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 Post subject: R-390 audio transformer replacement
PostPosted: Sep Wed 13, 2017 4:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17500
Location: Warner Robins, GA
I have an R-390 and am looking at replacing the audio transformer which drives the audio filters.

In another topic it was mentioned the UTC A-24 would be a good replacement, but found I needed a UTC A-25 as that one is meant to have DC on the primary. The A-25 has a response of 40-20KHz.

I do not want to try and find one and pay the high price these go for.

What would be a good sub for that transformer and what would be a good sub with a 10K primary that has the same frequency response?


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 Post subject: Re: R-390 audio transformer replacement
PostPosted: Sep Wed 13, 2017 11:27 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 6967
Location: Long Island
If you are talking about the R-390 communications receiver and you care about maintaining the original performance, the best thing would be to find a transformer from a parts set. Passive filters, whether they be LC, mechanical, crystal or ceramic, or any combinations thereof, are designed for specific input and output impedances. Replace the driver transformer with anything the factory didn't use or recommend and you'll probably get audio out of the radio but you are on your own as far as the filtering.

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 Post subject: Re: R-390 audio transformer replacement
PostPosted: Sep Wed 13, 2017 11:43 pm 
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Joined: Jul Fri 18, 2008 10:02 am
Posts: 1972
Location: near ST Louis Mo 62002
An utc O-8 or O-9 would work .

http://www.bunkerofdoom.com/xfm/UTC_1955_WEB/019.jpg

I have a couple of O-9s , if you have something to trade

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 Post subject: Re: R-390 audio transformer replacement
PostPosted: Sep Thu 14, 2017 12:14 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17500
Location: Warner Robins, GA
The transformer itself is good I just want something with a better low frequency response.

The 0-9 won't work unfortunately as it has about the same frequency response as the good originals.


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 Post subject: Re: R-390 audio transformer replacement
PostPosted: Sep Thu 14, 2017 1:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10755
Location: Mpls, Minnesota
Why would you be worried about frequency response on a communications receiver, it was designed for optimal voice frequencies.

Dave


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 Post subject: Re: R-390 audio transformer replacement
PostPosted: Sep Thu 14, 2017 4:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17500
Location: Warner Robins, GA
Because I don't use it just for voice.

I often listen to it when I have my two tube transmitter fed the online feed of WRDV.


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