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Old 31st Aug 2019, 1:14 pm   #44
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
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Default Re: Interstage Audio coupling transformer

Originally Posted by ChristianFletcher View Post
Now I’m still going to rewind the transformer, but cannot help thinking why did they bother to use a transformer when capacitor coupling works well and would have been cheaper.

Of course in these radios gain came at a premium price, every amount was a precious commodity in radios of the 1920's and 30's. So it was a good idea to add passive gain with the transformer, rather than another valve stage. You are probably in an area of strong transmitter fields and all seems well without the transformer. But on that threshold where the radio was in a peripheral area far from the transmitter, the transformer gives some advantage.

This more applies to isolating transformers: Due to to the transformers band-pass response they are helpful in filtering off the RF component from the grid leak detector stage's anode that drive the primary in many 1920/30's TRF radio designs, so these RF signals do not end up at the grid of the output valve, this saves on some capacitors. And they have the other advantages Kalee20 pointed out too.

Last edited by Argus25; 31st Aug 2019 at 1:20 pm.
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