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Old 28th August 2007, 11:29 AM   #1
tyor is offline tyor  Norway
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Default OPT for 250th Se A2

Hi i am planning to build a SE A2 amp with 250th tubes. I dont know what output transformator I should use. I have been looking at LL1691 from Lundahl http://www.lundahl.se/pdfs/datash/1691.pdf Wil that be a good one?
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Old 28th August 2007, 07:21 PM   #2
tyor is offline tyor  Norway
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anybody that have a clue on what trafo to use for a 250th in single ended?
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Old 28th August 2007, 07:35 PM   #3
Fuling is offline Fuling  Sweden
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Are you asking for a specific brand/model to use or what parameters an OPT should have to match the 250th tube?
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Old 28th August 2007, 07:51 PM   #4
tyor is offline tyor  Norway
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The parameter.

But if you know a spesific model that I can use so spit out
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Old 28th August 2007, 08:44 PM   #5
Fuling is offline Fuling  Sweden
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The only plate curves I can find for 250th are drawn in "constant current mode" which gives me no hints of a suitable point of operation. A quick google search revealed nothing, but when I say "quick" I mean it. Some info must be available somewhere.
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Old 28th August 2007, 09:19 PM   #6
tyor is offline tyor  Norway
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When I asked on a forum 2.5 years ago, I got this answer

1 kvdc 200 mA Gv of +40 would call for an OPT primary of about 4k5, and [if properly implemented] would probably be good for about 60-70 Watts. Assuming we can trust the tube curves, grid current would remain under 25 mA.

and 3-250A4 is the same tube
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Old 28th August 2007, 09:25 PM   #7
tyor is offline tyor  Norway
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here are some data for the tube or substitutes

http://www.mif.pg.gda.pl/homepages/f.../t/TB4-800.pdf
http://tdsl.duncanamps.com/pdf/vm076.pdf
http://www.nj7p.org/Tube4.php?tube=3-250A4
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Old 29th August 2007, 11:50 AM   #8
Fuling is offline Fuling  Sweden
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Then Hammonds biggest SE OPT should work. Its 5k 300mA 75W IIRC
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Old 30th August 2007, 05:55 PM   #9
gianis is offline gianis  Greece
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Default tube

250TH amplifier at 1KV H.T. and 4.5kv primary output transf. about 70 W RMS
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File Type: jpg th250.jpg (41.1 KB, 619 views)
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Old 31st August 2007, 08:05 AM   #10
Gluca is offline Gluca  Italy
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Default UH!? OH!?

Great Job! Congrats. Any other pic or info?

Gianluca
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