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 Post subject: Audio Speaker Transformer
PostPosted: May Wed 15, 2019 11:28 pm 
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Location: Cincinnati, Ohio
Hi

I have a Jackson Bell model 84 Peter Pan radio that the audio speaker transformer is bad and not fixable. How do you know what to buy to replace it?? Never had to do it before.


http://www.nostalgiaair.org/pagesbymode ... 009673.pdf

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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 12:03 am 
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Location: Austin, Texas
You look at the specification for the output tube. In this case, a type 47.
For typical operation, the load resistance is 7000 ohms and the output power is 2.7 watts.
Then you look for an output transformer that has at least that power rating and will match a 4 ohm speaker to something around 7000 ohms.
You will probably find 5000 ohm and 10000 ohm transformers. Either will work OK with the 47.

Jay


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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 1:50 am 
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Location: Cincinnati, Ohio
Would this work?

https://www.mouser.com/datasheet/2/177/124-1389974.pdf

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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 2:26 am 
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Location: Austin, Texas
No, that's an interstage transformer, not a speaker transformer.
A Hammond 125BSE should work OK.
The smaller 125ASE is rated at 3 watts but only 25mA of primary current. The 47 typically runs about 31mA of plate current so the 5 watt transformer is needed.

Here is one place to buy it: https://www.arrow.com/en/products/125bse/hammond-manufacturing

If you don't want to pay that much, there are sites that sell used transformers and you could also put a wanted ad on the Classified forum.

The Hammond 1750C should also work OK and is a lot cheaper since it doesn't have as many windings.
https://www.arrow.com/en/products/1750c/hammond-manufacturing

Jay


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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 12:43 pm 
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Thanks again...... just to make sure that I hook it up right. The primary and secondary. Is the drawing right?


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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 1:22 pm 
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Location: Austin, Texas
It's the other way around. The primary is driven by the 47 and the secondary drives the speaker.

Jay


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 Post subject: Re: Audio Speaker Transformer
PostPosted: May Thu 16, 2019 1:54 pm 
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I am glad I asked :D

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