6LU8 SET or SEUL Amp
I did this one about 12 years ago. It compares very well with what you can do with a 2A3, but at a much lower cost. And 6LU8s are still cheap, all built while production knew how to make a reliable tube.
The distortion tests were done with an HP302A Wave Analyzer for both triode & UL modes at One Khz. Another short set at 100 Hz, One Watt compares Hammond 125E Universal with a Hammond 1628SE. The advantage of more iron is quite obvious.
ULTRALINEAR WITH FEEDBACK WATTS 1 2 3 4 5 6
HARMONIC DISTORTION % 2ND 0.28 0.44 0.45 0.53 0.74 1.18
3RD 0.16 - - 0.35 0.36 0.96
DAMPING FACTOR = 17
ULTRALINEAR WITHOUT FEEDBACK WATTS 1 2 3 4 5 6
HARMONIC DISTORTION % 2ND 2.71 3.93 5.09 6.65 7.71 7.62
3RD 0.70 0.80 1.10 1.20 1.43 4.05
DAMPING FACTOR = 2.3
TRIODE WITH FEEDBACK WATTS 1 2 3 4 5
HARMONIC DISTORTION % 2ND 0.71 1.04 1.30 1.66 1.98
3RD 0.22 0.25 0.49 0.50 0.79
TRIODE WITHOUT FEEDBACK 2ND 3.95 5.83 7.11 8.93 8.83
3RD - 0.23 0.21 0.20 2.07
Following measured at 100 Hz
OUTPUT TRANSFORMER 125E 1628SE
A) ULTRALINEAR WITHOUT FEEDBACK
HARMONIC DISTORTION % 2ND 15.3 2.9
3RD 3.1 0.4
B) TRIODE WITHOUT FEEDBACK
HARMONIC DISTORTION % 2ND 12.2 2.8
3RD 1.5 ---
Hope this comes out your end OK. Cheers, John
Last edited by John L Stewart : March 16th 11 at 04:21 PM
Reason: Problems with tables
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