[Hammarlund] : Tube shields and heat

[manualman at juno.com]

I have tube receivers here that have been running for 50 years with their
silver shields in place. Never had a crap-out due to heat-related tube
stress. I would suspect if you really want to reduce tube heat stress,
drop your filament voltage down by 10% or drop the input line voltage to
110 or 105 volts.

I also recall back in the "good old days" of doing a receiver alignment
with all the tube shield off. Of course after completing the alignment, I
realized the shields were off so I put them back in place. For fun and
giggles I rechecked the oscillator and IF alignments and found all the
adjustments had to be touched up to some degree.

Personally, I'll side with the original designers; they had tube shields
on certain tubes for whatever reason, so my shields will stay in place as
they came from the factory. I'm probably not smarter then they were.

Pete, wa2cwa

On Sat, 27 Sep 2014 15:19:55 -0700 "Kenneth G. Gordon"
<kgordon2006 at frontier.com> writes:
> On 27 Sep 2014 at 17:24, Bill wrote:
> 
> > All this redesign of tube shields, make me wonder why the 
> engineers that
> > designed them didn't think of some of these tips...OR they 
> designed them to
> > work in the way they do. Bill W2CQ
> 
> I suspect that the reasons are several: first of all, I still 
> believe the shields 
> were added to prevent radiation, RF, either from an external source 
> (a big 
> transmitter in the same room) from effecting certain circuits in the 
> receiver, or 
> to prevent RF-radiation from certain circuits in the receiver from 
> causing 
> other outside effects.  
> 
> The heat problem was not considered, or if it was, it was considered 
> to be 
> minor, especially in a military situation in which (supposedly) 
> maintenance 
> was ongoing and organized, and tubes were bought by the millions.  
> 
> Secondly, much of the information and data on the effects of heat in 
> tubes 
> and how it shortens their lives came about AFTER the earlier types 
> of 
> shields were designed and implemented.  
> 
> As soon as the heat issues became better known, the military had 
> heat-reducing shields manufactured and used: i.e., the so-called 
> IERC tube
> shields.
> 
> After all, there is a pretty constant improvement in knowledge and 
> understanding of many things. Heat in tubes is probably one of 
> those.
> 
> We come along much later and need some way to reduce the heat in 
> tubes, 
> thus increasing their life expectancy, since those tubes are 
> becoming more
> difficult to find, since many haven't been made in many years.
> 
> And, most of us cannot find, or if we do happen to find, cannot 
> afford, IERC
> tube shields.
> 
> Therefore, we do what we can to at least mitigate the problem.
> 
> I believe it was Eimac who first did some extensive testing of 
> tube-life versus
> heat (and filament voltage) and published their findings long after 
> the earlier
> tube shields were designed....which were designed for the sole 
> purpose of
> cutting down on radiation, RF, effects.
> 
> Anyway, that's the way I see it, and it is worth exactly what you 
> paid for it.
> 
> Ken W7EKB
> ______________________________________________________________
> Hammarlund mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Hammarlund at mailman.qth.net
> 
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
> 
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>