Output Transformer Testing

The
results of Transformer testing underline herewith are performed under following
scenario:
Associated
Test Equipments: 
Fig.1 
The Frequency Response Testing according to Fig.1 represents the ability of each transformer to perform under real working condition with 70mA unbalanced DC at relatively high power level (18Vpp output or 5 Watts RMS to 8 ohms load). 
Fig.2 
The Pulse Behavior (square wave) Testing according to Fig.2 represents the ability of each transformer to response to perfect square waveform. Since square waveform composes of fundamental frequency plus indefinite number of harmonic 2nd, 3rd, 4th, 5th and so on. This test puts transformer to its extreme condition. Output Transformer must handle high number of harmonics at one pulse cycle and will show out its unique characteristic. Good transformers could be observed by smooth waveform with minimal raise/fall time. Good transformers also exhibit less ringing behavior even at high power level. 
Model
Picture

Brand

Silk
Transformer

Model

S325


Description

3K/20Watts
output transformer with EI (M6) Lamination. Although S325 can not go
as high as Tango XE20S but comparable to U808. It has smooth waveform
response. (No peak, No dip) With its high inductance, S325 also performs
very well in bass region. (see 40Hz waveform that tilt less than U808)


Primary
Impedance (ohm)

3.0K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

197


Primary
Inductance (H)

19.6H/16.5H


Leakage
Inductance (mH)

2.8mH/7.5mH


Quality
Factor (Pi/Li)

7000/2200


Primary
Capacitance (nF)

1.15nF/102.9nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHz

20
KHz

Model
Picture

Brand

Tango

Model

XE20S


Description

Universal
output transformer with oriented hiB cut core. With hiB core, the transformer
has lower primary turn (Less copper loss) than U808 but also lower primary
inductance. Excellent High Frequency response that could go above 100KHz
but be observed the small ringing waveform.


Primary
Impedance (ohm)

3.5K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

114


Primary
Inductance (H)

12.2H/10.7H


Leakage
Inductance (mH)

6.3mH/13.4mH


Quality
Factor (Pi/Li)

1936/798


Primary
Capacitance (nF)

1.9nF/154nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHZ

20KHZ

Model
Picture

Brand

Tango

Model

U808


Description

Universal
output transformer with EI core. The transformer processes very linear
frequency response with smooth waveform. Due to its small core size, it
has limited primary inductance compare to other big irons.


Primary
Impedance (ohm)

3.5K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

210


Primary
Inductance (H)

17.1H/14.8H


Leakage
Inductance (mH)

5.7mH/117.8mH


Quality
Factor (Pi/Li)

3000/125


Primary
Capacitance (nF)

1.4nF/116nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHz

20
KHz

Model
Picture

Brand

Audio
Note

Model

Trans152


Description

2.5K
nonpotted output transformer with M6 EI core. Although it has small primary
turn (around 1,800T1,900T) due to its large core size, TRANS152 has
moderate primary inductance. A dip in frequency response presents at 40KHz.
Waveform is on par.


Primary
Impedance (ohm)

2.5K


Secondary
Impedance (ohm)

4,
8


Primary
DCR (ohm)

157


Primary
Inductance (H)

13.5H/14.13H


Leakage
Inductance (mH)

11.33mH/15.41mH


Quality
Factor (Pi/Li)

1,015/916


Primary
Capacitance (nF)

1.88nF/133nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHZ

20KHZ

Model
Picture

Brand

Golden
Tube

Model

SE40


Description

1.9K
SE parallel output transformer extracted from Golden Tube Audio model
SE40. Perform well considering it was mass product in mid range price.


Primary
Impedance (ohm)

1.9K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

120


Primary
Inductance (H)

8H/10H


Leakage
Inductance (mH)

NA


Quality
Factor (Pi/Li)

NA


Primary
Capacitance (nF)

NA


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHz

20
KHz

Model
Picture

Brand

James

Model

JS6123HS


Description

Universal
output transformer with EI core that performs far behind Tango U808.
Observe the big 12.0dB dip at around 80KHz and bounce up to resonant
up to 2.0MHz!


Primary
Impedance (ohm)

3.5K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

181


Primary
Inductance (H)

12.6H/13.9H


Leakage
Inductance (mH)

167mH/NA


Quality
Factor (Pi/Li)

75.4/NA


Primary
Capacitance (nF)

2.0nF/124nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHz

20
KHz

Model
Picture

Brand

Hammond

Model

1628SE


Description

5K
output transformer with EI (M6) lamination. It has highest inductance
in the group but also has excessive primary DCR of over 400 ohms! (A lot
of copper loss) Hammond has 10 to 15KHz frequency dip of 4.0dB! The waveform
is anomaly beyond 5.0KHz.


Primary
Impedance (ohm)

5K


Secondary
Impedance (ohm)

8


Primary
DCR (ohm)

439


Primary
Inductance (H)

64.5H/40.78H


Leakage
Inductance (mH)

28.7mH/40.5mH


Quality
Factor (Pi/Li)

2247/1006


Primary
Capacitance (nF)

374pF/43.05nF


Frequency
Response


Square
Wave Picture


40
Hz

1
KHz


10
KHz

20
KHz
