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Old 8th August 2013, 11:01 PM   #1
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Default Lundahl Output transformers?

Why are there various output power ratings depending on the connection combination of the primary load?

Say, you have a transformer with:

10K / 40W

6K / 100W

3K / 160W

These are just sample numbers, but I am just curious about their ratings. How are these outputs? Comparable to Sowter, etc.?

Thanks!

Blair
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Old 8th August 2013, 11:19 PM   #2
jcx is offline jcx  United States
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VT limit? - if the power is speced for a certain low pass corner frequency, distortion % ~ Bmax operating point target
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Old 9th August 2013, 06:47 AM   #3
kmtang is offline kmtang  Canada
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My friends and I used number of Lundahl's output transformer. They are really good indeed with reasonable price. We all end up with Amorphous core OPT's for both singled ended and push pull amplifiers.
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Old 9th August 2013, 09:12 AM   #4
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The transformer hits its Bmax with some voltage of some frequency, say 100 Vrms at 30 HZ. Depending on the reflected load at the primary, this means 4 W/2,5 KOhm (100*100/2500), or 2 W/5KOhm, or 8 W/1,25KOhm.

The reflected load depends on the configuration of the secondary, which in Lundahl's case consists of multiple windings. You can arrange the secondary windings so that it reflects e.g. either 2,5 KOhm with a 8 Ohm load, or 5KOhm.
The same holds true for the case of intended mismatch at the secondary: If you load the 8 Ohm winding of a 5K/8 Ohm transformer with 4 Ohm, you get 2,5KOhm reflected impedance at the primary.
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Old 9th August 2013, 07:53 PM   #5
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Gotcha! Thanks!

I just bought a pair of LL1679s on eBay. Like I need another pair of transformers

http://www.lundahl.se/pdf/1679.pdf

So, this should be good for a quad of KT88s into this transformer wired for 2.6K?

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Blair
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Old 9th August 2013, 08:16 PM   #6
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What I would like to know, is how Lundahl can make a 700W OPT at 4.5kg, compared to a Hammond 280W at 10+ kg. Both claim to go down to 30Hz. Did someone compare these two perhaps? I'm very interested in the Lundahl, since it weighs as much as the Hammind 1650T (120W), but with much more flexibility.
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Old 9th August 2013, 08:23 PM   #7
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That's actually what got me curious as well. I have a pair of 1650Ts and a pair of 200W Sowters as well. Unfortunately, they all have different primary impedance. I can't roll them in and out of a circuit.

Click the image to open in full size.

That Sowter is a beast!
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Old 9th August 2013, 08:32 PM   #8
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Quote:
Originally Posted by funk1980 View Post
What I would like to know, is how Lundahl can make a 700W OPT at 4.5kg, compared to a Hammond 280W at 10+ kg. Both claim to go down to 30Hz.
Different core geometry and materials, different winding techniques...
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Old 9th August 2013, 08:41 PM   #9
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Quote:
Originally Posted by funk1980 View Post
What I would like to know, is how Lundahl can make a 700W OPT at 4.5kg, compared to a Hammond 280W at 10+ kg. Both claim to go down to 30Hz. Did someone compare these two perhaps? I'm very interested in the Lundahl, since it weighs as much as the Hammind 1650T (120W), but with much more flexibility.
You need to compare core cross-section, not overall size.

BTW, I don't think its possible to build 700W audio transformer weighting 4.5 kg with lowest frequency at full power 30 Hz. I assume this is typing error. Either this is 70W transformer either it weights 14.5 kg.

PS. I opened one of the Lundahl data sheets. Looks like you mixed "V" and "W" - 700V (max primary RMS voltage) with output power (in Watts).

Last edited by LinuksGuru; 9th August 2013 at 08:48 PM.
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Old 9th August 2013, 09:29 PM   #10
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They are C core, but I don't know the material. The cores may be significantly lighter.
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