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Old 23rd Oct 2020, 11:45 am   #1
mpegjohn
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Default Mounting a PL509 horizontally

Hi,
I am going to use a PL509 as a variable voltage source.
I would like to know if it is possible to mount these very hot and large valves horizontally.
If so is there any particular way around they need to go.

Thanks,
John.
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Old 23rd Oct 2020, 12:07 pm   #2
ms660
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Default Re: Mounting a PL509 horizontally

Horizontal should be no problem but maybe support the top end of the valve (the top cap end):

https://www.radios-tv.co.uk/wp-conte...TT-INNARDS.jpg

That TV in the link is normally operated with the chassis in the vertical position, so the PL509 etc will be horizontal.

EDIT: Link added.

Lawrence.

Last edited by ms660; 23rd Oct 2020 at 12:21 pm.
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Old 23rd Oct 2020, 12:55 pm   #3
GrimJosef
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Default Re: Mounting a PL509 horizontally

The general rule is that where the grid is wound around two quite widely spaced rods, so the resulting spiral is very much 'racetrack' shaped, the valveholder should be positioned so that the long direction of the racetrack is vertical. That way if the thin grid wires get hot they won't tend to sag, under gravity, in a direction which brings them closer to the other electrodes.

Cheers,

GJ
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Old 23rd Oct 2020, 1:02 pm   #4
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Default Re: Mounting a PL509 horizontally

The infamous Pye 697 chassis had the PL509 horizontal. No idea if the design took into consideration grid alignment but I had little problem with the valve in that chassis. Enough other problems though.
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Old 23rd Oct 2020, 1:22 pm   #5
mpegjohn
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Default Re: Mounting a PL509 horizontally

Thank you all.
Horizontal it is then Taking care to position it correctly.

John
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Old 23rd Oct 2020, 1:49 pm   #6
Marconi_MPT4
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Default Re: Mounting a PL509 horizontally

Mullard advise in their technical literature that for indirectly heated valves with high mutual conductance, the first grid major axis should be vertical. This would apply to PL509.

Rich
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Old 23rd Oct 2020, 3:08 pm   #7
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Default Re: Mounting a PL509 horizontally

They are used horizontally in all sorts of designs, but I don't like it!

I had to replace one that was mounted on its side in a linear amplifier a few months ago, due to it going to air from its 'supported' top cap. I've also seen unsupported ones crack from a base pin due to, I suppose, heat and stress. I think there's a lot of luck involved in it and the above cases may have just been coincidences, also they all involved the 6 volt and higher current heater version which is the EL509 and sometimes the 6KD6.
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Old 23rd Oct 2020, 10:38 pm   #8
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Default Re: Mounting a PL509 horizontally

They're probably run quite hard in linears. Active air cooling might be justified.
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