OPT Characterization

[Le Thien Thanh]

Here are the parameters I measured of the OPT:
Primary DCR: 115R
Primary Inductance: 39H - 25Hz
Primary Capacitance: 2.7nF - 1Khz
Leakage Inductance: 18mH - 100Hz

 

[waltube]

Hi

Regarding the freq. answer I see more than 0,5 dB of variation.
Have you check the response at the end of 240 kohm resistor on grid of 300B?
Check the impedance of the probe of the test set.
If it is linear you can exclude te circuit, first of all
Then read the backward method to test only the trafo

Walter

 

[Le Thien Thanh]

this is the result i measured at the grid 300B

An externally hosted image should be here but it was not working when we last tested it.

 

[waltube]

This is reasonable

Try to test the OT only

Walter

 

[Le Thien Thanh]

so do you think the problem is in OPT.

 

[waltube]

Can you explain the test set? which generator and analyzer you use?
Try to measure the test signal comes from generator
Then, if you have a ss amp try to measure as described the OT only; it is not complicated

Walter

 

[euro21]

Try to omit negative feedback: 3k9.

 

[waltube]

to euro21
He said that no FB is used

Walter

 

[Le Thien Thanh]

Can you explain the test set? which generator and analyzer you use?
Try to measure the test signal comes from generator
Then, if you have a ss amp try to measure as described the OT only; it is not complicated

Walter

I Use keysight edux1002g

 

[Le Thien Thanh]

Here are the parameters I measured of the OPT:
Primary DCR: 115R
Primary Inductance: 39H - 25Hz
Primary Capacitance: 2.7nF - 1Khz
Leakage Inductance: 18mH - 100Hz

Leakage Inductance: 18mH - 100Hz ----- too tall ???

 

[Le Thien Thanh]

when i test the frequency. i hear hissing from OPT starting at 1Khz
Do you think due to the wire loops vibrating.

 

[Le Thien Thanh]

here is the OPT spec I made: 3K5 - 8R - 300B
EI 96 x 50 - 32 x 50 mm
P: 2160T - 0.3mm
S: 105T - 0.45mmx3
4S + 3P
S-S, P-P: 0.05mm PET
P-S 0.4mm Paper

 

[euro21]

The 39H a little unbelievable, this range is the 10k transformers territory.

With these "measured" OPT parameters the estimated OPT frequency range is -3dB 4.5Hz...32kHz.
If it not correspond with the screenshots the parameters are not completely correct.

If you test the amp with 10kHz square wave, the suspected resonance within the audio band would be more visible.

BTW the screenshot in the #203 post has similar tendency (with lesser gain) of FR than the output so the boost partially due the previous stages.

Try to measure FR on the grid of both stages.

 

[Le Thien Thanh]

i made measurement at 1Khz and 10Khz with square wave.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Le Thien Thanh]

this is the result of the main Inductance measurement at 100Hz : 29H
at 25Hz will be above 30H

 

[50AE]

By looking at the 10kHz square wave measurement, it is pretty good. The frequency response should be much better than the one you measured

Are the 10kHz square wave measurement measured under the same conditions as with the frequency response conditions?

 

[waltube]

I ask to describe the test set, which equipment are used

The range of dB on firsts freq. response are different from the lasts
And the response taken on grid of 300B is linear



Walter

 

[Le Thien Thanh]

below is the result i did it again.

10Khz square wave after OPT load 8R

An externally hosted image should be here but it was not working when we last tested it.

10Khz square wave at 300B . grid

An externally hosted image should be here but it was not working when we last tested it.

And the measurement results after OPT and at grid 300B.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Le Thien Thanh]

i use keysight edux1002g .
and this is the result measured at the grid 300B

 

[waltube]

To understand exactly the deviation from a reference point, 1 kHz (as 0 dB, is the standard) try to expand the scale, for example from + 2 dB to -3 dB
What I see is a good answer, the alteration is fraction of dB, maybe 0,2.

Walter