two modern radial capacitors and refit the can or fit a new two in one capacitor designed for valve amps. The latter option would mean drilling a couple of holes in the chassis and fitting a capacitor clip.

I'm not too worried about maintaining original appearance just maintaining original function.

I can't find any 100uf/50uf units. Would fitting 100uf/100uf be OK? The existing can is C59 (100uf) and C60 (50uf) in the excerpted diagram attached.

Is there any service advantage in fitting a modern can type cap designed for the job over stuffing the old one with two standard 105 degree C radials?

'LIVEWIRE?' · 15th Oct 2011, 10:57 am

Speaking as a service engineer, I always replace reservoir/smoothing capacitors in valve gear with modern purpose made equivalents, available fromhttp://www.die-wuestens.deand other sources. The only thing to be aware of is that you don't increase the value of the reservoir capacitor(C60) beyond the maximum specified for the rectifier valve. The smoothing capacitor's(C59)value is less critical. Some dual capacitors are available as 'screw-in' types, which may fit in the original chassis hole without modification

Wage Slave · 15th Oct 2011, 11:51 am

Would 50uf/50uf be OK do you think?

There is one 50/100 available on the site you provided with a screw fitting which might be nice. I suppose the case being the - terminal is fine as well. I would just clean the chassis well round the hole and then the nut ensures a good contact between the can case and the chassis I suppose?

'LIVEWIRE?' · 15th Oct 2011, 6:02 pm

Quote:

Originally Posted by Wage Slave

Would 50uf/50uf be OK do you think?

There is one 50/100 available on the site you provided with a screw fitting which might be nice. I suppose the case being the - terminal is fine as well. I would just clean the chassis well round the hole and then the nut ensures a good contact between the can case and the chassis I suppose?

In case you need to connect an earth wire, those screw fit Capacitors usually come with a metal ring having a solder 'tag' for this purpose.

Wage Slave · 16th Oct 2011, 3:31 am

Thank you very much for that. These little questions must seem ludicrous to you guys but they are really important to me. I am tempted to spend the £20 or so for the screw in from the site you recommended as I am using the radio five or six hours a day so it is worth it.

I'll need to check the hole size but if it is a bit small a bit of filing should solve that and in the very unlikely event it is too big then washers should solve that problem.

Wage Slave · 17th Oct 2011, 7:55 am

Well. It turns out my local components store has good quality 350V 47uf and 100uf radials. Total cost about £4.50. Compared to £20 odd including delivery that was a deal. I was going to stuff the old one but realised I needed a 35 mm pipe cutter which I don't have.

In the end I found room under the chassis for them and refitted the old capacitor just for looks. All fine and good except it hasn't done anything for the buzzing. Looks like that 54 year old capacitor is still more of less fine!

The volume is a tad better I think but the buzzing remains the same. Applies to all wavebands at all frequencies. As you turn the volume control steadily it is very low at low volume and suddenly jumps as does the volume at moderate volume and then drops again as the volume suddenly jumps about two thirds of the way round.

Is this motorboating perhaps? I sort of think it is something with the audio stage as it is so volume sensitive and related to sudden jumps in amplification.

Any ideas?

Sideband · 17th Oct 2011, 8:34 am

Motorboating is a popping noise that can be slow or fast and your 'buzzing' doesn't sound like motorboating. Check the value of the volume control. If the volume control has a tone-compensating tap on it, check this as well. It's just possible that the control has changed in value. So check across the two outer tags first and you should find that it's within 10 or 15% of stated value. If there is a tap on the control ( a lot of Philips sets did), then check between each outer tag and the tap. The tap will also have tone correction components connected to it so check these as well.

If the control has drifted high in value then this can cause the sort of hum you are experiencing especially if the main track also forms the grid leak of the following valve (been there, done that etc)!!

