Hi Jim:
I can recommend one very highly. It's the Tung-Sol 5U4-G. Look only for the ones with these attributes:
1. ST-shape.
2. Top flash-getter.
3. Support rods between the plates.
4. Heat shielding material in the base.
You can copy and paste this link to see a photo of one (it shows everything but the top flash getter):
http://i27.photobucket.com/albums/c157/gerrye123/ts5u4g.jpg
They are getting hard to find, but it's not impossible.
Gerry