anyone got a decent one they want to flog ?
Possibly. I will have a look, later on.
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No, sorry.
I think I gave them to the person, who bought my preamp, some time ago.
never mind thanks for looking
Demand is huge and supply, while not daftly limited, is such that the market price is what it is (painful). I have a mate who restores vintage test gear and he fairly regularly comes across GZ34s in that. They became Mullard’s stock rectifier from the late 1950s onwards so were used in loads of fairly unlikely things where an EZ81 wouldn’t quite cut the mustard.
VB
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I assume a Mullard GZ32 is of no use?
This any use?
Thanks Rob but no
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I have a tad in at the mo, just want to have a listen to others whilst I have time for house move wait. Cv378 on its way
I assume your amp can cope with the 3A heater demand of the GZ37?
Probably not!
Although the blurb says yes
much nicer than a GZ34 imho 
The 5Z4P rectifier tube can be replaced by the 5Y3 family, U50, U52, U54, 5U4G, CV378, GZ34, 5Z4, 5T4 , VT-117, VT-74 or 5AR4 directly.
im hoping
What amp is it for?
Very different valve though, and not just in the heater. Late production GZ34s would drop less than 10V at 100mA (one diode) - the graph from 1958 says just 8.5V ! By contrast the 1958 datasheet for the GZ37 says it drops more than 24V.
The GZ37 is also shown being used with a very small reservoir capacitance - just 4uF. I imagine it will cope with a good deal more than that, especially if the mean current isn’t high, but I don’t know how much more. The GZ34’s good for 60uF though.
VB
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Yes HT usually a fair bit lower from a GZ37
I never suggest they are the same, they are quite different as you so clearly set out, but I prefer the gz37
Yup, datasheets reckon that with a 400-0-400V supply and a capacitor input filter the GZ37 will give you 410V DC at 150mA whereas the GZ34 will top 465V.
VB
Indeed, and it is a part if what the op will hear when he fits it.
The difference between tube rolling and circuit design