[ARC5] Glass or Metal Tubes Preferred for Receivers?

[jeepp]

In the Signal Corps history series and in an ad I recall in an early 1940s QST, the point of ruggedness and "reliability" was mentioned.  That would seem the point.  Were there a marked difference, I'd think someone would have shined a light, by now.  Regarding actual use, my experiences mirror Bill's.  No factor....Jeep K3HVG


Sent from my Verizon 4G LTE smartphone

-------- Original message --------
From: Bill Cromwell <wrcromwell at gmail.com> 
Date: 2/4/18  23:11  (GMT-05:00) 
To: arc5 at mailman.qth.net 
Subject: Re: [ARC5] Glass or Metal Tubes Preferred for Receivers? 

Hi Mac,

I remember seeing something about the metal tubes running hotter which 
might shorten their lifespan. I believe the metal shell is or can be 
grounded at one of the pins for better shielding/isolation. I have even 
heard of hams inverting the metal tubes amd immersing the metal shells 
in water or mineral oil to try and get more power out of them. I don't 
know how successful that was or how we measure success. How much did 
they get back for all the effort.

Glass tubes might cost a little less. As for shielding/isolation - how 
much is needed in a given application? An entire stage, tube and all, 
could mounted in a shield enclosure that could be more effective than 
shielding just the tube.

I have samples of some tubes in both glass and metal that were pulled 
from service. Some of them I know had been in use until shortly before I 
acquired them. There didn't seem to be much difference in lifespan - all 
of them are vigorously healthy. I do admit to not knowing their 
birthdates nor how much overtime any of them may have been on the job. 
But they had been in use and are as old as me or older.

I have put glass tubes where metal tubes used to be and vice verse. I 
didn't notice any difference but I don't have much in the way of 
laboratory measuring instruments. So there is my best guess. Run 
whatever you have. Especially if you are not taking your radio up to 
25,000 feet in a unpressurized, piston engined bomber. <shudder>

73,

Bill  KU8H



On 02/04/2018 08:55 PM, D C _Mac_ Macdonald wrote:
> Is there a performance and/or lifespan difference between the tubes?
> I.E., 12SK7 or 12SK7GT preferred?
>
>
> 73 de Mac, K2GKK/5
> (Since 30 Nov '53)
> Oklahoma City, OK
> USAF Retired 61-81
> FAA Retired 94-10
>
>
>
>
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-- 
bark less - wag more
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