Converting tube preamp from 110v to 230v

If the preamp has multiple primary windings on the power transformer, it's simply a matter of moving or using jumpers to wire the primary to 220Vac. Using an external transformer for this purpose would degrade the sound and therefore would not be advantageous. You could potentially have the power transformer replaced provided the manufacturer still has them. Most companies these days only fit a single primary winding on their products to guard against U.S. Dealers shipping product over seas and vice versa. They have to protect their distributors and dealers financial interests.

Many thank for all the responses. My query was prompted by a spate of high end ARC preamps for sale on Agon. I guess there are no shortcuts...!
Have a great XMas
Pradeep

HiFigeek is correct. I have often bought in the US and imported to Europe. Only had a problem once with an integrated amp. Manufactureres make for a world market, by and large they have to design a product that is easily changed.
The CJ Premier 17 I bought some years ago, took 20 minutes to change the transformer taps to convert to UK voltage. I am sure some products are more difficult, so do a bit of research if you can.
I know of one poor individual who bought a transformer for an expensive Spectral amp. When he took the lid off, there was a simple switch inside to change the voltage Doh....

This story has a happy ending. Bought a used 110v CJ GAT on Agon . Asked CJ for wiring instructions. Lew Johnson graciously sent the diagram etc. Conrad Johnson is a fantastic company to deal with and Lew is a true gentleman , always a pleasure and ever mindful of his customers. This is so unlike that other tube company which simply refuses to have anything to do with voltage conversion.
Many thanks to all of you who chimed in.
Cheers
Pradeep