@cbrez
I bought my MicroZOTL preamp lightly used and a little over a year old. The previous owner said it came with Trigon 12AT7 tubes. I tried them and didn't like them. He had purchased some Telefunken tubes {not cheap} and I bought them with the preamp. I've also tried Philips, Siemens, and Brimar Yellow T. Siemens came in a close second to the Telefunken. These are all 12AT7 type tubes.