DIY output transformer test


       Ok, now I finished my DIY OPT. While waiting for my metal potting cup, I measure the performance of this small trannies.

   The first thing I test is the DC resistance, I got 115 ohm primary, and   0.58ohm secondary. Normally primary resistance of such a small trannies will be quite high, around 250 to 350 or even higher. Due to the c core's large window size, I can use thicker copper to reduce resistance.

  The AC impedance of this trannies ( at 1 KHz ) should be closed to what I intended to build, that is, 2.7Kohm. By connect a dummy load of 8.2 ohm at secondary, my LCR meter shows 2.737Kohm,  seems about right with my calculation here.





   The inductance is measured and seems a bit lower than expected, I use slightly thicker air gap spacer than calculated, this will greatly reduced the inductance. For impedance of 2.7k, 9.35 Henry of primary inductance can be consider acceptable, especially a small trannies like this which weight only less than 400 gram.




   For measuring leakage inductance, I short the secondary winding and measure the primary inductance again,  the LCR meter reads 2.92mH, which is much better than I expected.





   Check the sticker at the bottom of my LCR meter, the date shows that its time to send for calibration again. :(

  After all the static test, now its time to connect to my working tube amp and test the frequency response and wave form performance. I test it with my 6EW7 experimental PCB, with 2 watts of maximum output power.

  The measured frequency response at 1 watt RMS is from 24Hz to 53KHz at -1dB . I also measured it in full power of 2 watts RMS and it start from 34Hz to 42KHz, -1dB.  I keep measure the higher frequency at 1 Watt up to 100KHz and it drop to -4.0 dB. With this result, it consider acceptable for me. I actually aim for 40Hz to 18KHz @ -1 dB  at full power.


  Now its time for square wave test:

















And this is 40KHz !!



   Most of the single ended transformer can't give good square wave results.


After I compare with some commercial output transformer, I can say that this output transformer is perform far better than I expected.

  Listening test?  no need to tell much here, the efficiency is increasing, I can get louder and clean music, with better ambience and airiness. The bass for this small OPT is special , its fast and punchy , compare with other EI type OPT in my collection.


* I had just deleted the photos of square wave test result for Hammond and AN , I received the copyright violation warning :(.*