In truth you are much better to let an expert build it .
Radu Tarta has been building SET amps. And DHT preamps
for many years ,knows many secrets that only an expert
with tubes would know. And his prices are not that much more then you can build it yourself .there are just so many things that can go wrong . The cost of the chokes ,and transformers are by far the most expensive part of the build just check his name out in CT .he builds for the Love of the build ,profit is not his main goal.
he has built many amps,preamps for myself and others .well worth your time to consult with him.