GEC BC402 receiver.
 

I am very much a novice so I need help I have the above radio and I think the smoothing capacitor has gone on this model it has four connections and it is 50uf+50uf +50uf 275v could any one tell me where I could get hold of one of these please.

Re: Gec bc402
 

Wrong thread? This one is for giving info on where sets and parts can be found AFAIK.

Anyway, you may not find any exact drop in replacement but you may be able to gut and restuff the can with four suitable modern 47uF parts or if function takes priority over form you could simply use four individual capacitors under the chassis leaving the (disconnected) original in place for appearance sake.

Re: Gec bc402
 

What makes you think the cap has failed? Is it hum?.

Re: Gec bc402
 

It is a valve radio. All valves light up but absolutely no sound at all. I think the output transformer is ok

Re: Gec bc402
 

Loudspeaker or its connections? Voltages?

Lawrence.

Re: Gec bc402
 

That hardly points the finger of guilt at the smoothing capacitor! The output transformer COULD be the culprit but you say it's OK. So please tell us what checks you have made and as a result of these checks, what conclusions you have come to.

Voltage checks are the key point here. Tell us what you have measured otherwise we are all guessing. Triple 50uF caps are still available from specialist suppliers but they are not cheap. You don't want to change on guesswork just because you think it might be faulty. Most times, they would fail O/C and cause a very loud hum.

Re: Gec bc402
 

Wrong section anyways for parts needed info.

Lawrence.

Re: Gec bc402
 

When I connect my multy meter to the input terminals on the output transformer I get a crackle noise in speaker. So I assume it is OK. I have replaced all valves with good ones apart from that I don't now where to go I am a novice I assumed then it was the smoothing capacitor =

Re: Gec bc402
 

Certainly not smoothing cap at this point. Needs basic checks for starters. Just take care, lethal voltages.

Re: Gec bc402
 

If the all valve heaters are lit then measure the DC voltage on pin 3 of the rectifiers valve socket first.

Lawrence.

Re: Gec bc402
 

Voltage on pin3 is 547 to 577

Re: Gec bc402
 

Sounds a bit high even without a load, if for instance a feed res was o/c.

Re: Gec bc402
 

If that's DC volts with respect to chassis try again.

Lawrence.

Re: Gec bc402
 

Check what is on either side R36 and if needed the circuit is at the top of this page RHS.

Re: Gec bc402
 

477 voltage on pin 3 DC

Re: Gec bc402
 

R36 reads 560 one end 580 other dcv

Re: Gec bc402
 

I think I've got R36 wrong I have 2 service sheets for this model and R36 is different on both is R36 according to you on smoothing capacitor or on dropper please

Re: Gec bc402
 

Sorry I think I have been reading my meter wrong . 48v on pin3 of rectifier.

Re: Gec bc402
 

Well if you are now reading the meter correctly and you only have 48V on pin 3 look at the circuit diagram and find out what the voltage SHOULD be. Don't try and do these things blind (without a circuit) or you will learn nothing, get frustrated and give up. Firstly get familiar with your meter and learn how to read it.

You'll need to do some more voltage checks. I'm not trying to be unhelpful but the only way to learn, is by doing and looking at the circuit. Clue...the radio needs a LOT more than 48 volts HT to operate. So what does it say on the circuit? Your move.....

I'm looking at the Trader sheet and there is a table showing all voltages.

Re: Gec bc402
 

I am very grateful for your help. I will start again tomorrow. And re check if I am reading things correctly and let you now when I get some decent results

Re: Gec bc402
 

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

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.

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

Re: GEC BC402 receiver.
 

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

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?

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.

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.

Re: GEC BC402 receiver.
 

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

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.

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)?

Re: GEC BC402 receiver.
 

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.

Re: GEC BC402 receiver.
 

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.

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.

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.

Re: GEC BC402 receiver.
 

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.

Re: GEC BC402 receiver.
 

Could even be the smoothing caps pulling the voltage down?

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.