LF transformer Marconiphone 282 wanted

[Geri]

Dear forum members,
 
For my Marconiphone 282 I am looking for the LF transformer complete with band filter. Both are housed in one round steel housing. Unfortunately I am not able to post a picture of this unit to this thread. This LF unit consists the band filter C6 and L11 and the LF transformer L12 and L13. According to another schematic, which I found on the internet, the LF transformer is called TR1. The coil L11 of the band filter is defective. This complete chassis was also used in the HMV 148, and the Columbia 1008 radios.
The radio still works, but the low tones remain behind, because the LF signal can now only reach the LF transformer via C6 (500pF).
If you don't want to sell the transformer unit as a separate part, I'll also be happy to take over an entire chassis or so, provided the coil unit is okay.
Unit readings approximately: L11 plus L12 = 1500 and L11 plus L13 = 4250 Ω.
I have already experimented with other LF transformers, but without the filter the sound is not nicely in the lower frequency range. I also would like to keep the radio original, so no strange components. Who can help me with this?
 
Kind regards, Geri

[Ed_Dinning]

Hi Geri, these transformers and related parts can be a great problem in old sets due to the fine wire and paper insulation used. This leads to green spot corrosion of the transformer and inductor windings. The best solution is a complete rewind. This can be quite expensive due to the high number of turns of fine wire needed.
If it is bitumen potted that adds a further complication as it is messy to remove

I wish you luck in finding a replacement, but even an unused one may be in a poor condition after all these years

Cheers, Ed

[Geri]

Hi Ed,
The whole coilset is indeed cast in a kind of rubbery bitumen, which is still not completely hard. And as you mentioned, I'm also afraid that not much will be left of the coils if I try to remove them from the bitumen.
Somewhere, such a coil set in good condition will still be on a shelf. I'm desperately looking for that shelf now. That shelf will probably be found in the UK sooner, because the radio is made in your country and shurely more have been sold than on the continent. I love that radio for its beautiful design and its great performing simple technique.
Sincerely, Geri

[Ed_Dinning]

Hi Geri, a picture may help jog memories
They can usually be extracted from their cans by warming in an oven at 100C for a while, but beware the smell of hot bitumen
Once our of the can and cool, put in the freezer and when cold the remaining bitumen can be carefully chipped off the assembly. These assemblies are fairly robust and were self supporting before being potted

Ed

[Geri]

Thanks Ed for the suggestion!
If all goes well, there is now an image and a schematic representation of the LF transformer with this Thread.
The LF unit contains C6, L11, L12 and L13.
I hope this triggers someone now.

Geri


   

   

[Ed_Dinning]

Hi Geri, that should not be much of a problem; note the the paint on the can may discolour and you will need to re-spray

I think I did a Marconi one like this some years ago, but it had a centre tapped winding not a seperate choke

Ed