Hello,
I was recently given this radio to recap and restore to working order but
I'm a little out of my league on finding a replacement on this one.
All I know is the speaker is a Rola 5C:

https://www.radiomuseum.org/r/rola_aus_5_loudspeaker_5c_with_f87_cone.html

2.5W, 3.7Ohms, 5000 load impedance on the primary.
I watched David Tipton's video that explains it's a 36.8:1 ratio.

https://www.youtube.com/watch?v=X12Cz3-jB5Q

I'm looking at the universal transformer he was using.
Anybody got any other ideas for another replacement?

Thankyou, Rick

Vintage Transformers in Victoria.
He has re wired Kriesler Rola transformers for me back to spec.
Excellent job and I was very happy with the Transformers and the cost,
Look him up on the net.


Pete

Hi Pete!

Thanks for the quick response and the solid information.
Will follow him up.
Cheers and Thankyou again, Rick

edit: If this is the guy, looks like he is 'out of action'...

http://www.transformerrewind.com.au/

His contact details are on the Services page, here: https://vintage-radio.com.au/default.aspx?id=20#VIC

Hi GTC,
Why didn't I think of that?
Thankyou Kindly,

Rick

This is definitely and easily available and will work just fine (despite not being core gapped):

https://www.jaycar.com.au/5w-line-speaker-transformer/p/MM1900

You might want to try the different taps to see which gives you the best result.

Hi Ian,
That's mighty cheap too.
Would that also be suitable with a 3.7 Ohm speaker?
Thanks, Rick

Just a matter of choosing the right tap to match the speaker to the valve. Pick the one that gives you the loudest sound without distortion.

This is known as the Eclectic Empiricist method! You use it when you don't have all the data....

Yeah Ok, Thanks.....
My other concern is, the schematic for it has the B+ run straight into on side of the primary output transformer,
and the other side which makes sense, goes to plate of the 6V6.
Would the transformer you suggested still be appropriate?
Thanks for taking the time, I appreciate it!
Rick

Yes.

Primary goes to 6V6 plate and B+.

If there is a negative feedback connection you may have to reverse B+ and Plate to get the feedback the right way around.

Some radios have B+ connected to the core of the transformer with the transformer insulated from the speaker / chassis. This is not necessary with modern transformers.

Okay!
Thanks so much for your help.
I'll order it and see how I go!
Cheers,
Rick

These transformers are not really designed to have a DC voltage passing through the primary, it causes core magnetisation and slightly increased distortion. Ideally they need to be "gapped".

If you want to waste some time you can pull the core out and re-stack the E's and I's so they are separate. Then put them back in the bobbin and bracket with a strip of sellotape between the E and the I stacks. Bend the tabs tight.

Depending on how hard the 6V6 is biassed on, you might get a couple of dB improvement, but I doubt you'll hear the difference.

Ah right,
That makes sense.
I'm not sure I'm that keen pulling out the core and 'fiddling about' haha.
The project is only to have it running and running safely.
Somebody 'played' around with the output transformer before as the wiring didn't fit.
Still, it was still defunct.
The coupling cap was toasted and black!

A fun project it's been so far.
All recapped, the resistors all seemed to be in tolerance surprisingly considering it's from 1948.
Just ordered a new 'vintage' style 3 prong cable, a fuse, knob felts and cloth wire.
The case is a little messed up, but gonna try to lightly sand and buff the exterior,
to which I've never attempted before.
I hear Brasso is the thing but I was going to try and use 'PlastX'....?
It's what I have on hand.
I've watched a tonne of video's for inspiration....
I'm doing a bit at a time

I can only 'mess' it up...



Cheers, Rick

Oh dear, I've got another question about the Jaycar transformer....
It says it's 'designed to tap 100V'.
I refer to the David Tipton video I mentioned above at the 5:58 mark where the Voltage hits 222V on start
to test his transformer.
Question, wouldn't this Jaycar transformer to small to handle that voltage?

Thanks, Rick

No it's OK.

What it's for is for 100 volt line PA systems. The idea is the PA amplifier drives the line to 100 volts RMS at max output. That's 282 volts peak to peak, more than you'll get from a 6V6.

With such a PA system you connect speakers via transformers across the line, the total of the tap settings you use cannot exceed the power rating of the amplifier.