If the volume control has an outer metal body, see if connecting this to chassis (if not already done) makes a difference. Also check any screened leads that may be fitted and check that mains feeds (to the switch perhaps) are kept away from the main volume control tags.

SB

Wage Slave · 17th Oct 2011, 9:48 am

Thank you. I'll look at that as soon as possible. Probably at the weekend.

Wage Slave · 22nd Oct 2011, 7:57 am

Well, thank you so much Sideband. I think that is my problem. The pot should be 2 Mohms. It measures OK across the two outside tags at 2.25 M. But if I measure from the slider to the end it is a very different story and one which fits the symptoms. It starts off OK at low volume and changes nicely to 2 M or so until it reaches a point where it jumps to 5 or 6. If I leave it, it then drops down to about 4M and remains fairly unstable. Continue turning it and numbers as high as 10M are seen before it slowly settles back to 4M or so. If you keep turning it suddenly drops to .8M, becomes stable and then tapers off nicely and smoothly to zero at the end of the travel. This fits very nicely with the appearance and disappearance of the hum/buzz and changes in the volume of the set.

I'm not sure what a tap looks like but I assume it would be an extra tag along with the standard three. In that case, there isn't one.

So, I'm hunting for a suitable replacement pot. Am I right in thinking it should be a log type rather than a linear type?

jjl · 22nd Oct 2011, 8:15 am

Yes, it should be a log pot for a volume control.

You may have difficulty sourcing a replacement; such things are getting harder to find in Europe and from your comments in other threads on the lack of interest in aged electronics in your location, a 2M log pot may be tricky to find in Japan.

Have you tried cleaning the pot with Servisol switch cleaner or similar?

John

Wage Slave · 22nd Oct 2011, 8:43 am

Quote:

Originally Posted by jjl

Yes, it should be a log pot for a volume control.

You may have difficulty sourcing a replacement; such things are getting harder to find in Europe and from your comments in other threads on the lack of interest in aged electronics in your location, a 2M log pot may be tricky to find in Japan.

Yes, plus there is the issue of the voltage rating of the switches. I have found this:

http://www.bowood-electronics.co.uk/...ts_id=652{2}92

and this

http://www.cricklewoodelectronics.co...cat=416&page=1

Both look possible. The only thing is that I will need 50 to 60mm of shaft as the thing is fitted a long way back from the front of the set. Unless I can find a sleeve or something to extend the shaft with a bit of the old one.

Quote:

Have you tried cleaning the pot with Servisol switch cleaner or similar?

Not really. I have squirted a bit near the contacts but the unit is pretty well sealed. How tricky is disassembly/reassembly? I'm leaning more to fitting a new or newer part as with anything mechanical, wear takes its toll. I have visions of trenches worn into the track over the years.

However, I could be persuaded - I am still very much learning how to do this.

Sideband · 22nd Oct 2011, 6:46 pm

Well most volume controls can be dismantled with care. From your measurments, it certainly seems like the control is causing the problem. Fortunately as the track measures OK then it could be an intermittent connection from the contact ring to the slider. You will have to remove the control completely so make a note of the connections.

Once the control is out, you should find that the casing of the pot that also holds the switch is held on to the front of the of the pot by bent-over lugs. Turn the spindle of the pot so the switch is in the 'on' position (this just makes it easier to reassemble). It should be possible to carefully bend the lugs up and separate the front part from the casing and switch assembly. You will then clearly see the track and slider with the contact ring. Spray the assembly with switch cleaner (no need to flood it) and work the control a few times to help clean any muck off the slider ring, contact and track. Some people like to apply some petroleum jelly to the track and slider. Check with your meter to see that the control is working correctly.

To reassemble, set the slider about halfway round by turning the spindle and simply reverse the dismantling procedure. Make sure the switch operates correctly and refit to the radio.

Hopefully you will now have a fully operating control. It takes longer to describe than to actually do the job!!

