[Hammarlund] purpose of tube shields

[Todd, KA1KAQ]

On Fri, Sep 26, 2014 at 12:16 PM, Les Locklear <leslocklear at hotmail.com>
wrote:

> Removing the tube shields completely cools even better. I have IERC
> shields on a couple of receivers,
> the others have none. Unless you are transmitting close by and don't want
> to spring for the pricey IERC shields, simply remove them.
>

Les is right - removing the shields except in 'shield-critical'
applications is the best bang for the buck, for sure. And as Pete says, in
sporadic amateur use it's not an issue anyway. Even line voltage shouldn't
be a problem when you consider the +/- spec built into most gear. Though
reducing higher line voltage is a good thing, especially considering old
components like transformers.

As others have stated, more often than not in later gear (particularly
military), the locking shields were used more to keep tubes in place. In
early radio gear proper shielding was a much bigger issue than decades
later.

The late Bill Kleronomos/KD0HG did a pretty extensive review of heat
dissipation for tubes with and without shields of different types. IIRC, it
was published in Electric Radio Oct '94 and shows that the IERC shields
actually work better than a bare bulb. No doubt due to their heatsink
design. No other tube shields do. He tested all types, including the Elco
and Collins types as I recall along with shiny and black painted. My
recollection is that painting them black is only a slight improvement over
a bare shield.

We need to keep in mind that tubes were cheap and plentiful then,
everything used them. So if their life expectancy was cut by 25% or more,
so what? Swapping out tubes before failure as part of a PM plan was
commonplace. Many a ham has benefited from broadcast transmitter pulls.

If you look around online you can likely find Bill's article and the
columns of data are clear.


~ Todd,  KA1KAQ/4