[Amps] Holding a vacuum

[Carl]

 A small fan is fine.

Carl
KM1H



----- Original Message ----- 
From: "Pete N4KW" <n4kwpete at centurylink.net>
To: <amps at contesting.com>
Sent: Friday, November 28, 2014 10:43 AM
Subject: Re: [Amps] Holding a vacuum


> Earlier this week I emailed Eimac with the question about shelf life of 
> the new 4CX1500B tubes that I have.  I also asked about the serial 
> number on the tubes and how to read it.
> I am awaiting the code for the serial number, regarding shelf life they 
> recommended that I at least apply filament voltage every six months.  If 
> one was to apply filament voltage would a blower be required or not for 
> this tube.
> 73 Pete N4KW
> 
> 
> On 11/27/2014 3:24 PM, Carl wrote:
>>
>> ----- Original Message ----- From: "Bill Turner" <dezrat at outlook.com>
>> To: "Amps group" <amps at contesting.com>
>> Sent: Wednesday, November 26, 2014 11:08 AM
>> Subject: [Amps] Holding a vacuum
>>
>>
>>> I'm curious as to your experiences with tubes in long term storage.
>>> The question is, which type holds a vacuum better - glass or ceramic,
>>> or is there no difference?
>>>
>>> My own limited experience says ceramic is better, but that is only
>>> with a few tubes.
>>>
>>> All comments welcome.
>>>
>>> 73, Bill W6WRT
>>>
>>
>> "It all depends" as they say.
>>
>> Some ceramic/metal and glass/metal are notorious leakers such as the 
>> 4CX300A and PL-172 and PL-172A. Popular ones such as the 4CX150A 
>> family, 8874 family, 8877, 3CX3000A, 4CX1000A/1500B hold vacuum well 
>> but the indirect heated types such as the ones above (not the 3X3) 
>> should be run up to 24 hours with just filaments to regetter from 
>> outgassing. This includes the 8072/8121/8122 and long stored Russian.
>>
>> Eimac had a couple of  bad years in the late 80's with the 3-500Z when 
>> they moved the plant to SLC; other than that they just had outgassing 
>> as did most glass tube and need regular running with color to regetter.
>>
>> The 3-1000Z and 4-1000A often went to air as well as did many of the 
>> larger WW2 tubes such as 450/750 TH/TL, 6C21, and larger.
>>
>> OTOH I have a pair of 1934-35 HK-354's that still run at a KW on AM 
>> but other 20's to 30's TX tubes are almost impossible to find (mostly 
>> RCA) with seals intact; 203A, 204A, 211, 849, 851, 852, and others.
>>
>> Ive little to no experience with Russian and non US clone Chinese 
>> tubes but have heard a lot of good things about Chinese 
>> military/broadcasting ones in particular.
>>
>> Carl
>> KM1H
>>
>>
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>>
> 
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