GECoPhone BC3235: Voltages

[HowardB]

Thanks Graham.
Here's a close up of the box...
and there's another pic at #17.

Howard

[Station X]

Thanks for the picture.

Would it be easier to gain access from the bottom where the leads attach? You'll need to remove the box from the chassis in any case.

[HowardB]

Unfortunately not, the bottom looks even harder to access.
The leads attach to a terminal connector at the top - see photo.

The capacitor box is completely closed on all 6 sides.
The aerial box is actually a cover. It has 5 sides, the bottom is open, so when it is unscrewed from the chassis it lifts off to reveal the coils.

I think I have a strategy now - I'll do the easy bits first, like cleaning the wave-change switch, replacing the accessible caps under the chassis and see what effect that has.
I'll only tackle the capacitor box if absolutely necessary.

Howard

[Station X]

I see your dilemma. Having prised apart the start of the seam you may be able to work your way round with a big soldering iron peel the seam as you go.

You may be able to test the caps from outside the can via the connection points. Electrical leakage is the biggest problem and needs to be checked at the full working voltage.

[HowardB]

Update:

Condenser-Pack

I borrowed a high powered soldering iron and managed to remove the top of the box.
Chipped away at the pitch but didn't want to go too far in case I damaged something - see photo.

I disconnected the external wires at Pin-1 & Pin-2 and checked the 1uF:
It measured 1.243uF, VLOS 0.8%, ESR=0, surprisingly good for a 90-year-old cap.
I also measured the voltage on the pins which showed a large voltage difference across each cap, so I assume they are not leaking.

With these results perhaps I should forget about replacing the 4 caps and just leave the Condenser-Pack as it is?


Speaker

I connected my 1928 BTH Loudspeaker (moving iron, model E form C, 1500-ohms) and was immediately blown away by the difference in volume and tone.
The original speaker is pretty quiet, virtually a whisper whereas the BTH is almost too loud. The difference is night and day. I also tried a modern 8 ohm speaker via an output transformer, and this was equally as loud.

So - should I maintain originality and stick with the whispering speaker or replace it with a new one that actually works?

Is the original speaker (see photo) totally knackered or is there any easy fix to bring it back to life?

Howard

[Ed_Dinning]

Hi Howard, despite the measurements on the cap block they WILL BE leaky and defective and should be replaced.

The quiet speaker sounds as if the coil is OK, but the rubber suspension pieces will have hardened. These are normally easy to replace (see forum threads) and it will sound good again

Ed

[HowardB]

Hi Ed,

Given that the radio was already working, I was sorely tempted to leave it alone, but you convinced me to push ahead with the replacement.

The condenser-pack contained 4 capacitors, arranged as a solid block of waxy paper and foil, all crammed into the metal box then covered with black pitch.

The pitch was brittle and could be broken up piece by piece but the capacitor block was much harder to remove. In the end, I used a drill almost as a blender to break the block up into capacitor soup! The soup was then extracted with a vacuum cleaner. The whole process was slow, laborious and very messy.

In retrospect, I could have just removed the whole box and mounted the replacement caps directly onto the chassis using a terminal strip. This would have altered the appearance of the radio but would have been a whole lot easier. Anyhow - the new caps are in place - see photo, and the radio still works, so I'm pleased with that.

I can now focus on the speaker; The outer ring has some tears that could be repaired but I can't believe it would make that much difference. The speaker is basically lacking in power - the others I tried are orders of magnitude louder. Any ideas welcome.

Howard

[Cobaltblue]

I have found with early speakers that if the coils are OK then the magnets seem to be weak or sometimes both!

On a few of my Horn speakers I have used small neodymium magnets attached to the existing magnets and that massively improves the performance.

Also worth checking that the driver mechanism isn't stuck on the pole pieces.

It would be nice to keep it as original as possible since you have made so much effort with the capacitor Box.

Cheers

Mike T

[HowardB]

Ha - great minds think alike - I already tried placing some very small neodymium magnets onto the existing magnets but it didn't seem to do anything. Not sure how to check if the driver mechanism is stuck. Can I just squirt WD40 into it?

Howard

[HowardB]

With nothing to lose, I tried some WD40 into what I believed was the voice coil section.
Gave it a few minutes to soak in and then wiggled the centre of the speaker.
Pushed the centre in a bit and there was a definite 'click', as though it was going back into place.
Can you believe it - the speaker is now working properly - much much louder!

The cone is still in a sorry state so might have a go at replacing the perished outer ring.

Howard

[Ed_Dinning]

Hi Howard, tissue and PVA glue should sort the cone

Ed

[HowardB]

The attached PDF details the replacement of the capacitors in the Condenser-Pack.
Hope this is useful to somebody in the future.

Howard

[HowardB]

Update:

As you may remember, the speaker on the GECoPHONE 3235 was in a terrible state, with rips and tears in the paper cone and the outer ring being more or less totally perished.

I have now repaired the cone using tissue paper and replaced the outer suspension ring with a part sourced on eBay for around £4. I used Copydex glue for both the cone and the ring and found this to work perfectly as it is rubber-based. The whole job was fairly easy to do.

Overall, I'm very happy with the result. The speaker has been saved. It's not Hi-Fi but it works well enough. The radio is now loud and clear without too much distortion. Amazing for a primitive 1930 speaker.

Howard

[ChasHeater]

Hi Howard, I have followed your restoration with interest as I have one of these. Mine was in a worst state cosmetically having had water damage to the case and the Bakelite grill was missing. I have fabricated a new grill and restored the case. As yet I have not attempted to restore the electronics, but it does work, though poorly. I made the decision to remove and substitute the speaker (mine is in good order) with a modern unit and installed a small receiver/ amplifier and use it every day - it’s got the look! I should add that my conversation is done out of site so as not to damage the original radio. I might get round to fixing it properly one day. Regards, Charlie

[HowardB]

Hi Charlie,

I bet it was quite a job to refabricate that fancy grill. I'd be interested to know how you did it and see the result. Let me know If you ever want to sell the speaker or any of the other bits.

I've finally finished my one. Here's a picture...

Howard

[ChasHeater]

Hi Howard, See attached for my effort.

[vinrads]

Fantastic job Howard, well done indeed , Mick.