I have tried the EH (steel and gold pin), JJ, late 60's Siemens cca, some Chinese tube, Siemens 7308 in my DK VS-1 integrated amp. The original Chinese tube was similar to sound of Sovtek in some other equiptment Ive heard, only somewhat more "grainy", but with an even amplification of all frequencies. The 7308 was a bit dull compared to the others with uneven presentation of harmonics. The cca had a tendency to exagerate higher frequencies at expense of mid-range. The steel pin EH had a slightly exagerated volume to middle frequencies while the gold pin had a bit more exagerated volume to mid freq extending into the upper frequencies. The JJ's have a more even-handed amplification of all freq without unusual harmonic deficit, over all presentation similar to Telefunken. The DK does not have the resolution that some preamps have so your results may vary according to aplication. I've heard the above tubes in other stuff but not directly compared but very generally same results. Good luck and please let us know how it all turns out, Mike.