Converting tube preamp from 110v to 230v

It all depends on the manufacturer and sometimes also the model. Some can, some can't be rewired.

It depends on whether you have a dual wound transformer. If not the proper way is to change the transformer. A step down transformer will degrade the sound.

Not sure if a step-down transformer will degrade the sound with the particular preamp, but I would expect that there is less likelihood of degradation using a transformer with a preamp, that draws an essentially constant amount of current all the time, than for instance with a Class AB or Class D power amp, where the current draw fluctuates widely with the dynamics of the music.

A transformer might even improve sonics, by filtering out high frequency noise.

Also, I believe the AC in your country is 50 Hz. Although that most likely won't be an issue, you would want to confirm that the preamp you select is rated for 50 Hz as well as 60 Hz operation.

Regards,
-- Al

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