5y3/5z4

[jim_jobe]

These have virtually identical specs and are interchangeable so why does the 5Z4 have separate cathodes? What's the advantage?
Jim

[murphyv310]

The 5Y3 is a filament valve, the filament is in effect the cathode, they warm up virtually instantaneously thus charging the smoother very quickly and increasing surges.
The 5Z4 is an indirectly heated cathode valve and has the advantage of a longer warm up time, in a radio etc the other valves will be ready to conduct at the same time as the HT is available after switch on this is much easier on the smoothers with little or no surge.

[G4XWDJim]

I often wonder about the life of the electrolytics when operated under these two different sets of conditions.

When the other valves are cold and not conducting does the 5Y3 or a silicon rectifier exercise the cap through its range of voltage and benefit it, providing it doesn't exceed it maximum, or will the cap have a longer life when its voltage comes up slowly and doesn't reach its maximum, as if with a 5Z4 or other rectifier with a cathode.

When reforming an electrolytic you try to get it up to its full rated voltage, so, in actual operation in the case above could that be what the 5Y3 is doing and benefitting it.

Jim

[murphyv310]

Jim.
Look at it this way, most AC sets with an AZ31, 5Y3, or AC/DC sets with selenium, or silicon rectifiers will have had one or two sets of smoothers in their lifetime (I changed hundreds in the 70's) but those fed from a 5Z4 or a GZ32 etc were often are on their originals.
A set that has been off for many years may suffer cap failure any way due to being idle no matter what rectifier is used.

[JHGibson]

A rectifier with two independent diodes can be used in a voltage doubling circuit.
John.

[ricard]

True, but the 5Z4 doesn't have separate cathodes; they are connected together (mechanically they could be one, although the 5Y3 has internally separate diodes, unlike valves like the EZ80 which have one long cathode with two anodes after each other; I don't know what the 5Z4 looks like internally), and one side of the filament is also connected to the cathode, thus the cathode are not insulated from the filament as in most indirectly heated valves.

On the other hand, this means that the 5Z4 is pin compatible with the 5Y3. I wonder if that was the intention?

/Ricard

[GrimJosef]

Originally Posted by ricard

I don't know what the 5Z4 looks like internally

It looks like this http://r-type.org/exhib/aaa0094.htm

Cheers,

GJ

[ricard]

I did check the National Valve Museum but stopped looking when I came to the metal-enveloped 5Z4 version ... should have looked further ... thanks for the link. Looks like internally it is made up of two separate diodes then, like the 5Y3.

/Ricard

[jim_jobe]

Thanks Trevor et al for your very clear explanations. I'll remember not to sub a 5Y3 in future now!
Jim

[Peter.N.]

Pretty well all international octal valves of a given type had the same pin out's, so you could fit all sorts of 'inappropriate' valves and they would work - after a style. This 'standardisation' proved very helpful in servicing.

Peter

[GrimJosef]

Originally Posted by ricard

Looks like internally it is made up of two separate diodes then, like the 5Y3.

Two separate electrode assemblies, yes. But the cathodes are wired together inside the envelope. They both come out on the same pin - no 8.

Cheers,

GJ