GEC BC402 receiver. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Sideband · 18th Jun 2021, 10:46 pm

Mods, can this thread be moved to the correct section please?

Station X · 19th Jun 2021, 8:20 am

If you think a post is in the wrong section please use the red triangle button to report it. It'll get quicker attention that way.

Thread moved to VRD as it's become a repair thread.

"Where can I get.....?" type threads are OK in SP&SIW. After all many threads in that section get replies like "Available from supplier X".

Back on topic please.

Dorian27 · 19th Jun 2021, 11:56 am

OK I have taken readings from pin 3 on 3 different meters and what I get with all 3 is the same when first radio is switched on I get 119v dc as the valve warms it goes down to. Point 785v dc. Tried a valve new same reading. Can't tell you any more. Hope this helps

Station X · 19th Jun 2021, 12:16 pm

Are you saying that the reading starts at 119VDC then drops to 0.785VDC?

Station X · 19th Jun 2021, 12:30 pm

Try disconnecting one end of R35 (500R) which will leave just the reservoir section of the smoothing caps connected. What's the reading like then?

Dorian27 · 19th Jun 2021, 12:50 pm

I have used 3 diffrent meters and the readings i got on pin 3 is on radio switch on i get 119v dc as the valve warms it goes down to point 785 i then replaced the valve with good working one and same reading hope this helps.

Dorian27 · 19th Jun 2021, 12:53 pm

Sorry I seemed to have posted the same reply twice I will take new reading later thank you very much for much needed help.

Dorian27 · 19th Jun 2021, 1:24 pm

Well the reading with R35 disconnected is 140v dc and rising as valve warms.

Dorian27 · 19th Jun 2021, 1:32 pm

I believe according to the service sheet it should be around 175v dc I left it on a while without resistor connected it is now 180v so I've turned it off.

Station X · 19th Jun 2021, 1:34 pm

If the rectifier is working correctly and C58 is good the reading should rise to 240VDC or more.

What AC voltage do you see on the rectifier's heater (between pins 4 and 5)?

Station X · 19th Jun 2021, 1:37 pm

Quote:

Originally Posted by Dorian27

I believe according to the service sheet it should be around 175v dc I left it on a while without resistor connected it is now 180v so I've turned it off.

I don't know where you're getting your figures from, but the two service sheets I've looked at show the pin 3 reading as being 235-238VDC.

ms660 · 19th Jun 2021, 1:41 pm

Quote:

Originally Posted by Dorian27

Well the reading with R35 disconnected is 140v dc and rising as valve warms.

Under normal circumstances with R35 disconnected that voltage should rise to the peak value of your mains supply voltage, the peak value of the mains supply voltage is easy to calculate, it's the mains voltage (RMS) multiplied by 1.414, for instance if your mains voltage was 240 volts AC then the peak voltage would be 240*1.414 which would be 339 volts peak AC, the voltage across the reservoir capacitor (C58) would rise to that voltage but that voltage would be DC.

That's one of those things that should be learned early on and never forgotten along with Ohms Law and the fact that all circuits are potential dividers.

Lawrence.

Dorian27 · 19th Jun 2021, 3:23 pm

Yes you are correct on pin voltage it is 235 to 238 dc. I don't now where I got 175 from. I went up to 180dc when I turned off as I thout it was 175 and did not want to do any more damage. What do I do now do I let it on to rise or not. Does this mean by disconnecting the resistor that the resistor is faulty or something else.

Station X · 19th Jun 2021, 3:40 pm

See how high the voltage rises, but make sure the capacitor doesn't get hot. Turn off the set and disconnect the mains periodically then feel how hot the cap is. Remember that it will retain a charge for some time.

This test is to show whether the rectifier and reservoir cap are OK.

The resistor doesn't come into it and is easily checked with a meter on ohms range.

Sideband · 19th Jun 2021, 4:00 pm

Quote:

Originally Posted by Dorian27

I believe according to the service sheet it should be around 175v dc I left it on a while without resistor connected it is now 180v so I've turned it off.

Could you please say which service sheet you are working from? Nowhere does it say that the voltage on pin 3 of the rectifier is 175V.

HamishBoxer · 19th Jun 2021, 5:05 pm

Could even be the smoothing caps pulling the voltage down?

Station X · 19th Jun 2021, 5:55 pm

Could be, but we haven't got as far as testing the rectifier and reservoir capacitor yet. We're waiting for the OP to report test results.

18th Jun 2021, 10:46 pm	#21
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,572	Re: Gec bc402 Mods, can this thread be moved to the correct section please? __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

19th Jun 2021, 8:20 am	#22
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. If you think a post is in the wrong section please use the red triangle button to report it. It'll get quicker attention that way. Thread moved to VRD as it's become a repair thread. "Where can I get.....?" type threads are OK in SP&SIW. After all many threads in that section get replies like "Available from supplier X". Back on topic please. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jun 2021, 11:56 am	#23
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. OK I have taken readings from pin 3 on 3 different meters and what I get with all 3 is the same when first radio is switched on I get 119v dc as the valve warms it goes down to. Point 785v dc. Tried a valve new same reading. Can't tell you any more. Hope this helps

19th Jun 2021, 12:16 pm	#24
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. Are you saying that the reading starts at 119VDC then drops to 0.785VDC? Attached Thumbnails __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jun 2021, 12:30 pm	#25
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. Try disconnecting one end of R35 (500R) which will leave just the reservoir section of the smoothing caps connected. What's the reading like then? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jun 2021, 12:50 pm	#26
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. I have used 3 diffrent meters and the readings i got on pin 3 is on radio switch on i get 119v dc as the valve warms it goes down to point 785 i then replaced the valve with good working one and same reading hope this helps.

19th Jun 2021, 12:53 pm	#27
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. Sorry I seemed to have posted the same reply twice I will take new reading later thank you very much for much needed help.

19th Jun 2021, 1:24 pm	#28
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. Well the reading with R35 disconnected is 140v dc and rising as valve warms.

19th Jun 2021, 1:32 pm	#29
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. I believe according to the service sheet it should be around 175v dc I left it on a while without resistor connected it is now 180v so I've turned it off.

19th Jun 2021, 1:34 pm	#30
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. If the rectifier is working correctly and C58 is good the reading should rise to 240VDC or more. What AC voltage do you see on the rectifier's heater (between pins 4 and 5)? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jun 2021, 3:23 pm	#33
Dorian27 Heptode Join Date: Jun 2018 Location: Carmarthenshire, Wales, UK. Posts: 566	Re: GEC BC402 receiver. Yes you are correct on pin voltage it is 235 to 238 dc. I don't now where I got 175 from. I went up to 180dc when I turned off as I thout it was 175 and did not want to do any more damage. What do I do now do I let it on to rise or not. Does this mean by disconnecting the resistor that the resistor is faulty or something else.

19th Jun 2021, 3:40 pm	#34
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. See how high the voltage rises, but make sure the capacitor doesn't get hot. Turn off the set and disconnect the mains periodically then feel how hot the cap is. Remember that it will retain a charge for some time. This test is to show whether the rectifier and reservoir cap are OK. The resistor doesn't come into it and is easily checked with a meter on ohms range. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jun 2021, 5:05 pm	#36
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: GEC BC402 receiver. Could even be the smoothing caps pulling the voltage down? __________________ G8JET BVWS Archivist and Member V.M.A.R.S

19th Jun 2021, 5:55 pm	#37
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: GEC BC402 receiver. Could be, but we haven't got as far as testing the rectifier and reservoir capacitor yet. We're waiting for the OP to report test results. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.