Got it back today

This coil was open.. beats me what it's for. To make the radio work.

Broken Coil:
Image Link

YouTube Video:
http://www.youtube.com/watch?v=HdfrOThXnBY.

You might have to turn it up to hear the radio.
That's the next problem.. it's pretty quiet,
much quieter than when I feed an input into the phono input,
so I still might need help later. but I do have some ideas.

But I feel really good
Thanks to all who helped, it's really appreciated.

The low volume could be due to a number of things.

1. Weak output valve.
2. Dodgey tone control or associated circuitry.
3. Voice coil in the loudspeaker could be poling on the magnet.
4. Dodgey volume potentiometer.

Problem with all of those points is the phono input is fine

What is that coil thing anyway?
It wasn't inside anything, just on it's own bolted to the chassis.
It's just to the right of the first 6D6 (RF) in the schematic.

One thought I have is that the bolt through it was fixed to the chassis,
so the nut going through the coil is supposed to be earthed,
but I couldn't tighten it properly for fear of breaking it again,
so it's bolted loosely, and then superglued, to later be fixed with silicone.

I could make a secure connection to the chassis by other means though.

I do plan to replace the entire valve set.
Got a mate in Victoria that I'm not telling anyone about
Last purchase was 4 NOS tested 6M5 for $10 each

So the sound is okay except for the radio? Add a longer/higher antenna and see what happens.

Yes, I was feeding another radio into the phono before the radio section worked,
so three of the six valves, and audio section must be good.

I'm using the same loop I use for my first valve radio,
and it's good, but I do feel that some experimentation will fix it now.

If audio via the radio is still low it may also require realignment. Turning the screws on the coils the wrong way will lower volume in about half a turn so care will be required.

Ok, .. I will have more questions later, just to gain understanding, even if not required to fix the thing.
I can't understand currently how the tone control could even work.
It's not a potentiomater, but a spinning plate that makes contact
with more and more lugs as it is turned.
That's one example.
I don't need to know that to fix it, but curious.

A lot of radios had stepped switches instead of a variable tone control and such beasts usually had three settings though a few higher prices models had four or five.

That said, if your radio is giving good sound from the phonograph input then the tone control will most likely be working fine.

In this case the tone control (C12) appears to be some kind of variable condenser. Never seen anything quite like it. Got me stumped too!

If the tone control is a rotary switch (you mention more and more lugs) then it will be working by switching in/out more tiny capacitors (say 10-30pf) in increments to alter the modulation in the audio.

A fully variable condensor would be a very expensive way to do it. The other common tone control is a potentiometer that varies the mix between a signal path that goes through an extra capacitor (say 100pf) and a path that doesn't.

Maven

There are no capacitors though, and only two terminals to the whole thing. They can't make capacitors that small, they would have to be as small as our ceramic disc today.

I will have to get a close up shot of it later.

.. then it must be generating variable capacitance within the switching device, or varying the mix with some external capacitor. Internal variance can be done by a lug on the rotor "hovering" over each lug on the stator, creating a simple air capacitance between the two points based on the distance between the two points. No discrete capacitors would be visible. Interested to see pictures.

Maven

We are about to be overrun with kids, so I packed it all up!
but when that is done it will all come out again

I wonder if a coil that isn't shown in the schematic may be a filter for a very strong local station, especially if the coil is in the RF circuit. Something that might have been added by a local serviceman.

It is in the schematic to the right of the leftmost 6D7.
It's not in the component list, but neither are any IF transformers.

I never did try simply shorting it. It couldn't hurt.. it has such low impedance.
But I could never rewind it identical if inclined, I don't know any parameters for it at all.

Things can only get easier now it's working, and as I learn more.
I'm joining the historical wireless society too.
I learned so much at the ham club being able to talk to some older folk.