Hi All. Would anyone know where I can purchase an IF Filter rated 17.5 ohms up to 60 ohms for a Radiola 540-MA. I have attached a photo for ID. I did find them on a web page but cannot find the site anymore.

Thanks.
Hammer_651

Photo uploaded.

If the coils have continuity, it looks to be repairable.

It has not unraveled, the wax has stopped that. So, having had the experience of coils being ratatouille, I am saying don't panic yet.

You need to look carefully at the wax, to give a clue as to where the wire was. See if you can find the origin of the top coils finishing wind.

The bottom one is obvious, so that will tell you which tail, connects to the next and the length of the wire is also a clue. You may need to splice in wire. Nice fiddly job, I use a scalpel to scrape off insulation.

The last one I did I ended up melting the wax off, but I see no need for that here.

Marc

Where is that coil in the circuit?

It does not appear to be adjustable, is it just an RFC in the output of the detector?

If so it could be replaced with a modern part, such as a readily available 330uH or thereabouts axial choke. It's about the size if a half-watt resistor. Example:

https://au.element14.com/bourns/78f331j-rc/inductor-330uh-5-0-1a-axial/dp/2858881

Hard to believe, but yes, it'll do the same thing!

Most radios don't have an IF filter, and the radio will work perfectly well without it. I believe its function is to ensure stability at the lower end of the MW band.

If you can't work out which wires to join, I'd do as Ian Robertson suggested.

The coil looks very much like the IF filter in AWA 427MA Champion. I had one of these open circuit which was fixed by melting the wax off it in the oven (more heavily encapsulated than yours), and doing the fiddly fix as Marc describes. Luckily mine only had one break.
This sort of fix is why you have as many visual aids as you can get, and as many sorts of tweezers as you can get!

Keep the wax if you can - it has a higher melting point than bees wax and is handy for repairs on RF coils and transformers.

Its the series resonant trap in the grid circuit of the convertor.
My AWA's don't have it.

Its "L1" on the circuit with "C1" as the resonate on the short wave models.
Not sure but the reason may have been the tuning range covered the IF frequencies or harmonics of the IF.
That would make whistles while tuning and the L/C would trap them out.

Funny thing it would help with the problem nowadays with the switch mode street lamps emitting around 450Kc and drowning out weak signals!

Leave it out, or fix it, but its not crucial.

Fred.

Hi all and thanks for your expertise.

Ian, The filter is before the first Aerial Coil (540-1600Kc/s L2-L3) and is not adjustable. One end of the coil is connected to the primary of the 1st aerial coil and has a 50pF in series then grounded, it is also separate from the other coils in the chassis. I also believe it's to filler to out any unwanted frequencies before the 1st aerial coil. If I used the choke, will it require the capacitor too?

I forgot to add this question in the post, what type of wax/resin should I replace on the IF Filter and on the other coils. The other coils, which have insulation damage, have a black type resin on them which is cracked and some missing. I need to cover them.
Thanks again all.
Paul.
Hammer_651

The last few coils which I have had cause to re-insulate: CRC make a seal coat in two colours.

"Urethane Seal Coat" Motor & Generator winding coating insulator. Code 2044. See their website for more data.

The L1 circuit is grounded in SW, and only does something in MW. A coil and capacitor in series will short out a particular frequency (in this case 455kHz), following from known calculations. It isn't adjustable because only one frequency is involved and it's not particularly crucial.

The idea, I think, is that radiation from the unshielded 6BE6 and 6BA6 anodes could in theory radiate back into the front-end and possibly cause instability. The L1/C1 combination is there to get rid of that possibility.

But, look at almost every other radio and you'll see that such a filter isn't there, which shows it isn't that important.

Yes, so your filter is a series tuned circuit that's intended to trap out the IF frequency of 455kHz (presumably).

A 330uH fixed inductor as I posed a link to will need 370pF in series with it to make a 455kHz trap. 330pF with 39pF in parallel gets you very close.

If you are looking for a really permanent solution for wax and bitumen sealed windings, consider the technique we use for renovating TV line transformers of the wax and paper variety. Boil in turps, followed by a soak in polyurethane marine lacquer.
Very effective and very permanent, the polyurethane will probably last 100 years!

Boil in turps

In case it needs to be said: no naked flame.

Absolutely. I do normally point that out.

For my first effort I used the BBQ side burner, with a fire extinguisher at the ready. I needed it!

I now use an electric slow cooker, OUTSIDE on a long extension lead!

Where there is no bitumen, just wax, Prepsol does a great job, at room temperature.

http://www.earlytelevision.org/saving_flyback_transformers.html