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Re: [Amps] Removing grid shorts

To: <>
Subject: Re: [Amps] Removing grid shorts
From: "Leigh Turner" <>
Date: Fri, 14 Jun 2019 09:48:18 +0930
List-post: <>
Hi Ron,

I tried a magnet on some old 811A broken internal electrode parts including
the grid basket and they stick to the there might well be scope
for correcting the electrode misalignment by the means mentioned
below....nothing to loose if the defunct tube is otherwise destined to

Agree with your comment about modern tubes like the now expensive 3CX800A
with grid to cathode shorts....a judicious placed lateral blow thud with a
soft plastic head hammer might work best with them as Roman US5WDX pointed
out on this forum, although the super magnet trick might still work it the
grid electrode is sufficiently magnetic.


-----Original Message-----
From: Ron Youvan [] 
Sent: Thursday, 13 June 2019 11:31 PM
To: Leigh Turner
Subject: Re: [Amps] Removing grid shorts

   Hi Leigh VK5KLT Turner:

> Although I've not tried it, a less dramatic technique here might work:

> If the tungsten / molybdenum wire welded into a basket forming the 572B's
> grid structure is sufficiently ferromagnetic or paramagnetic you might be
> able to achieve the requisite internal structural realignment by
> applying a neodymium super magnet cube towards the glass envelope.

> Careful visual inspection of the tube internals might first reveal in
> direction to apply the force so as to achieve a more symmetrical coaxial
> alignment between the grid and filament.

Which Metals Are Magnetic?

Magnetic metals include:

     Some alloys of rare earth metals

   Steel is cheep, most tube parts are made of steel, if that's not good
enough, copper or brass.

   The biggest problem is this thread is about modern "coaxial tubes"
like the:  "3CX800's with grid-cathode shorts." E-mail = 5/31/19, 08:46

   I think 572B's are too cheep to bother fixing and they do not have 
the problem that the modern "coaxial tubes" have.
   Ron  KA4INM - Understanding is much better than
                                       knowing how.

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