Scratch-Build an All American 5 Superhet Radio

[usradcoll1]

Originally Posted by regenfreak

the transformer is British made rated at 200W, isolation step transformer(link below), it looks high quality and beefy. Even it is idle and housed in good ventilation, it is "scorching" to touch. The idle consumption is 17W measured with a power meter. It gets very hot after 30 minutes of running a 22W AA5 radio. I am surprised by the large hysteresis loss and I am worried it is a fire hazard because on one occasion I forgot to unplug it overnight and it was burning hot.

https://www.ebay.co.uk/itm/MV-200-P1...oAAOSwIbFdLEG2

I have a 150W Chinese made 240V-240V isolation transformer, it is not hot idle or under load.

PS. Many commercial 240v to 110v convertors have autotransformers and not isolated from the mains.

I bought a travel step down transformer that is equipped with a BS1323 plug. it is still a screw terminal plug, so it must be an older issue. It also has a 13 amp fuse. It's an autotransformer type, so there is no isolation.
I never left it on to see if it runs hot with no load.
Always interested, Dave USradcoll1.

[regenfreak]

I bought a travel step down transformer that is equipped with a BS1323 plug. it is still a screw terminal plug, so it must be an older issue. It also has a 13 amp fuse. It's an autotransformer type, so there is no isolation.
I never left it on to see if it runs hot with no load.
Always interested, Dave USradcoll1.

Usually the manufacturers save iron by using autotransformers for most low-end stepdown convertors. For 110V vintage radio restoration and experiments, I would not compromise safety and opt for 240V-110V isolation transformer even I have to pay more.

The manufacturer has written back saying it is 4W per kg loss with no load, rated 120C for the core materials breakdown. It is too hot to touch after 90 minutes no-load without housing, like a mini radiator. So I can't figure out whether it is normal or it has shorted turns

[usradcoll1]

Getting back to basics.
I've been reading this thread with a lot of interest!
It's been ages since I built an AA5. A friend bought three AA5 kits from the community college for a dollar each, as they were no longer teaching radio-TV repair. She said to assemble two for her sons and I can keep the remaining one.
It was more pleasure than work and both worked flawlessly. I still didn't build the remaining one, it's stored somewhere!
Dave, USradcoll1

The "ballast tube" in post 5 looks like a simple resistor not a constant (ish) current baretter.

[regenfreak]

The "ballast tube" in post 5 looks like a simple resistor not a constant (ish) current baretter.

It looks like the barrel of an air-cooled Browning machine gun.

It's been ages since I built an AA5. A friend bought three AA5 kits from the community college for a dollar each, as they were no longer teaching radio-TV repair. She said to assemble two for her sons and I can keep the remaining one.
It was more pleasure than work and both worked flawlessly. I still didn't build the remaining one, it's stored somewhere!

For sure, you have a hidden, time-warp treasure somewhere in your house. An objective has an extra significance if it can bring back memories of youth yearning for knowledge.

In the Great Pandemic of 2020, I have been reading an article about the introduction of Philco Model 70 Cathedral superhet in the Great Depression which was sold for $49.95. Assuming it was 1931, it would cost $848 today money using the inflation calculator:

https://www.wshu.org/post/radio-grea...rt-ii#stream/0

[usradcoll1]

Originally Posted by merlinmaxwell

The "ballast tube" in post 5 looks like a simple resistor not a constant (ish) current baretter.

The US type ballast tube was a resistance element that had a certain type of wire that was an iron alloy and not nichrome. It had a surge limiting effect so the tubes had a soft start. Some had a regular enclosure like a metal tube. The ones that had this cover lasted longer because the resistive element didn't rust. Sounds funny but it's true. Moisture also affected resistant line cords.
I had a brand new, never used one that was open. Cheap US tat.
Dave, USradcoll! That my story and stick with it!