Posts: 24
Threads: 6
Joined: Jan 2020
City: Laceys Spring
State, Province, Country: Alabama
Wondering if anyone can give me some information about an output transformer on an AA5 that uses a 50C5 power output tube. The radio im working on is a Silvertone catalog number 6 radio. I've completed the recap and changed several of the out of tolerance resistors. When I checked the output transformer windings, the primary measures 336 ohms and the secondary measures .6 ohms. According to the schematic, the primary should be 185 ohms and the secondary .6 ohms. Was wondering, can output transformers go up in value like resistors do when they get old or could this be a change in the transformer specs when the radio was made. Sometimes manufacturers change specs and they don't make it into an updated schematic; I could be wrong here. Anyway, can I use this transformer or should Iook for a replacement? Don't want to burn up a tube or something. Thanks for any suggestions.
Posts: 7,323
Threads: 270
Joined: Dec 2009
City: Roslyn Pa
I wouldn't loose any sleep over it.
The dc resistance doesn't mean a whole lot as a number to verify the the ac impedance of the primary. As for burning up something the worst that could (but unlikely) is that the primary could open up do to excessive current flow. This would have to do with the rating of the transformer and not the set itself. If there was a mismatch between the tube and transformer you would have low volume and distortion. The ratings for many of the tubes used in ac/dc sets are the same so a transformer that was used with a 50C5 could be used with a 50B5, 50L6, 35L6, 35C5, 35B5, 25B6, and 25L6 there probably a few more. Transformers from an ac set using tubes like 2A5, 47, 42, 41, 6F6, 6V6, and 6F6 aren't a good match as these tube have a higher plate load impedance.
OBTW to answer your question no. Just like wire wound resistors they don't drift like carbon counterparts.
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 it!
Terry
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Wirewound resistors and anything wirewound do not just go up in value.
If your transformer measures twice the value written this possibly could mean two things: 1) error in the sch. 2) the xfmr was replaced at some point.
If it works it is a good transformer. Is it original - can't tell you. Maybe not.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
