output transformer testing and measurement

[fazildiken]

Hi,
How to measure and test the output transformer of the tube amplifier with signal generator and oscilloscope. How should the connections be. Can you share any videos or documents.

 

[Bandersnatch]

Should be done with power. Amplifier, through a source resistance to the secondary, and load the primary with its design load. Apply a voltage ( 2.83 V rms ) to the 8 Ohm secondary and measure response of the primary. Suggest a calibrated voltage divider so as not to run primary voltage too high. Resistor rating will determine how long you can do this. Suggest a solid SS amp to drive the secondary/speaker side. Source resistance equal to the tap, and measure input voltage at the amplifier terminals, not the OPT's.

Is not perfect, but it is the improved method one gent( who did go to the trouble of publishing a pile of OPT tests) came up with me.

Douglas

 

[waltube]

Thread 'OPT Characterization'

2017-10-24 5:49 pm

In attach some rests published on Audioreview magazine about three trafos

In Fig. 1 the test set
We check the trafos putting the signal from a SS amp to the secondary then measuring the results on resistive partitor.
There isn't the bias current because we haven't measured significative difference with it. I have sent the tests in other thread

Impedances
With a new software by Fabrizio Montanucci of Audioreview is possible to see the plot of impedance vs frequencies.
The primary ( now the secondary, in this configuration) is open and the secondary ( now the primary) is connected with a...

• waltube
• Replies: 228
• Forum: Tubes / Valves

walter

 

[sajadho1988]

If you have a good soundcard, you can use REW software with accurate results:

This is how I measure frequency response of my handmade OPTs. RL should be equal to nominal secondary impedance, and for measuring FR adjust the signal for 1W to max output power across secondary. THD will be measured at the same time.

The DC bias switch is for adjusting the air gap of SE OPT's and should be open in any other test.

 

[sajadho1988]

I forgot to add primary load; There should be a resistor equal to nominal Zp or plate resistance of the driver tube connected across primary winding, so here is the correct diagram:

Also for measuring impedance and shunt C and leakage inductance use this:

Foe measuring impedance, the excitation voltage should be the max possible voltage of headphones output, also bear in mind that impedance measurement is at low signal so it won't show anything about low F response and primary inductance, but it will show overall shunt capacitance (measured at 20KHz with open secondary), and also leakage inductance (measured at 1KHz with closed secondary).

 

[trobbins]

Do you not have a tube amplifier ?