Metal-base and non metal-base 5AR4/GZ34?

The ones with the 'B' in the date code(ie: F32/B6H4), are from the Blackburn Plant. Personally; I found the double gettered type to be some of the most reliable and best sounding. A couple examples: (http://www.ebay.com/itm/Vintage-Mullard-Shield-GZ34-5AR4-2x-Halo-Getters-Stereo-Tube-f32-B2D2-2475-23-/181688527974) or (http://www.ebay.com/itm/Mullard-Blackburn-GZ34-5AR4-Double-OO-Top-Round-Getter-Rectifier-f32-B5K1-Tube-/161600624492)

I just can tell that when I had Carry SLP-05 and replaced original rectifier with Philips Miniwatt GZ34/5AR4 metal base nos 1957 I could not believe the difference it made. Yes, it was expensive move, but with great result.

I just bought one of these for my Modwright SWL9.0 se
http://www.upscaleaudio.com/philips-5r4gys-made-in-holland/
had to cut a hole in the cover to accomadate the size,but Im very happy with it. Got mine from a guy in Holland thru ebay for less $.