[Amps] Holding a vacuum

[Pete N4KW]

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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