Philips b3g75u ferrite bead. - UK Vintage Radio Repair and Restoration Discussion Forum

Kentode · 23rd Nov 2021, 11:43 am

As you can see from the pictures, FB1 (trader sheet 1342) has cracked in two. On my radio it connects the anode of V7, pin 9 to the tag of the dropper section R39.

However the manufacturer's service sheet shows FR43 connecting the cathode of V7 pin 3 to the centre tap, S23 of the output transformer.

I'll be using the trader sheet in any further questions about this radio, so firstly, what is it's purpose? To prevent RF or parasitic oscillation?

Is this eBay listing a suitable replacement. Thanks for reading.

vidjoman · 23rd Nov 2021, 11:48 am

Looks more like a thermistor to me. It’s not a ferrite bead.

Radio Wrangler · 23rd Nov 2021, 12:59 pm

A ferrite bead is, um, bead shaped, and a wire threads straight through its centre hole and out the other side. Ferrite material is brittle and can be cracked, but the wire through its middle isn't going to be broken easily, so whatever is in the photos isn't a classic ferrite bead.

A thermistor for start-up current surge limiting sounds more likely.

David

ms660 · 23rd Nov 2021, 1:14 pm

The ferrite bead fitted to the rectifiers cathode circuit (pin 3) might be in the short length of Yellow sleeving.

Here's another one showing the "thermistor" intact:

https://www.vintage-radio.net/forum/...0&d=1313232382

Some of the component layout doesn't tally up with the Trader or manufactures service data that I have copies of and no thermistor is shown in the said for the rectifier's surge limiter either that I can see....

The two resistors in parallel in the OP's photo look to be the cathode bias resistors for the UL84.

Lawrence

Restoration73 · 23rd Nov 2021, 1:21 pm

The ferrite beads are the two holes type.

Thermistor is VA1010.

Sideband · 23rd Nov 2021, 2:52 pm

Yes agreed, it's a thermistor. Haven't looked at the circuit but I suspect it is surge protection for the rectifier.

poppydog · 23rd Nov 2021, 3:15 pm

On my b3g75u i am currently working on, that appears to be a brimistor to "maintain normal heater current if dial bulb goes", is that definitely a b36g75u chassis ?

poppydog

Kentode · 23rd Nov 2021, 3:22 pm

Right! I was misled by the inaccurate trader sheet.

The picture below shows the ferrite bead, with two holes, in a nice yellow jacket going to pin 3 of the UY85 rectifier.

A quick spin around the forum Search engine and the web shows the thermistor VA1010 to be slightly harder to obtain than a bag of Rocking horse droppings.

Is there a modern equivalent or am I going to have to do a lot of math's to achieve a result?

Restoration73 · 23rd Nov 2021, 7:22 pm

The Radiospares version is TH-6, I have a spare, so send a PM.

Kentode · 25th Nov 2021, 3:25 pm

Thanks for the thermistor Restoration 73, it arrived safely.

It measures 15 Kohms at room temperature and dropped down to less than 10 Kohms when briefly held under a bench light.

I've had a change of plans and will be continuing this Restoration using the Philips service sheets as it has a better layout of the large black capacitors.

Kentode · 25th Nov 2021, 3:30 pm

Forget to include a picture!

23rd Nov 2021, 11:43 am	#1
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,303	Philips b3g75u ferrite bead. As you can see from the pictures, FB1 (trader sheet 1342) has cracked in two. On my radio it connects the anode of V7, pin 9 to the tag of the dropper section R39. However the manufacturer's service sheet shows FR43 connecting the cathode of V7 pin 3 to the centre tap, S23 of the output transformer. I'll be using the trader sheet in any further questions about this radio, so firstly, what is it's purpose? To prevent RF or parasitic oscillation? Is this eBay listing a suitable replacement. Thanks for reading. Attached Thumbnails __________________ Regards, Ken. BVWS member

23rd Nov 2021, 11:48 am	#2
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Philips b3g75u ferrite bead. Looks more like a thermistor to me. It’s not a ferrite bead.

23rd Nov 2021, 12:59 pm	#3
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: Philips b3g75u ferrite bead. A ferrite bead is, um, bead shaped, and a wire threads straight through its centre hole and out the other side. Ferrite material is brittle and can be cracked, but the wire through its middle isn't going to be broken easily, so whatever is in the photos isn't a classic ferrite bead. A thermistor for start-up current surge limiting sounds more likely. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

23rd Nov 2021, 1:14 pm	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Philips b3g75u ferrite bead. The ferrite bead fitted to the rectifiers cathode circuit (pin 3) might be in the short length of Yellow sleeving. Here's another one showing the "thermistor" intact: https://www.vintage-radio.net/forum/...0&d=1313232382 Some of the component layout doesn't tally up with the Trader or manufactures service data that I have copies of and no thermistor is shown in the said for the rectifier's surge limiter either that I can see.... The two resistors in parallel in the OP's photo look to be the cathode bias resistors for the UL84. Lawrence Last edited by ms660; 23rd Nov 2021 at 1:21 pm. Reason: punct.

23rd Nov 2021, 1:21 pm	#5
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Philips b3g75u ferrite bead. The ferrite beads are the two holes type. Thermistor is VA1010.

23rd Nov 2021, 2:52 pm	#6
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Philips b3g75u ferrite bead. Yes agreed, it's a thermistor. Haven't looked at the circuit but I suspect it is surge protection for the rectifier. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

23rd Nov 2021, 3:15 pm	#7
poppydog Banned Join Date: Oct 2015 Location: Cornwall, UK. Posts: 849	Re: Philips b3g75u ferrite bead. On my b3g75u i am currently working on, that appears to be a brimistor to "maintain normal heater current if dial bulb goes", is that definitely a b36g75u chassis ? poppydog

23rd Nov 2021, 3:22 pm	#8
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,303	Re: Philips b3g75u ferrite bead. Right! I was misled by the inaccurate trader sheet. The picture below shows the ferrite bead, with two holes, in a nice yellow jacket going to pin 3 of the UY85 rectifier. A quick spin around the forum Search engine and the web shows the thermistor VA1010 to be slightly harder to obtain than a bag of Rocking horse droppings. Is there a modern equivalent or am I going to have to do a lot of math's to achieve a result? Attached Thumbnails __________________ Regards, Ken. BVWS member

23rd Nov 2021, 7:22 pm	#9
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Philips b3g75u ferrite bead. The Radiospares version is TH-6, I have a spare, so send a PM.

25th Nov 2021, 3:25 pm	#10
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,303	Re: Philips b3g75u ferrite bead. Thanks for the thermistor Restoration 73, it arrived safely. It measures 15 Kohms at room temperature and dropped down to less than 10 Kohms when briefly held under a bench light. I've had a change of plans and will be continuing this Restoration using the Philips service sheets as it has a better layout of the large black capacitors. __________________ Regards, Ken. BVWS member

25th Nov 2021, 3:30 pm	#11
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,303	Re: Philips b3g75u ferrite bead. Forget to include a picture! Attached Thumbnails __________________ Regards, Ken. BVWS member