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.
Cheers,
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Alek Petkovic
Sent: Wednesday, 12 June 2019 9:38 AM
To: Carl
Cc: amps@contesting.com
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" <vk6apk@bigpond.com>
> To: "Boye Christensen" <oz7c@cool.dk>
> Cc: <amps@contesting.com>
> 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.
>> VK6APK
>>
>> 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 --------
++snip++
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