ABM- From what I see it looks like it could be used. I would give it a few days until some of the more knowledgable chime in. I'll keep a watch on this post but it looks ok. What got you setting your sights on this tube? Happy listening, Chris.

Hey ABM, this tube can be used in the ZP3. Nearly all 5 volt rectifiers can be used in the ZP3 (5AR4, 5V4, 5U4, and 5Y3, and most related variants). The exception is some 274b tubes may not be compatible, but I haven’t heard of anything else. The CV593 is equivalent to a GZ32, which I believe is equivalent to a 5V4G.

I’ve used the Mullard CV593 in my ZP3, and it’s a great rectifier. It brings out a very warm, spacious, and dimensional sound. My favorite rectifier in the ZP3 is a 50s RCA 5Y3GT, but I didn’t like this tube in my CSP3 or SE84UFO. The CV593 was excellent in both the SE84UFO and CSP3. I’ve found the rectifier to make a huge difference in the ZP3, so you’ll have to see what you prefer. In my experience, the 5Y3 gave the tightest sound, while the tubes with lower voltage drop (5AR4, 5U4) had a larger sound with longer decay.