SB

Roy · 22nd Oct 2011, 8:36 pm

These Philips 2M pots are notorious for failing in this way. The problem is caused by tarnish on the contact ring, not by a failure of the resistive track. Some years ago, I managed to obtain some NOS pots of the correct type for these sets. Although unused, they were just as bad as the originals.

If you dismantle and clean the pot as suggested by Sideband, it will be fine. I have attached a couple of photos of an original control from a B3G75U so you can see what needs to be done. It's not at all difficult.

Hope this helps,

Roy

Wage Slave · 23rd Oct 2011, 2:14 am

Right, Thank you very much gentlemen. I'll get on with that today then and report back later.

Wage Slave · 23rd Oct 2011, 10:14 am

And so it was. I had to remove a few components to get it out but out it came and after a good clean it is back in and the radio is working fine now. Thank you all again - A very satisfactory way to spend Sunday.

Sideband · 23rd Oct 2011, 1:45 pm

Quote:

Originally Posted by Wage Slave

A very satisfactory way to spend Sunday.

...and it saved you the cost of a pot! Most volume and tone controls (even the concentric ones) can be dismantled and cleaned in this way. I did one only the other day for just the same problem. Not all controls respond but you have nothing to lose by trying it first.

I have another Philips pot to do sometime soon.

Enjoy!

SB

Wage Slave · 24th Oct 2011, 1:56 am

Oh dear. I spoke too soon it seems and I need more advice. I was listening on FM today when it stopped working and I noticed a funny burning smell. The dial light is much brighter than normal and the FM band is completely dead.

On MW it still works fine - oddly, perhaps even better than before. The dial light on MW seems dimmer than it was before.

Do these symptoms suggest any starting points?

Wage Slave · 24th Oct 2011, 6:31 am

Well, R7 is very nicely roasted and instead of reading 2.2k now manages 112 ohms.

Wage Slave · 24th Oct 2011, 8:37 am

So I replaced R7 and the dial lamp went dim again so I was hopeful. However, there wasn't any sound and then I noticed smoke rising from the chassis next to V1. Power off and an inspection reveals that the new resistor has been roasted as well.

So, something else is wrong and it is taking R7 out with it. I swapped V1 and V2 as they are the same but that had no effect. I'm a bit lost for ideas now.

15th Sep 2011, 7:55 am	#61
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Ah, the buzz didn't really disappear. It is still there. It might be some local interference - there is lots around here but I have turned off everything close to it. The symptoms are as follows. It exists on all bands and all across all bands. At the lowest volume it isn't there. As you raise the volume it kicks in about at about a quarter volume, increases gradually and then disappears again about 7/8ths of the way round. There is a jump in volume just where it appears and disappears. It's clearly there but doesn't make a station unlistenable. It's just annoying and I'd like to fix it if possible. Can anybody help with some ideas how I might go about it? Reading around some other posts I have abandoned the idea of fitting a gram socket but a conversion to 100V might still be a good modification.

15th Oct 2011, 6:07 am	#62
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U So, I don't think it is interference as it doesn't affect other radios. It's a noticeable hum/buzz that varies as I described above and affects all bands. I think I might as well change the smoother/reservoir capacitor as I read this could cause the symptoms. One side of it measured a bit leaky with the old DVM at the start of the job so I suspect it wouldn't hurt to change it. A couple of questions: The Trader's Sheet gives its value as 50uf and 100uf and the service sheet from the link at the top of the page 50uf and 100pf (275V). Am I correct in assuming that the service sheet has a misprint. It should be 100uf as 100pf is way low. It seems to me there are two options. Either stuff the can with two modern radial capacitors and refit the can or fit a new two in one capacitor designed for valve amps. The latter option would mean drilling a couple of holes in the chassis and fitting a capacitor clip. I'm not too worried about maintaining original appearance just maintaining original function. I can't find any 100uf/50uf units. Would fitting 100uf/100uf be OK? The existing can is C59 (100uf) and C60 (50uf) in the excerpted diagram attached. Is there any service advantage in fitting a modern can type cap designed for the job over stuffing the old one with two standard 105 degree C radials? Attached Thumbnails

