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Re: [Amps] Removing grid shorts

To: "'Alek Petkovic'" <>
Subject: Re: [Amps] Removing grid shorts
From: "Leigh Turner" <>
Date: Thu, 13 Jun 2019 10:28:24 +0930
List-post: <>
Hi Alek,

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 judiciously
applying a neodymium super magnet cube towards the glass envelope.

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



-----Original Message-----
From: Amps [] On Behalf Of Alek Petkovic
Sent: Wednesday, 12 June 2019 9:38 AM
To: Carl
Subject: Re: [Amps] Fwd: Re: Removing grid shorts

Ok. I see that you want me to think big.

I'll do it again and again until there are no more grid wires left. :-)

73, Alek.

On 6/06/2019 6:34 AM, Carl wrote:

> You give up after one try?
> Carl
> ----- Original Message ----- From: "Alek Petkovic" <>
> To: "Boye Christensen" <>
> Cc: <>
> Sent: Tuesday, June 04, 2019 7:47 PM
> Subject: Re: [Amps] Fwd: Re: Removing grid shorts
>> I had reason to test some unknown 572B valves yesterday. I tested 
>> them in an old Yaesu amp.
>> While I was at it, I thought I would try to fix a brand new 572B that 
>> has a G-F short. My supplier had already replaced the valve and 
>> didn't need the faulty one sent back. With an Ohmmeter, I determined 
>> which end of the filament the short was closest to. I then charged a 
>> 10,000uF capacitor with a 12V battery and discharged it across the 
>> relevant grid and filament pins. The fault cleared immediately. When 
>> I touched the leads of the capacitor together, after that, there was 
>> a good spark, indicating that there was still a lot of the charge 
>> left in it.
>> Well, I plugged the valve into the 2100 amp and switched on. The 
>> short immediately returned, as I could see that the plate current 
>> meter showed current draw without keying up.
>> So, with that particular 572B valve, the procedure did not work very 
>> well at all. Another display piece.
>> Cheers, Alek.
>> On 3/06/2019 11:08 PM, Boye Christensen wrote:
>>> Hi to all
>>> This is the normal life out time of tubes
>>> If the tubes is open after some time of warm up there might bee
>>> a change to repair !
>>> How to repair will bee  different of tube type (life time extended)
>>> But mainly it has to burn g1 - catode connection away !
>>> 73 Boye OZ7C
>>> -------- Forwarded Message --------


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