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RE: Found a great driver tube in the 6BL7

Posted by dave slagle (M) on November 28, 2015 at 09:39:04

In Reply to: RE: Found a great driver tube in the 6BL7 posted by Triode_Kingdom on November 27, 2015 at 15:23:27:

I keep hearing people say that the BX and BL7's aren't nearly as linear as the SN7 and I wonder where that comes from.

I just ran some spice sims running the tubes with a CCS load and the following currents with a 10V bias with all three swinging 120V P-P

SN7=10ma
BL7=15ma
BX7=20ma

The overall distortion of the SN and BL were nearly the same with the BX having a touch more 2nd.

The actual distortion numbers are below.

Fourier components of V(out_bl7)

Harmonic Frequency Distortion
[#] [Hz] .......... [%]
1 1000 .......... 100
2 2000 .......... 0.796
3 3000 .......... 0.599
4 4000 .......... 0.023
5 5000 .......... 0.370
6 6000 .......... 0.019
7 7000 .......... 0.197
8 8000 .......... 0.002
9 9000 .......... 0.085
Total Harmonic Distortion: 1.084143%


Fourier components of V(out_sn7)

Harmonic Frequency Distortion
Number [Hz] .......... [%]
1 1000 .......... 100
2 2000 .......... 0.848
3 3000 .......... 0.537
4 4000 .......... 0.021
5 5000 .......... 0.365
6 6000 .......... 0.020
7 7000 .......... 0.195
8 8000 .......... 0.002
9 9000 .......... 0.085
Total Harmonic Distortion: 1.088743%


Fourier components of V(out_bx7)

Harmonic Frequency Distortion
Number [Hz] .......... [%]
1 1000 .......... 100
2 2000 .......... 0.962
3 3000 .......... 0.546
4 4000 .......... 0.007
5 5000 .......... 0.360
6 6000 .......... 0.019
7 7000 .......... 0.194
8 8000 .......... 0.002
9 9000 .......... 0.085
Total Harmonic Distortion: 1.182439%

I increased the current as the tubes went down in gain / Rp to get away from the Knee increasing current didn't change things much but decreasing the current on the BX BL 7's below 10ma did start to separate them from the "low distortion pack".

dave

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