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 Post subject: Transformer Question
PostPosted: Nov Fri 09, 2018 2:33 am 
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Joined: Feb Fri 22, 2008 3:28 am
Posts: 405
I have been working on an older Trio 9R-4J receiver. When I got it it had a transformer connected under the chassis for the audio output. I removed it since it had been very poorly installed and was in the way. It didn't appear to be an original item. I did some tests on it and the impedance didn't seem correct for the tube that was installed (that was fried BTW). Using a variac I got 1VAC out with 75VAC in. This would seem to make the impedance like 15K with a 4 ohm speaker if I calculated correctly. The output tube was a 6AQ5 set up single ended which requires a 5K to voice coil so this seems way too high.

DC resistance on the primary was 360 ohms, secondary maybe .2 ohm. There is a small schematic on the top showing a jack labeled tip/ring/sleeve with the other side voice coil and a speaker symbol. There was also a number on the schematic SC-A-3725-A. May be military since it has metal end caps.

Any idea what this transformers intended use may have been? What output tube (if any) it was intended to be used with?


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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 2:35 am 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 352
Location: Stone Mountain, GA
Tip + ring would be telephone use.

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Scott.
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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 2:43 am 
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Joined: May Tue 30, 2006 4:46 pm
Posts: 9486
Location: Santa Rosa, CA
Quote:
Tip + ring would be telephone use


Or also for headphone jack wiring.

Rich


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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 2:51 am 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 263
Location: 18424 PA
Try using a signal generator at 1khz. Using the variac you are trying to push 60hz through and it might not have the core size to do that. Put 1v on the sec, measure the primary, much easier. 6aq5 isn't gonna really care what impedance, 4k, 5k, 8k,.


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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 3:07 am 
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Joined: Feb Fri 22, 2008 3:28 am
Posts: 405
I will try the audio generator as suggested.

I was looking on line and stumbled across a site that showed the inside of a military LS-3 speaker; the transformer inside had an almost exact small schematic as the one on the transformer I have, complete with tip/ring sleeve, etc. Likely this transformer was used in some military speaker enclosure.


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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 4:09 am 
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Joined: Sep Mon 03, 2018 2:24 am
Posts: 652
I would purchased a used correct audio transformer off of ebay. Some list primary & secondary impedance or tube that was used with the transformer.


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 Post subject: Re: Transformer Question
PostPosted: Nov Fri 09, 2018 4:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5029
Location: Rochester NY USA
60 Hz is fine for measuring a transformer - frequency won't effect the unloaded ratio, though obviously the primary impedance drops with frequency and it will load the source more. 5-8K primary is typical for 6AQ5 (or 6AR5, commonly used in Japanese equipment)


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 Post subject: Re: Transformer Question
PostPosted: Nov Sat 10, 2018 7:21 am 
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Joined: Sep Mon 16, 2013 2:42 am
Posts: 2919
Location: Tucson, Arizona U.S.A.
Quote:
frequency won't effect the unloaded ratio

But it can affect the measurement if the core is too small and saturates. Then the output voltage would be lower than what the turns ratio would suggest.

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Jim Mueller


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