Philco First Audio Replacement - Printable Version
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Philco First Audio Replacement - Radio Hound - 04-17-2018
Hi, I am working on a Philco model 90 Cathedral radio. This has been a real work in process. I have successfully replaced the main transformer, speaker and all bad wiring. By the way, I started a thread on trying to sort out the transformer windings and I got called away to work for several days so I did not get back. I am sorry I did not close that thread. I did not mean to disrespect those that gave direction. I respect you guys a lot. I figured the transformer out and it tests perfect. The last problem I have is the first audio transformer is burned out too. I have been everywhere to try to find a used part and I am giving up. My question is, is there a new transformer out there that would work as a replacement for the first audio. This is a push pull twin 45 tube model.
RE: Philco First Audio Replacement - Radioroslyn - 04-17-2018
https://www.tubesandmore.com/products/transformer-audio-interstage-10-ma
RE: Philco First Audio Replacement - Radio Hound - 04-17-2018
Thank you so much Terry. I ordered it. Just for educational purposes, is it possible to teach me how to calculate that in the future. It had open windings on it because it had overheated and I couldn't ohm it out. How would I do that math to see what to order. I want to understand so bad. I feel all alone here in Indiana lol.
Thx,
Hound
RE: Philco First Audio Replacement - Radioroslyn - 04-17-2018
> 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
RE: Philco First Audio Replacement - Radio Hound - 04-17-2018
Thank you so much for the explanation and I need the luck lol.