couldn't resist to connect the Sowter 9351 Headphone Output Transformers to my (original) tu-05 to listen how they sound - one word - Un Be Lie Va Ble ....
i tested different tubes,RFT97 and Telefunken Diamond Base Berlin made DF96 combined with the TEN 3s4 and the PHILCO 1s4 with my DIY Grado Style Headphone and (SIC!) the HD800.
The HD800 (300 Ohm Impedance Setting of the output transformers) together with the Telefunken DF96 - TEN 3s4 is a match made in heaven, for my DIY Grado i prefer the RFT DF97 - TEN 3s4 combo.
Most remarkable listening with the Sowter transformers is not only the overall sound quality but the soundstage depth and added information of the space, how to say, you not only have this feeling of depth in the middle of the "soundstage", but also on the left and on the right, listening to Telarc, Erich Kunzel, Tschaikowsky 1812, you have the feeling to really see the orchestra in all its dimensions, located at a square formed area in front of you, exactly beeing able to draw an image of that area with all the positions of all the instruments, the choir, always beeing able to tell who is in front and who is behind or second or third on the left, right, in the middle.
Verdi, Requiem, 2. Dies Irae, the impact of the drums on the left is unbelievable precise, deep, really hits,
The efficiency of the transformers is outstanding. listening to 1812 with the integrated tu-05 transformers i must set both colorfly c4and tu-05 to maximum volume while with the Sowter transfomers the same output level is reached with adjusting the tu-05 to about 60 to 70%.
have to spend some more time to listen to the Sowter 9351 output transformers also testing the different impedance settings, but even now i am sure that this is again one step up the sound quality ladder, and best of all this transformers cover everything from 30 to 600 ohm output impedance.