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Old 16th Jun 2019, 7:46 pm   #1
David Church
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Default GZ32 rectifiers for a quad amp

I have just replaced some of these in my quad II's and looking around I see that there is a bit of mumbo jumbo about these rectifiers with regard to the shape of the getter.

Its round or a D shape.

Anyone know what that's about? Is it just snake oil?
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Old 16th Jun 2019, 7:47 pm   #2
M0FYA Andy
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Default Re: GZ32 rectifiers for a quad amp

Totally unadulterated snake oil!
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Old 16th Jun 2019, 7:55 pm   #3
David Church
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Default Re: GZ32 rectifiers for a quad amp

OK Andy but I heard the D getters

A. Pushed the electrons forward in a tighter pattern?
and
B. Stopped any out of phase electrons from causing intrinsic vibration?

Unless you have clear science to prove my Gran wrong then you can't really make such a definitive statement (or can you?)
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Old 16th Jun 2019, 7:58 pm   #4
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Default Re: GZ32 rectifiers for a quad amp

If you have both you are in a prime position to tell us which sounds better!
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Old 16th Jun 2019, 8:21 pm   #5
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Default Re: GZ32 rectifiers for a quad amp

Recta-guru folklore has it the D getter works better, but they must be parallel to the nearest Ley Line for the best sonic stability, whereas the round ones will cause a massive disturbance in the space-time continuum and will no doubt cause the sonic image to become far less stable, in fact round getter GZ32ís were not used in the first TARDIS due to this stability problem.

There have been instances where a metal base GZ34ís has been fitted to Quad IIís, sadly this caused such a massive disturbance in the space-time continuum the listener disappeared up his own worm hole to another dimension

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Old 16th Jun 2019, 10:47 pm   #6
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Default Re: GZ32 rectifiers for a quad amp

Would the BVWS Membership Secretatry be winding us up, perchance?
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Old 17th Jun 2019, 1:26 am   #7
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Default Re: GZ32 rectifiers for a quad amp

Getters are no longer active. They have done all of their job before the valve ever left the factory. They were the storage structure for the chemically active metal which is now plated onto the inside of the glass. The shape of the deposited metal is more likely to have an effect than the shape of the spent getter loop!

Perhaps taking a valve to a palmist to have the shape of its getter deposit read could be the next big thing.

David
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Old 17th Jun 2019, 5:20 am   #8
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Default Re: GZ32 rectifiers for a quad amp

Despite, or maybe because of, all the hilarity in this thread, I have learned something new: I had not heard of a 'getter' before this, but have not had anything to do with thermionic valves apart from basic 'Scroggie'. Where does this name come from? It seems that the structure should be called a 'giver'.
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Old 17th Jun 2019, 7:40 am   #9
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Default Re: GZ32 rectifiers for a quad amp

While pondering the obsession with getter structure that exists in some circles, it occurred to me that it might not be quite as daft as it seems.

Getter shape and position did sometimes vary between different eras and manufacturing plants within the production life of a valve. Therefore, these getter parameters can be used as convenient markers of other, more important changes in the production that are invisible to the naked eye. For example, if the line that used a D-getter also produced a more accurate grid wire spacing, the D-getter examples might be more linear and hence technically better valves. Once such a correlation is discovered, the getter or print style or other visible indicator becomes synonymous with the electrode structure improvement.

This is perfectly reasonable but open to misinterpretation by the less technically savvy, who might assume there is a causative relationship, i.e. it is the difference in getter assembly itself that makes one valve better than another, prompting them to seek out certain versions of getter in valves where no correlation exists with genuine improvements.
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Old 17th Jun 2019, 9:13 am   #10
M0FYA Andy
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Default Re: GZ32 rectifiers for a quad amp

A question of semantics to clarify, please. I regard the 'getter' as the material which is evaporated to absorb residual gas molecules, and the tray structure used to hold this material before firing as the 'getter tray'.

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Old 17th Jun 2019, 9:28 am   #11
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Default Re: GZ32 rectifiers for a quad amp

The "getter" simply "gets" hold of the stray gas molecules when it's activated or flashed off by heating.
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Old 17th Jun 2019, 9:49 am   #12
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Default Re: GZ32 rectifiers for a quad amp

One area where getter frames/bowls can have a distinct impact is in the microphonic response of, usually, small-signal valves. They are part of the acoustically resonant mechanical structure after all. This is wholly irrelevant to rectifiers of course.

With reference to David's comments about getter inactivity and the shape of the film deposit, I always thought that the getter referred to the metal film itself, and that does remain active, continuing to absorb gas through the valve's life.

