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Old 29th Jul 2015, 7:16 pm   #1
loveoldradios
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Default GEC BC401 Valve Radio Tips

Hi I have just purchased a GEC BC401 valve radio does anybody have any tips on this model?
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Old 29th Jul 2015, 8:21 pm   #2
Cobaltblue
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Default Re: GEC BC401 Valve Radio Tips

Welcome to the forum

This set is pretty late into the valve era and is an AC DC set with a printed circuit board.

You can obtain the service data here

It would be good to know your level of experience but you should certainly change the output valve grid coupling capacitor C17 on the manufacturers service data.

Cheers

Mike T
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Old 29th Jul 2015, 8:32 pm   #3
TonyDuell
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Default Re: GEC BC401 Valve Radio Tips

I think it is worth pointing out 2 features of the AC/DC design. The name comes from the fact that it will operate on either AC or DC mains, which of course means there is no mains transformer (this would only work on AC mains).

The first feature is that the heaters (filaments if you like, but that is not the right term for these valves) are in series. This 'heater chain' is wired in series with a suitable resistor and connected across the mains. Therefore if the heater of any valve burns out all the heaters stop working.

The second is more important. The high voltage (normally called HT+) for the anodes of the valves is obtained by half-wave rectifying the mains. The rectifier is always in the positive side of the suppy, and if you think about the circuit this means the negative side -- the radio chassis normally -- is connected directly to one side of the mains. It should be the neutral wire, but never assume this!. This means that just about everything in the radio is connected to the mains making it a potential shock hazard. And you can't just clip a 'scope anywhere you like as the 'scope ground lead is most likely connected to mains earth.

If you have to work on such a set when it is powered up, or if you want to examine waveforms with a 'scope then you should power the set from a double-wound isolating transformer.
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Old 29th Jul 2015, 9:26 pm   #4
Ed_Dinning
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Default Re: GEC BC401 Valve Radio Tips

Hi feel free to contact me by PM (private message) if you need any assistance as I am quite local.

Ed
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Old 30th Jul 2015, 8:42 pm   #5
loveoldradios
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Default Re: GEC BC401 Valve Radio Tips

Thanks.
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