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Author Topic: Tube shields on EL-84's  (Read 93 times)

galaxiex

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Tube shields on EL-84's
« on: May 07, 2018, 09:04:41 PM »

Does anyone use tube shields on EL-84's?

I've been working on this amp and noticed that the EL-84's seem to radiate a LOT more heat than the 12AX7's.

It's seems like the heaters in the EL-84's get very hot compared to the 12AX7's

Before noticing this extra heat, I saw some extra tall tube shields that will fit the EL-84's.

So I ordered some thinking to use them more for tube retention than shielding.

I'm concerned that they may trap the heat and shorten tube life.
Am I way off base here? Will it matter at all?

I know there are wire tube retainers for these tall 9 pin tubes,
but the amp has those bases made for shields just like the 12AX7 tube and I thought to put them to use.

AFAIK this amp never had retainers at all for the EL-84's.

Should I even bother?
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Enzo

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Re: Tube shields on EL-84's
« Reply #1 on: May 07, 2018, 11:24:20 PM »

One rarely has the need to shield power tubes.  There are larger size preamp tubes - same shape as power tubes - that do need shields.  That is what they are for.

Are your tubes falling out?

It isn't the heaters inside the tubes making them so hot, it is the action of the power tube doing it.
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galaxiex

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Re: Tube shields on EL-84's
« Reply #2 on: May 07, 2018, 11:37:30 PM »

No, actually the sockets are very tight.
It's a bit of a struggle to pull them.
I do use a rocking/rotating motion to remove them.

I suppose I just liked the idea of retainers since they do hang upside down when in use.
I'll not bother with these, if my OCD nags me into retainers I'll get the wire type.
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tonyharker

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Re: Tube shields on EL-84's
« Reply #3 on: May 08, 2018, 05:17:18 AM »

Don't use shields on power tubes like EL84s, you will only shorten their life and maybe overheat them.  Shields should only be used in preamp tubes where they are likely to pickup RF.  So hi gain hi impedance first stage amplifier tubes only. Tube retainers ie spring clips can be used on any stage.
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