Output
Transformer Testing

The results of Transformer testing underline herewith are
performed under following scenario:

Associated
Test Equipments:
Hameg HM-504 50MHz 2CH Oscilloscope

Escort EFG-3210 2MHz Sweep/Function Generator
Tenma
72-960 LCR Meter
Fluke 19 Digital Multi Meter
8
ohms Dummy Load

We take great care to provide the most accurate
numbers/figures according to the tolerance of the test equipments.

1) Primary Inductance (Tested at 1KHz and 120Hz) in Henry
indicates transformer capability of producing low distortion at
low frequency. Higher figure means the better bass response with
less distortion.
2) Leakage Inductance causes roll off at high
frequency. The lesser figures represent better quality output
transformer.
3) Quality Factor figures derive from Total
Primary Inductance divided by Leakage Inductance. The higher
figures represent high inductance with low leakage. (better
quality)
4) Primary Capacitance causes the transformer to
resonate at certain frequency and also cause the anomaly frequency
response. The lesser figures are better.

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
(18Vp-p 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.

*See Frequency Response Graph Click
here

Model Picture

Brand

Silk Transformer

Model

S-325

Description

3K/20Watts output transformer with EI (M6) Lamination.
Although S-325 can not go as high as Tango XE-20S but comparable
to U-808. It has smooth waveform response. (No peak, No dip) With
its high inductance, S-325 also performs very well in bass region.
(see 40Hz waveform that tilt less than U-808)

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

See Graph Click here

Square Wave Picture

40 Hz

1 KHz

10 KHz

20 KHz

Model Picture

Brand

Tango

Model

XE-20S

Description

Universal output transformer with oriented hi-B cut core.
With hi-B core, the transformer has lower primary turn (Less
copper loss) than U-808 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

See Graph Click here

Square Wave Picture

40 Hz

1 KHz

10 KHZ

20KHZ

Model Picture

Brand

Tango

Model

U-808

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

See Graph Click here

Square Wave Picture

40 Hz

1 KHz

10 KHz

20 KHz

Model Picture

Brand

Audio Note

Model

Trans-152

Description

2.5K non-potted output transformer with M6 EI core.
Although it has small primary turn (around 1,800T-1,900T) due to
its large core size, TRANS-152 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

See Graph Click here

Square Wave Picture

40 Hz

1 KHz

10 KHZ

20KHZ

Model Picture

Brand

Golden Tube

Model

SE-40

Description

1.9K SE parallel output transformer extracted from Golden
Tube Audio model SE-40. 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

See Graph Click here

Square Wave Picture

40 Hz

1 KHz

10 KHz

20 KHz

Model Picture

Brand

James

Model

JS-6123HS

Description

Universal output transformer with EI core that performs
far behind Tango U-808. 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

See Graph Click here

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

See Graph Click
here

Square Wave Picture

40 Hz

1 KHz

10 KHz

20 KHz