Emerson Big Miracle

[PJL]

This came with a Philips 472U in an auction house lot I put a cheeky bid on which was 454 miles away. It is in fair condition with what I assume are wrong knobs and a homemade back. There is also a small chunk of the catalin missing but fortunately this is not visible when the bottom cover is on. The chassis however looks in good untouched condition.

I always wondered about the fascination with catalin but at the moment it looks like any other filthy radio. So off to give it a clean and see what the fuss is about!

[Herald1360]

I believe the Catalin fuss is more about bright colours and interesting styling than the material itself. If so, then I suspect your opinion of the Big Miracle is about right.

If I'm wrong, sell it for a tidy profit and get something more interesting to look at!

[PJL]

A clean has made a difference and it should look interesting enough when it's done.

[usradcoll1]

It looks to me, that it never was converted for 230volt mains. It's a typical four valve TRF receiver, made for the US market. IIRC, it's a 1938 model, built around the time when octal-base valves were just coming out.
Catalin was the cheaper alternative to bakelite or wood.
It turned out to be the most valuable to collector's. I only have one in my possession, a 1940 GE AA5, that's nothing special.

[usradcoll1]

Originally Posted by PJL

This came with a Philips 472U in an auction house lot I put a cheeky bid on which was 454 miles away. It is in fair condition with what I assume are wrong knobs and a homemade back. There is also a small chunk of the catalin missing but fortunately this is not visible when the bottom cover is on. The chassis however looks in good untouched condition.

BTW, I failed to mention that the schematic is available from Nostalgia Air.
It's listed under the model BM206?? BM is the basic chassis number.

[vinrads]

May I ask what the cheeky bid was ?
As you probably know Catalin radio's are much collected due to there vibrant colours the under side of your radio is near to to the original colour , if you want to restore it to the original colour you will need to cut the surface back to reveal the original colour ,using medium to fine sand paper then to finish use a cutting compound , I use T cut and loads of elbow grease . good luck with it A very envious Mick

[usradcoll1]

After restoration, never expose the cabinet to bright sunshine. They can discolor very quickly.
I've seen pictures on the internet, where a catalin cabinet had a price sticker on it and subjected to the sunlight. When the sticker was removed, the area where the sticker was, was a lighter color.

[PJL]

I quite like the orange discolouration and in any case it has discoloured around the logo so any attempt to put it back to the original yellow would require a replacement transfer.

It has a replacement electrolytic and a mod to remove the -ve feedback and an extra electrolytic for cathode decoupling. Otherwise the parts are original. The line cord dropper is a plugin extension and looks serviceable although I will use it with a transformer.

P&P was £35 because I asked them to be sent in separate boxes, and that was more than double the auction price.

The knobs will need fabricating as the Bakelite ones look wrong.

[vinrads]

So the auction price was ?
Regarding the colour I suppose it's a personal thing , but I strive to get the case back to how it was when it was made you see more of the original detail when cut back , as has been pointed out when done you need to keep these radios out of the sunlight to avoid the colour fading to to the horrible nicotine colour as many do . This is my personal opinion Mick. ps The logo's are readily available .

[PJL]

£15 for the radios plus auction fees.

[PJL]

I was hoping the R's and C's would be close enough to leave alone, but all paper capacitors are showing very high values indicating leakage and 3 high value resistors have drifted 100%+. The resistors I will run parallel miniature 1/4W's to bring it back to the required value.

I would prefer not to stuff the original capacitors as this is a desirable set. The safest option is to reproduce the capacitors by making replica labels so I can save the originals. I already have to make the missing capacitor so this seems the best option.

I am also interested in why the capacitance measures so high when the leakage current for the 0.1's was only 30uA when wired to a 25V source. I had always assumed that the capacitance increase was a DMM measurement error but I now think it is related to the reduced effective dielectric thickness as it has become part conductive. This would suggest that a leaky capacitor will have an equivalent circuit of the original C in parallel with R and (C in parallel with R and (C....and so on.

[PJL]

For decoupling positions and where the DC leakage is tolerable, it is likely to behave the same as the original capacitor, however, in coupling positions, even when the DC leakage is minimal. the high value capacitance may cause issues such as instability.

[smiler411]

Water has a high value dielectric constant so any moisture will increase capacitance.

[vinrads]

Originally Posted by PJL

£15 for the radios plus auction fees.

I think I feel sick well done with the the purchase ,Mick.