[Amps] Holding a vacuum

[Carl]

----- 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