04-17-2018, 05:24 PM
> It had open windings on it because it had overheated and I couldn't ohm it out.
I doubt it. Typically it fails from the small dia wire used on the secondary winding corroding.
> How would I do that math to see what to order.
I keep it simple. Primary has to be able to handle plate current from the previous tube. A quick check in the RCA tube manual sez that it's abt 5ma@250v. Transformer is good for 10ma. Plate load resistance is abt 9K which is a good match for this transformer. The grid resistance isn't particularly critical it just has to high, something around 100K is good. This transformer is a good general replacement for a lot of applications, like in early battery and AC sets.
Sometimes it boils down to availability and cost. Some sets use odd transformer setups that are unreplaceable by using common replacements that are current or from years gone by. The Philco 37 and 38-690 come to mind. These can be rewound but it comes at a price. In some instants there is a work around to use a common transformer.
> I want to understand so bad.
Right up my alley I can explain it really badly!!!
GL
I doubt it. Typically it fails from the small dia wire used on the secondary winding corroding.
> How would I do that math to see what to order.
I keep it simple. Primary has to be able to handle plate current from the previous tube. A quick check in the RCA tube manual sez that it's abt 5ma@250v. Transformer is good for 10ma. Plate load resistance is abt 9K which is a good match for this transformer. The grid resistance isn't particularly critical it just has to high, something around 100K is good. This transformer is a good general replacement for a lot of applications, like in early battery and AC sets.
Sometimes it boils down to availability and cost. Some sets use odd transformer setups that are unreplaceable by using common replacements that are current or from years gone by. The Philco 37 and 38-690 come to mind. These can be rewound but it comes at a price. In some instants there is a work around to use a common transformer.
> I want to understand so bad.
Right up my alley I can explain it really badly!!!
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
