[Amps] Fwd: Re: Removing grid shorts

Wed Jun 12 19:30:44 EDT 2019

Hello Alek,

 Wednesday, June 12, 2019

 As  an  ornament it will still be as beautiful, but you may get lucky
 and it will return as a functional tube. nothing ventured.... ;)

Best regards,
 Chris    2E0ILY       mailto:chris at chriswilson.tv

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

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

AP> 73, Alek.

AP> On 6/06/2019 6:34 AM, Carl wrote:
>> You give up after one try?
>>
>> Carl
>>
>>
>>
>> ----- Original Message ----- From: "Alek Petkovic" <vk6apk at bigpond.com>
>> To: "Boye Christensen" <oz7c at cool.dk>
>> Cc: <amps at 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 --------
>>>> Subject:     Re: [Amps] Removing grid shorts
>>>> Date:     Sun, 02 Jun 2019 15:29:40 +0800
>>>> From:     Alek Petkovic <vk6apk at bigpond.com>
>>>> To:     n2ic at arrl.net
>>>> CC:     amps at contesting.com, Steve London <n2icarrl at gmail.com>, 
>>>> ve5ra at sasktel.net
>>>>
>>>>
>>>>
>>>> Yeah, my local club has a GU84B with the same condition. No short 
>>>> when she's cold but a couple of minutes into the warmup, the belly 
>>>> ache starts and stays.
>>>>
>>>> The tube is a display piece.
>>>>
>>>> Cheers, Alek.
>>>> VK6APK
>>>>
>>>> On 31/05/2019 8:46 PM, Steve London wrote:
>>>>> I am the "proud" owner of two Alpha 3CX800's with grid-cathode 
>>>>> shorts that start 2 minutes into warm up. I would be thrilled if 
>>>>> they cleared themselves after 6 minutes of warm up.
>>>>>
>>>>> 73,
>>>>> Steve, N2IC
>>>>>
>>>>> On 05/30/2019 07:27 PM, Doug Renwick wrote:
>>>>>> Let's see if this e-mail goes through at Amps. It didn't go 
>>>>>> through at
>>>>>> Ham_Amplifiers.
>>>>>>
>>>>>> Jim,
>>>>>>
>>>>>> I am not sure what to try next. Others have said not to use a 12v car
>>>>>> battery for this tube. So I am at a point of scraping the tube.
>>>>>>
>>>>>> It works fine if it is allowed to warm up for over 6 minutes. The 
>>>>>> short now
>>>>>> lasts from about 2 min to 5 1/2 min after turn on.
>>>>>>
>>>>>> Doug
>>>>>>
>>>>>> "The difference between stupidity and genius is that genius has 
>>>>>> its limits."
>>>>>> Albert Einstein
>>>>>>
>>>>>> -----Original Message-----
>>>>>>
>>>>>> <I have a GU-78B that has developed a grid short. I have 
>>>>>> determined the grid
>>>>>> <short initiates about 2 minutes after power on and ends after 
>>>>>> about 5
>>>>>> <minutes.
>>>>>>
>>>>>> <I have tried unsuccessfully to 'burn' the short by hooking up a 
>>>>>> 560?f
>>>>>> <capacitor fed with 300vdc.
>>>>>>
>>>>>> <What other methods that can be tried to 'burn' this short?
>>>>>>
>>>>>> <Doug
>>>>>>
>>>>>> ## I assume you mean the control grid....and not the screen grid ?
>>>>>>
>>>>>> ## If it is the control grid...... Im assuming the control grid is
>>>>>> shorting to the cathode ? Or is the control grid shorted to the 
>>>>>> screen
>>>>>> grid ?
>>>>>>
>>>>>> ## 560 uf cap charged up to 300 vdc = 25.2 joules. Thats not a lot
>>>>>> of energy.
>>>>>>
>>>>>> ## What happens after 5 minutes..and the short vanishes? Is the tube
>>>>>> now useable ??
>>>>>>
>>>>>> ## watch out, the control grid dissipation is no doubt very 
>>>>>> little, as
>>>>>> whats indicated on the spec sheet. In your quest to burn the short 
>>>>>> out,
>>>>>> you could destroy the control grid in the process.
>>>>>>
>>>>>> ## folks who have had control grid to cathode shorts on a 3-500Z, 
>>>>>> have
>>>>>> typ a 50% chance of burning the short open... using a 12 vdc car 
>>>>>> battery,
>>>>>> which will supply a LOT of current. Depending on the ESR of your 560
>>>>>> uf cap, the ESR will limit the current somewhat. Typ 560 uf @ 450
>>>>>> vdc
>>>>>> lytics have a ESR of .203 ohms..... which is low enough to deliver 
>>>>>> a lot
>>>>>> of current... albeit for a split second.
>>>>>>
>>>>>> Jim VE7RF
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>>>>>>
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>>>>> _______________________________________________
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>>>>>
>>>>
>>>
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>>>
>>>
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