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Old 22nd April 2010, 07:58 AM   #1
hrnous is offline hrnous  Czech Republic
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Default Output transformers

Hi, i have two output transformers, one with power 70w and Raa 4k and one with 130w and Raa 2k3 is any suitable for GU50 tubes ? both are designed for 550V Ua and EL34
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Old 22nd April 2010, 02:10 PM   #2
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4k is suitable for SE GU50.
2k3 is suitable for 2 parallel GU50 SE.
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Old 22nd April 2010, 02:17 PM   #3
hrnous is offline hrnous  Czech Republic
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this transformers are ONLY for PP, not SE, btw SE with GU50 and 130W output is not very real
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Old 22nd April 2010, 02:45 PM   #4
bigwill is offline bigwill  United Kingdom
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Just to be helpful, an output transformer with an anode to anode impedance of say 4000 ohms will present a load of 2000 ohms to each valve while in class A.

Why? Well, a 4000 ohm winding is actually two 1000 ohm windings in series (with a centre tap in the middle), because impedance is the square of turns ratio. If you double the turns on a winding, the apparent impedance of that winding quadruples (provided the "other" winding stays constant)

Why does each valve see 2000 ohms then? Each valve is working into its own 1000 ohm load (remember that B+ sits on the centre tap and stays constant), but since they are coupled, the load is shared roughly equally between them. As one moves into Class-AB, one valve cuts off and the other then sees the entire 1000 ohm load.
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Old 22nd April 2010, 03:39 PM   #5
Arnulf is offline Arnulf  Europe
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If those OPTs are meant to be used with 4R speakers you might get away with the nominal 4K transformer in PP and 6R speakers.
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Old 22nd April 2010, 04:02 PM   #6
hrnous is offline hrnous  Czech Republic
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ok, i know calculations about reflect impedance and etc, i have 8 and 15R output, but i need to find "ideal" impedance for gu50 with HT 550v or internal resistance of gu50
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Old 22nd April 2010, 04:08 PM   #7
hrnous is offline hrnous  Czech Republic
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i found this info about gu50 datasheet, Röhren-Verstärker mit der LS 50 (GU 50)

datasheet says 600v 2k5 and -48V on g1, but in schematcs is 600v ht and 2k5 transformer..
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Old 22nd April 2010, 08:05 PM   #8
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Datasheet says 5k a-a and schematic shows 2k5 a-a for parallell tubes, that is consistent.

/Olof
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Old 22nd April 2010, 08:08 PM   #9
hrnous is offline hrnous  Czech Republic
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i´m dude
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