15th Oct 2011, 10:57 am	#63
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Philips B3G75U Speaking as a service engineer, I always replace reservoir/smoothing capacitors in valve gear with modern purpose made equivalents, available fromhttp://www.die-wuestens.deand other sources. The only thing to be aware of is that you don't increase the value of the reservoir capacitor(C60) beyond the maximum specified for the rectifier valve. The smoothing capacitor's(C59)value is less critical. Some dual capacitors are available as 'screw-in' types, which may fit in the original chassis hole without modification

15th Oct 2011, 11:51 am	#64
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Would 50uf/50uf be OK do you think? There is one 50/100 available on the site you provided with a screw fitting which might be nice. I suppose the case being the - terminal is fine as well. I would just clean the chassis well round the hole and then the nut ensures a good contact between the can case and the chassis I suppose? Last edited by Wage Slave; 15th Oct 2011 at 12:07 pm.

16th Oct 2011, 3:31 am	#66
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Thank you very much for that. These little questions must seem ludicrous to you guys but they are really important to me. I am tempted to spend the £20 or so for the screw in from the site you recommended as I am using the radio five or six hours a day so it is worth it. I'll need to check the hole size but if it is a bit small a bit of filing should solve that and in the very unlikely event it is too big then washers should solve that problem.

17th Oct 2011, 7:55 am	#67
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Well. It turns out my local components store has good quality 350V 47uf and 100uf radials. Total cost about £4.50. Compared to £20 odd including delivery that was a deal. I was going to stuff the old one but realised I needed a 35 mm pipe cutter which I don't have. In the end I found room under the chassis for them and refitted the old capacitor just for looks. All fine and good except it hasn't done anything for the buzzing. Looks like that 54 year old capacitor is still more of less fine! The volume is a tad better I think but the buzzing remains the same. Applies to all wavebands at all frequencies. As you turn the volume control steadily it is very low at low volume and suddenly jumps as does the volume at moderate volume and then drops again as the volume suddenly jumps about two thirds of the way round. Is this motorboating perhaps? I sort of think it is something with the audio stage as it is so volume sensitive and related to sudden jumps in amplification. Any ideas?

17th Oct 2011, 8:34 am	#68
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Re: Philips B3G75U Motorboating is a popping noise that can be slow or fast and your 'buzzing' doesn't sound like motorboating. Check the value of the volume control. If the volume control has a tone-compensating tap on it, check this as well. It's just possible that the control has changed in value. So check across the two outer tags first and you should find that it's within 10 or 15% of stated value. If there is a tap on the control ( a lot of Philips sets did), then check between each outer tag and the tap. The tap will also have tone correction components connected to it so check these as well. If the control has drifted high in value then this can cause the sort of hum you are experiencing especially if the main track also forms the grid leak of the following valve (been there, done that etc)!! If the volume control has an outer metal body, see if connecting this to chassis (if not already done) makes a difference. Also check any screened leads that may be fitted and check that mains feeds (to the switch perhaps) are kept away from the main volume control tags. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

17th Oct 2011, 9:48 am	#69
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Thank you. I'll look at that as soon as possible. Probably at the weekend.

22nd Oct 2011, 7:57 am	#70
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Well, thank you so much Sideband. I think that is my problem. The pot should be 2 Mohms. It measures OK across the two outside tags at 2.25 M. But if I measure from the slider to the end it is a very different story and one which fits the symptoms. It starts off OK at low volume and changes nicely to 2 M or so until it reaches a point where it jumps to 5 or 6. If I leave it, it then drops down to about 4M and remains fairly unstable. Continue turning it and numbers as high as 10M are seen before it slowly settles back to 4M or so. If you keep turning it suddenly drops to .8M, becomes stable and then tapers off nicely and smoothly to zero at the end of the travel. This fits very nicely with the appearance and disappearance of the hum/buzz and changes in the volume of the set. I'm not sure what a tap looks like but I assume it would be an extra tag along with the standard three. In that case, there isn't one. So, I'm hunting for a suitable replacement pot. Am I right in thinking it should be a log type rather than a linear type?

