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Old 29th December 2012, 06:45 PM   #61
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i use some lundahl 1620 /120ma which can be set for 11k5 which is what i use, think at that impeadence they are only rated at 14w, i was testing yesterday and saw 16v into 8.8r so 29 w at some massive clipping.
still they were 200 delivered about 15 years ago

enzo
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Old 29th December 2012, 06:47 PM   #62
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I thought they were more like 2k6?
enzo
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Old 31st December 2012, 09:24 PM   #63
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Quote:
Originally Posted by cotdt View Post
Of course distortion will get lower with higher impedance transformers, but that is not the goal for a SET amp. The GM70 has output impedance at 1.1k, so a 4.4k transformer makes more sense. I use a 5k but it sounds great even with 3.5k transformer.
True, but not the point I was trying to make. The GM-70 (in particular) is more sensitive to loading (in terms of IMD) than many tubes of its ilk (845, 572, 211, etc.) so I don't agree that "4.4K makes more sense" - (you can talk with Jack Elliano of Electra-Print if you need actual test results).
Also, I would say that lowering IMD is the goal of any amp as it's by far the most objectionable form of distortion.

That being said, much of this depends on operating bias (quiescent voltage/current) and you do get wider frequency response (less inductive roll-off) with a 5K winding than w/10K.

All designs are compromises of one sort or another.
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