Palmistry on the film deposits can give some indication of a valve's history. The picture shows three GZ32s from my collection. I'm as sure as I can be that the left-most one is unused (spotless shiny glass and base, pristine printing, in un-torn paper and corrugated wrapping inside an undamaged box). The top of the glass envelope shows no sign of metal deposits on the inside. The other two valves have had some use. They both have silver patches above the cathode tubes, the ones on the middle valve being quite small and distinctly cross-shaped, those on the right-hand being larger and more circular blobs. I'm not sure where this metal has come from. There are no getter frames above the top mica, the heater wire is coated in ceramic insulation (which had better not be porous to metal vapour if it's going to remain as an insulator), the outside of the cathode tube is coated in metal oxides, which just leaves the inside of the tube and I understood that that was made of something refractory (nickel ?). I do believe though that the presence of this metallisation indicates that the valve has been used. You might want to raise an eyebrow if someone tries to sell you an 'unused new old stock' GZ32 with such deposits on it.

Cheers,

GJ
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Old 17th Jun 2019, 11:36 am   #13
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Default Re: GZ32 rectifiers for a quad amp

I have always assumed (and thus might be completely wrong) that these deposits are tungsten from the ends of the heater hairpins, where the coating is probably breached or porous. I have not given thought to whether any such deposit occurs onto the coating itself and whether it has any impact on HK insulation.

And yes, describing the getter tray or ring simply as the getter is a bad habit that I have perpetuated above. The getter is specifically the deposited film.
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Old 17th Jun 2019, 2:03 pm   #14
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Default Re: GZ32 rectifiers for a quad amp

The only time a getter (holder)? affected the operation of a valve is when it fell off! Many years ago I did have a valve with an intermittent short caused by the getter floating about inside. Careful movement of the valve allowed me to move the offending piece down into a position where it didn't cause problems and the set worked for years.....as long as it was moved carefully...….
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Old 18th Jun 2019, 1:31 pm   #15
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Default Re: GZ32 rectifiers for a quad amp

Thanks Chris (Herald), I assumed the purpose was to deposit the metallic film at the top of the valve- I did say that I knew nothing about the theory and operation of these mysterious objects! I will read further...
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Old 18th Jun 2019, 1:52 pm   #16
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Default Re: GZ32 rectifiers for a quad amp

I've just had a look at a GZ37 used for testing/experimental purposes and I see that it has the silver deposits on the glass at the top of the valve just the same as in the GJ's post #12. The orientation is different in this valve and the two square silver deposits are in line with the square holes in the top mica support, the getter is at the bottom of the valve. I think I have a couple more of these in the loft, but can't remember if they're used or unused and they're too awkward to get to in order to have a look at to confirm just at the moment.

The first photo below shows the two square silver deposits on the glass. The second photo shows the two holes in the mica top support from below. The last photo shows the getter at the bottom of the valve.
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Old 18th Jun 2019, 2:25 pm   #17
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Default Re: GZ32 rectifiers for a quad amp

Interesting. I think the cathode tubes are directly below the square holes in the mica aren't they ? It's as if the metal vapour is leaving the cathode tubes and passing to the glass through the square 'masks' in the mica. The mica is there as a mechanical support for the valve's separate electrodes. These need to be insulated from one another, obviously, and efforts were made, in some valves at least, to keep the getter film off the micas to avoid compromising their insulation. It looks like there would have been metal on the GZ37 mica around the edges of the square holes in this case though.

Cheers,

GJ
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Old 18th Jun 2019, 2:33 pm   #18
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Default Re: GZ32 rectifiers for a quad amp

You'll find that transmitting valves have no getter. Because of the high voltages involved, the manufacturers didn't want the risk of vaporized metal being sprayed around and any getting onto any insulators.

So they were subjected to a diffusion pump to take them right down to a very low final pressure, and kept there for some time to allow outgassing to proceed before they were sealed off.

Receiving valves got brought down with a rotary pump, allowed to outgas, sealed and then the getter was fired and the exposed reactive metal brought the pressure down the rest of the way. The getter ring was made of channel-shaped high melting point metal and the channel filled with the reactive metal. The whole lot was then plated with non-reactive metal to seal it so it could be stored and handled in air.

Once fired in the sealed valve, the non-reactive plating (usually nickel) boiled off first, before releasing the reactive stuff. So looking ath the glass bulb of a finished valve, you see the nickel alloy against the glass. The reactive stuff forms the inner surface, flypaper for any itinerant gas molecules.

As G-J says, changes to getter loop shape and paint colour may well have happened at the same as other changes... changes which might matter.


David
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Old 18th Jun 2019, 5:40 pm   #19
David Church
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Default Re: GZ32 rectifiers for a quad amp

Well just for fun I tried all the GZ32's today in my Quad II's. The only difference I heard between any of them was when I turned the volume up

Have to say though my solid state power amp is at least as good as the Quads (to my ears.)
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Old 18th Jun 2019, 5:47 pm   #20
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Default Re: GZ32 rectifiers for a quad amp

Quote:
Originally Posted by David Church View Post
... Have to say though my solid state power amp is at least as good as the Quad's (to my ears.)
Peter Walker would be pleased (all good quality hifi amps operating within their specified limits should sound the same ).

Cheers,

GJ
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