OPT for 250th Se A2

tyor · 28th August 2007, 11:29 AM

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?

tyor · 28th August 2007, 07:21 PM

anybody that have a clue on what trafo to use for a 250th in single ended?

Fuling · 28th August 2007, 07:35 PM

Are you asking for a specific brand/model to use or what parameters an OPT should have to match the 250th tube?

tyor · 28th August 2007, 07:51 PM

The parameter.

But if you know a spesific model that I can use so spit out

Fuling · 28th August 2007, 08:44 PM

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.

tyor · 28th August 2007, 09:19 PM

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

tyor · 28th August 2007, 09:25 PM

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

Fuling · 29th August 2007, 11:50 AM

Then Hammonds biggest SE OPT should work. It´s 5k 300mA 75W IIRC

gianis · 30th August 2007, 05:55 PM

250TH amplifier at 1KV H.T. and 4.5kv primary output transf. about 70 W RMS

Gluca · 31st August 2007, 08:05 AM

Great Job! Congrats. Any other pic or info?

Gianluca

28th August 2007, 11:29 AM	#1
tyor diyAudio Member Join Date: Jul 2004 Location: Norway	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?

31st August 2007, 08:05 AM	#10
Gluca diyAudio Member Join Date: Nov 2004 Location: Back to Italy	UH!? OH!? Great Job! Congrats. Any other pic or info? Gianluca

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28th August 2007, 07:21 PM	#2
tyor diyAudio Member Join Date: Jul 2004 Location: Norway	anybody that have a clue on what trafo to use for a 250th in single ended?

28th August 2007, 07:35 PM	#3
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Are you asking for a specific brand/model to use or what parameters an OPT should have to match the 250th tube?

28th August 2007, 07:51 PM	#4
tyor diyAudio Member Join Date: Jul 2004 Location: Norway	The parameter. But if you know a spesific model that I can use so spit out

28th August 2007, 08:44 PM	#5
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	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.

28th August 2007, 09:19 PM	#6
tyor diyAudio Member Join Date: Jul 2004 Location: Norway	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

28th August 2007, 09:25 PM	#7
tyor diyAudio Member Join Date: Jul 2004 Location: Norway	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

29th August 2007, 11:50 AM	#8
Fuling diyAudio Member Join Date: Aug 2001 Location: Sweden (Mora)	Then Hammonds biggest SE OPT should work. It´s 5k 300mA 75W IIRC