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Old 21st July 2010, 06:33 AM   #1
Will is offline Will  Malaysia
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Location: Kuala Lumpur
Default LL1682PP Lundahl

I couldn't search this transformer topic in the archives and Per Lundahl is on summer vacation so I thought I'd post the topic here if anyone has used this trans.

http://www.lundahl.se/pdfs/datash/1682.pdf

The beauty of this transformer is that it can be used for SE and PP applications hence flexible.

I used this on an Audion Sterling on Triode Mode 6550C connecting to the 5.5K primary and 10ohm secondary winding. VDC supply at 470V and cathode resistor of the 6550C is 500 ohms.

Since this trans has 2 halfs of the primary, can it be used for UL feedback 50% to the grid of 6550C ?

Another question is that the trans rating is at 8W in SE mode (acc to the datasheet). Can it take the increase in power when connected in UL mode?
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Old 21st July 2010, 09:48 AM   #2
OneyedK is offline OneyedK  Belgium
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Will, I think you misread the specs.
LL1682 is available in SE an PP versions, both versions have different cores (gap).
Basic versions are
LL1682/PP
LL1682/50mA (SE)
LL1682/100mA (SE)
There are some limited runs of SE versions with different max. primary current.

If you have one of the LL1682 SE versions, the 50% is ok for UL connection.
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Old 21st July 2010, 11:32 AM   #3
Will is offline Will  Malaysia
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Quote:
Originally Posted by OneyedK View Post
Will, I think you misread the specs.
LL1682 is available in SE an PP versions, both versions have different cores (gap).
Basic versions are
LL1682/PP
LL1682/50mA (SE)
LL1682/100mA (SE)
There are some limited runs of SE versions with different max. primary current.

If you have one of the LL1682 SE versions, the 50% is ok for UL connection.
Hi,
I don't think I misread it; the transformer is really that flexible.
I have 2 pairs of this and I've used it in SE and PP configs before.

You can see here that its price is only quoted for either 1682 standard or 1682AM (means amorphous core). Both windings are presumably the same:
K & K Audio - Lundahl Transformers, audio DIY kits and more

I'm just not sure if the increase in power when connected in UL mode will destroy the trans.
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Old 21st July 2010, 12:14 PM   #4
ddd is offline ddd  Bulgaria
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OneyedK is right. Just look at this:
http://www.lundahl.se/pdfs/datash/1682.pdf
If you have the SE version, UL will increase the output power, but the Rout as well. So, you should choose the mode by listening test.
No danger for the trafo itself.
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Old 21st July 2010, 12:26 PM   #5
kmtang is offline kmtang  Canada
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Hi Will,

The label on the transformer should be marked whether it is for PP or SE with specified idle current.

Surely, I believe the SE OPT can be used for PP but it won't have the performance of the one designed for PP of the inductance, and the larger air-gap which would cause the crossover distortion (my guess).

You may get to KandKaudio.com's forum and ask Kevin about this. Usually, Kevin answers very quickly.

Johnny
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Old 21st July 2010, 12:44 PM   #6
Will is offline Will  Malaysia
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Right, thanks for the suggestions guys.
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