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 Post subject: audio transformers
PostPosted: Nov Sat 09, 2019 8:08 pm 
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Joined: Nov Sat 09, 2019 2:56 am
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HI everyone ,i have open audio transformers on 2 radios ,a freshman masterpiece and a radiola 20.which is the best or least expensive way to go,rewind them myself or have someone do it if i do it what are the ratios for primary and secondary,also are there other new type circuit boards you could replace them with. i know about those hammond type transformers but what else is out there.thanks.


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 Post subject: Re: audio transformers
PostPosted: Nov Sun 10, 2019 4:08 am 
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Joined: Nov Tue 14, 2017 5:09 am
Posts: 2017
Location: Austin, Texas
Those transformers are usually in the 1:3 to 1:5 range. They step up the voltage from the plate of one stage to the grid of the next.

If you don't care about audio quality, you can use a low power 24 or 48 volt power transformer operating in reverse of it's normal primary and secondary.
A 24VAC transformer is a 1:5 ratio and a 48VAC is 2.5:1. The plate of one stage drives the low voltage side of the transformer and the original 120VAC primary drives the grid of the next stage.

Actually, some of the 1920's audio transformers were so bad that a modern 60 Hz AC transformer might improve the audio.

Other than rewinding the transformers yourself, the next cheapest fix is probably to buy replacement windings from Antique Radio Supply but you have to have original transformers with the correct core size.

Jay


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 Post subject: Re: audio transformers
PostPosted: Nov Sun 10, 2019 2:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 9345
Location: Beaver Falls, PA. USA
You might get lucky and find an older replacement transformer at a swap meet, or on the bay; make sure that the windings have continuity.

There are a couple of circuits out there which use transistors to replicate the function of the transformer.

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 Post subject: Re: audio transformers
PostPosted: Nov Sun 10, 2019 5:47 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 37563
Location: Livermore, CA
AES, www.tubesandmore.com sells audio interstage transformers.

https://www.tubesandmore.com/products/t ... ers_chokes

P-T156 is a complete transformer 1:3 ratio. P-T431 is just the coil, no metal core. The coil will fit original audio interstage transformer in Radiola 20. Not sure what transformers are in your Freshman Masterpiece.

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 Post subject: Re: audio transformers
PostPosted: Nov Sun 10, 2019 5:51 pm 
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Joined: May Sat 30, 2015 11:49 pm
Posts: 903
Location: Keystone Heights, FL, USA 32656
Least expensive is to use a capacitor from P to G and resistors to by-pass the open windings. Less final volume but usually OK to drive headphones or speaker.
Then trouble shoot the rest of the radio, get it working and then decide if you want to replace/rewind the transformers. This method also leaves the original transformers in place, it that is important to you.

Read this: http://www.antiqueradios.com/chrs/journ ... rmers.html

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Jeff
“Nothin’s worth nothin ‘till somebody wants it.”—Irv Metter


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