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Old 20th May 2024, 11:47 am   #1
Keith
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Default Gecophone BC3031 - no info

Hello all,
I've recently acquired the above receiver in restorable condition but have been unable to find any reference to it anywhere. It's not in my copy of Radio Radio or on my BVWS DVD. An internet search returns no finds.
It must date from 1930 or earlier as their is an inscribed plate attached indicating that it was a wedding present in 1930. Any information gratefully received.
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Old 20th May 2024, 12:18 pm   #2
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Default Re: Gecophone BC3031 - no info

Here is a scan from a copy of a small 1929 GEC catalogue.
The set uses the strange 0.8 series of directly heated mains valves. (I have the 2 valve set in this series and am looking for a D.08 valve which was missing from my set, very rare!)
Mike.
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Old 20th May 2024, 2:14 pm   #3
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Default Re: Gecophone BC3031 - no info

Thanks Mike,
From your catalogue page it was clearly quite an expensive set back in 1929. I can't read the front end valve numbers but the output is a PT625 and the rectifier is a FW4/500. Sadly, pitch has exuded from the top of the mains transformer can so that doesn't bode well forbringing it back to life...
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Old 20th May 2024, 5:42 pm   #4
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Default Re: Gecophone BC3031 - no info

The transformer on the 2 valve BC3020 set I have was getting very hot when tested with the valves removed so the transformers on this range of sets may be problematical. I haven't done anything more with the set as one of the tuning coils also needs rewinding and, not having a D.08 there isn't much point in doing anything at the moment.
If the BC3031 has the original transformer, the only valves that could be used in the screen grid and detector stages would be the S.08 and D,08 as the filament winding is only 0.8 volt (0.8 amp for the S.08 and 1.6 amp for the D.08).
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Old 21st May 2024, 2:42 pm   #5
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Default Re: Gecophone BC3031 - no info

Keith,

I don't know what the difference is between the 3030 and the 3031 but it looks the same as the 3030 I had a long time ago. I traced out the circuit of the 3030 and I've attached the PDF, hopefully it might be of some use.

Regards
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Old 21st May 2024, 5:24 pm   #6
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Default Re: Gecophone BC3031 - no info

Hi Peter,

Thank you so much for the circuit diagram of the 3030. Now it all starts to make sense. It looks pretty much the same as what I'm seeing in the 3031. Obviously the design is very different to the 3020, which is something of a relief as the rare .8 valves could have been a show stopper.

The mains transformer runs cold with no valves plugged in so not sure what caused the obvious past overheating - I need to investigate smoothing capacitors etc.

Anyway, I'll let you know how I get on.

Regards,
Keith
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Old 22nd May 2024, 12:12 pm   #7
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Default Re: Gecophone BC3031 - no info

Looking at the circuit diagram, the reason for the evident transformer overheating was probably as a result of a PO fitting the FW4/500 (3A filament). I'm now scratching around the correct U10 or equivalent.

Still slightly confused about the set as the front end valveholders seem to have less than 4 volts between pins 3 and 4. The o/p valve has a 6V filament supply so the PT625 seems correct. Both detector and o/p have side contact connections, the RF stage being a ground (for the cathode?) and the o/p taken to HT (for G2). The dial lamp bulb fitted was a 0.8-0.9V MES (now o/c). It seems to wired across the o/p valve filament as in the circuit.
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Old 23rd May 2024, 11:38 am   #8
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Default Re: Gecophone BC3031 - no info

It seems there must have been at least 2 versions of this set, the earlier with the 0.8 volt valves, the next version with the more conventional ones, the 0.8 volt valves don't seem to have been a great success!
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Old 23rd May 2024, 3:28 pm   #9
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Default Re: Gecophone BC3031 - no info

I reckon you're right, Mike. Having now got the chassis out it's clear the phantom bodger has been in there - can't yet see why he felt the need to use an alternative arrangement for the heaters of the front end valves. There seems to be about 0.7VAC on the disconnected winding. Maybe he was trying to give the valves an end of life boost? Nothing in the AVO valve tester data on S.8 or D.8 so it'll be suck it and see!
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Old 4th Jun 2024, 7:18 am   #10
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Default Re: Gecophone BC3031 - no info

Keith, I managed to find a couple of pictures of the chassis of the BC3030 which might be of some use so I've put them into the attached PDF
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Old 4th Jun 2024, 11:55 am   #11
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Default Re: Gecophone BC3031 - no info

Thanks Peter,
From the underside view it looks like the 3030 used a common heater voltage (presumably 4V) for the front end valves. My 3031 uses 4V for the detector and 0.8V for the screened grid (S0.8). So altogether 4 different heater/filament supplies including the rectifier!
I guess that a previous owner hadn't heard of 0.8V valve (neither had !) so thought that the winding was duff. Hence the diode to get 2V from the 4V winding. Luckily the S0.8 still has an intact heater - whether it still has emission I have yet to find out.
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Old 4th Jun 2024, 4:49 pm   #12
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Default Re: Gecophone BC3031 - no info

If you want to test the Point 8 valve this is a link to the Marconi valve manual of 1928 https://www.6v6.co.uk/vcomp/manuals/...ual%201928.pdf which lists the valve characteristics. From these it should be possible to test the valve on your AVO, although you might have to supply the heater from an external supply or use the 0.625V setting?
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Old 4th Jun 2024, 7:12 pm   #13
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Default Re: Gecophone BC3031 - no info

Thanks again Peter,


What a great publication. I love the way they show diagrams of the electrode structures. I may well need to test the S.8 as I now have the receiver working but the SG stage is attenuating rather than amplifying. Could be an o/c coil I guess or something else that can be fixed easily. Hopefully not the S.8!
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