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 Post subject: EV Model 870 Matching Transformer
PostPosted: Jan Wed 16, 2019 6:49 am 
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Joined: Apr Sat 18, 2015 3:01 am
Posts: 122
Location: Lexington KY
Does anyone have a spec sheet for an Electro-Voice Model 870 Matching Transformer?

What were these used for?


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 Post subject: Re: EV Model 870 Matching Transformer
PostPosted: Jan Wed 16, 2019 9:08 pm 
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Joined: Nov Sat 07, 2009 11:37 pm
Posts: 2184
Location: Sayreville, NJ 08872
MODEL 870- 12-Watt Line Matching Transformer for mounting on side of
CDP Model 847. Primary taps for 12, 8, 4, 2 and 1 watts with 70 volt line.
Impedance taps for 45, 500, 2500 and 5000 ohms. Size: 2½ in. x 2½ in. x 3 in.;
Shipping Weight: 2 lbs. List Price, Model 870 . . .. . ........... .. . . . . $12.00

Info taken from page 29 of this document:
https://www.google.com/url?sa=t&rct=j&q ... YTr0vVO1-E

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 Post subject: Re: EV Model 870 Matching Transformer
PostPosted: Jan Sun 20, 2019 4:45 am 
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Location: Lexington KY
5000 ohm input. Dang I wonder if you can use that as a amp output transformer. 5K to 8 ohm out.


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 Post subject: Re: EV Model 870 Matching Transformer
PostPosted: Jan Sun 20, 2019 5:04 am 
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Location: Sayreville, NJ 08872
archeus68 wrote:
5000 ohm input. Dang I wonder if you can use that as a amp output transformer. 5K to 8 ohm out.

As long as you don't exceed the ratings, it should work fine. Transformers go both ways.

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 Post subject: Re: EV Model 870 Matching Transformer
PostPosted: Jan Sun 20, 2019 5:25 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4270
Location: Boston, MA USA
Unfortunately no, you cannot use a line matching transformer as a plate output transformer, for several reasons:

1) The primary winding insulation will not withstand the several hundred volts of a plate circuit.

2) If the output is push-pull, the primary would have to be center-tapped which it probably is not.

3) If the output is single-ended, the transformer core must have an air gap to prevent DC saturation, which a matching transformer does not have.

-David


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