22nd Oct 2011, 8:15 am	#71
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Philips B3G75U Yes, it should be a log pot for a volume control. You may have difficulty sourcing a replacement; such things are getting harder to find in Europe and from your comments in other threads on the lack of interest in aged electronics in your location, a 2M log pot may be tricky to find in Japan. Have you tried cleaning the pot with Servisol switch cleaner or similar? John

22nd Oct 2011, 6:46 pm	#73
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,571	Re: Philips B3G75U Well most volume controls can be dismantled with care. From your measurments, it certainly seems like the control is causing the problem. Fortunately as the track measures OK then it could be an intermittent connection from the contact ring to the slider. You will have to remove the control completely so make a note of the connections. Once the control is out, you should find that the casing of the pot that also holds the switch is held on to the front of the of the pot by bent-over lugs. Turn the spindle of the pot so the switch is in the 'on' position (this just makes it easier to reassemble). It should be possible to carefully bend the lugs up and separate the front part from the casing and switch assembly. You will then clearly see the track and slider with the contact ring. Spray the assembly with switch cleaner (no need to flood it) and work the control a few times to help clean any muck off the slider ring, contact and track. Some people like to apply some petroleum jelly to the track and slider. Check with your meter to see that the control is working correctly. To reassemble, set the slider about halfway round by turning the spindle and simply reverse the dismantling procedure. Make sure the switch operates correctly and refit to the radio. Hopefully you will now have a fully operating control. It takes longer to describe than to actually do the job!! SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

22nd Oct 2011, 8:36 pm	#74
Roy Hexode Join Date: May 2003 Location: Hertfordshire, UK Posts: 258	Re: Philips B3G75U These Philips 2M pots are notorious for failing in this way. The problem is caused by tarnish on the contact ring, not by a failure of the resistive track. Some years ago, I managed to obtain some NOS pots of the correct type for these sets. Although unused, they were just as bad as the originals. If you dismantle and clean the pot as suggested by Sideband, it will be fine. I have attached a couple of photos of an original control from a B3G75U so you can see what needs to be done. It's not at all difficult. Hope this helps, Roy Attached Thumbnails

23rd Oct 2011, 2:14 am	#75
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Right, Thank you very much gentlemen. I'll get on with that today then and report back later.

23rd Oct 2011, 10:14 am	#76
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U And so it was. I had to remove a few components to get it out but out it came and after a good clean it is back in and the radio is working fine now. Thank you all again - A very satisfactory way to spend Sunday.

24th Oct 2011, 1:56 am	#78
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Oh dear. I spoke too soon it seems and I need more advice. I was listening on FM today when it stopped working and I noticed a funny burning smell. The dial light is much brighter than normal and the FM band is completely dead. On MW it still works fine - oddly, perhaps even better than before. The dial light on MW seems dimmer than it was before. Do these symptoms suggest any starting points?

24th Oct 2011, 6:31 am	#79
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U Well, R7 is very nicely roasted and instead of reading 2.2k now manages 112 ohms.

24th Oct 2011, 8:37 am	#80
Wage Slave Hexode Join Date: Sep 2010 Location: Tsu, Japan. Posts: 452	Re: Philips B3G75U So I replaced R7 and the dial lamp went dim again so I was hopeful. However, there wasn't any sound and then I noticed smoke rising from the chassis next to V1. Power off and an inspection reveals that the new resistor has been roasted as well. So, something else is wrong and it is taking R7 out with it. I swapped V1 and V2 as they are the same but that had no effect. I'm a bit lost for ideas now.