DitheringFool
Head-Fier
I would highly recommend Feliks Echo. Dead quiet, elegant and solid build, and quality components. A really solid entry level OTL amp. The head-fi thread on this amp is pretty small and populated by tube noobs like myself and there aren't a huge amount of reviews available, though they are all very positive.
I've read on SABF that Feliks amps push the mids more upfront. I haven't heard their other amps, but I can confirm this does happen with the stock tubes on the Echo. This is a blessing when paired with VO, since it makes up for the VO's slight mids recess. I'm in the process of getting 6922 and 7308 tubes to roll instead of the stock russian 6N1P driver tubes.
You can either buy from upscaleaudio (the US distributor) or from Feliks directly, but possibly be subject to USD to EUR conversion and import/customs fees. These basically never get sold second-hand on head-fi or ebay. Take that for what it's worth.
When you are ready to tube roll. Check out these guides, among many.
https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html
https://upscaleaudio.com/pages/the-ultimate-guide-to-tube-rolling-introduction
Hope it helps!
Yup. The echo is just an amazing pairing to the VO. I can absolutely vouch for the stock tubes that come with it.