I have purchased 6n3 preamp from the Aliexpress vendor called "best partner mall", it regrettably arrived incomplete, without the mains transformer, despite the seller's product clear description stating the transformer will be included. The seller is totally uncooperative.
So beware folks - it may also happen to you. Now I have a useless piece of PCB with two valves sitting on it, as suitable transformers are not readily available where I reside.