Taiwan R.O.C.: Innovation patent no.I703815
USA: US 10,218,320 B1
China: Innovation patent no. ZL 2018 1 0972720.2
Regarding the vacuum tube power amplifier, mostdesign engineers know that the key charactersare must be with a highly magnetic flux density, low magnetic losses, sufficient inductance and the low internal resistance losses to ensure the flat response of vacuum tube power amplifier keep at 20Hz~20KHz.The flat response means that the frequency response can be kept flat within the frequency response range of 20Hz~20KHz.The HI-FI flat response specification is from the starting point 20Hz to the end point 20KHz +/-3dB.
In the early 30~50s, due to the excessive carbon volume of the silicon steel sheet material, the frequency response is always between 45Hz to 16KHz, which is still far away from the standard requirement, but now, the silicon steel Z11 (35Z155 or 35JG155) or the low-carbon of large audio transformer is capableto reach the HI-FI standard at 20Hz ~ 20KHz, which also let the timbre of the vacuum tube come into play extreme, and enter the High End hall.
It's a mission impossible to accomplish without these advanced materials and costly resources, that's why the price of vacuum tube amplifiers are always expensive for most people. Most design engineers are familiar that the audio output transformer is the most critical component in addition to the vacuum tubes, of course there are so many different options or backup solutions available to select, but designers understand that the wrong choice will result in poor frequency response, and make the product un-commercialized, unable to be put into production, unsold, or even irremediable. Therefore, the material of the audio transformer is not an optional component.