[Hammarlund] : Tube shields and heat

[Guido Santacana]

Lowering line input voltage readily works. I have all of my older tube gear
running on 110VAC. Heat output was reduced and I noticed it more on my SX28
audio output tubes.

73s

Guido Santacana KP4FAR

On Saturday, September 27, 2014, manualman at juno.com <manualman at juno.com>
wrote:

> 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 <javascript:;>> 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
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