Thanks that makes much more sense

I meant before that I broke the dial cord not the tuning dial.
I'll have to put up a pic when it comes time to fix it.

Bummer,.. power transformer high voltage secondary shorted to the chassis,
the mess can be seen near valve 80 where the power cord enters the chassis.

Image Link

As this happened, I assume, all of the wiring I have replaced in the picture
was heated, and it's insulation came off in places, and also feels a little gooey somehow.

My understanding is the high voltage secondary shorts to the
chassis,
and then the primary heats and shorts some windings,
and then both secondary outputs produce higher voltage.
So it looks like a bit of a disaster for the entire valve set.

How do I know what voltage transformer to replace it with?
I have the schematic, and it seems accurate so far,
but no specifics on transformer output are given.

I do have plate voltage for the rectifier valve is 350 Volts.
Does that mean I'm looking for a 700 Volt centre tapped transformer?

Sometimes the winding voltages are recorded on a bakelite tag strip on the transformer- easy to miss if covered in dust and gunk.

Thanks STC, I haven't removed it to even look yet,
I just know where it is and the wire pairs are obvious.

The surface rust appearance on top, that may have been the restoration.
That's a shame, I'll put a different one on a platform so an
original can go back on top.

This time, if it's feasible, I think I will try to locate the transformer after using a new one.
I have a good idea where to look. Inside Airzone radios of
the early '30s.

The resistance across the high voltage secondary is about 560 Ohms,
so I went ahead and disconnected the transformer, and powered it,
I measured 5 Volts AC and 795 Volts AC.
Something tells me this might be right for this radio.

I will still have to sleeve the wires coming out of it,
some of them are exposed on the chassis side.
Hopefully the sleeve of that new vintage wire can slide off.
Then when it's done, fusing it should remove any doubt.

Nearly done sanding, but I'm kind of afraid to touch it now.

I got one of those stain & varnish in one.. are they any good?

Anyone got an idea what it costs to get stain done professionally?

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Somehow losing confidence when it's coming time to power it :O
It can be better seen here near the label for valve 80
where the secondary shorted to the chassis.

Image Link

It's supposed to be 700, but tests with a multimeter 795 Volts,
but that's unloaded, don't know if that makes a difference.

795 might seem high though it is quite true that the no-load voltage is higher. From here I would suggest running the chassis for about ten minutes, monitoring the voltage. if it remains stable (and if the transformer is not getting warm) it should be safe to start adding valves. I usually add one at a time, starting with the rectifier and working through to the power amplifier.

It wouldn't be game over, but despite my work underneath,
I would hate for the top to have to be modernised.

filament secondary reads spot on 5 Volts.

Thanks for the advice, I will do that.
I have one of those power monitor thingies too.

I will be shaking, it happened for my first one.

I just have to make a 2000 Ohm resistor for the field coil,
but my first try should be today.

After putting the rectifier in and monitoring B+, which will be high because it's unloaded, I turn it off again watching the B+. If the electros have formed up ok and there's no bleed resistors the B+ should drop slowly. If all seems well I'll leave it powered up for 20 minutes or so then turn it off and check for any warm components. The only things that should be hot are the rectifier itself and possibly the choke. A few resistors will be warm and the transformer shouldn't be more than slightly warm. No capacitors should be even the slightest bit warm. Then as Brad suggests add the valves one at a time watching the voltages. Some lucky people have a variac but I made up a dim bulb tester I use during this procedure although it has caught me out a few times chasing low voltages when I've forgotten I was using it!

Is it ok for testing / putting them in one by one, to leave the valve cans off?

four of them have cans.

I am having difficulties with the transformer, incoming in late on this.

Measuring across the transformer can kill modern voltmeters, many are flat out at 400V. The fact that the insulation is goo suggests it was rubber. Turning to goo, and going brittle are its hallmark.

Did I miss something? The fact that the HT grounded, is not giving me evidence that it fried unless the CT burned. My difficulty here is that I would expect the thing to be open both sides? So the open may be at the chassis? not the tranny itself.

What I would suspect is a 385 - 0 - 385 transformer with Zero being the CT tied to chassis. What needs to be seen is the voltages on the plate pins relative to chassis valve removed. (small ones).

I see lots of paper caps in the photo; I do hope that they are gone when you apply DC (put the rectifier back).

Sleeving, perhaps rewiring the leads out, can be simple on some transformers. That one may not be original as I have not yet seen an EMMCO transformer with rubber insulation.

Marc

You're not looking at the latest under chassis picture ;)

Post # 37.

I was testing right across the secondary for that reading,
and although the CT is earthed, the radio was not earthed at the time.

I didn't sort anything out to get under the chassis when it's the right side up,
so I went ahead and tried it with the rectifier 80, and 85,
then all valves in place.
Nothing is hot, the transformer is hardly even warm,
all filaments and globes light up, but the only sound is a squeal.
The squeal changes with the volume control.

Is this about leaving the valve cans off?

No reason to think it's not an original transformer,
the same wiring was all through the radio,
and it would have been silly for someone to do that and replace nothing,
and not fix where the high voltage secondary wire can short
with a bit of movement.

It looks like rubber was there, but was covered in some fabric still.