[AMRadio] Tube Plate Dissipation Ratings


Jim Candela jcandela at prodigy.net
Thu Oct 7 14:31:41 EDT 2004


Tom,

   The link below has the data sheet for your tube.
Notice that the link has carriage returned, so you
must manually type in the rest of the URL.

   Tubes like yours are designed to run hot, and red.
The manufacturer comes out and says that while
boasting excellent vacuum even if the tube is
overloaded.

   Newer tubes like a 6146, and especially sweep tubes
need more pampering. These dudes if overloaded
significantly will never be the same again. This
happened on my QRO 20A where I accidentally shorted
out the bias on a EL-34, and the tube superheated
about 15 seconds until the fuse popped. That did the
tube in; it's shot! It still works, but pretty flat on
emission now.

    Also consider a tube that is rated at 25 watts
with convection cooling will be capable of more with
forced air cooling. The main concern is that the glass
to metal seals don't get too hot. Forced air won't
help much if the internal elements get so hot that
they emit gas such that the vacuum is compromised.

   I remember hearing of folks using WW2 1625's upside
down in oil to allow pushing the tube harder, and
longer. Hey when they could be had for 25 cents each
in quantity, why not?  

Here is the 2 line link:


http://www.mif.pg.gda.pl/homepages/frank/sheets/114/h/HK24.pdf

Regards,
Jim

--- Tom Elmore <tom at telmore.com> wrote:

>      Can someone please clarify for me the plate
> dissipation ratings on
> vacuum tubes.  I am in the process of restoring a
> Stancor 60N  that uses a
> HK24 tube and the dissipation rating is about 25
> watts.  Isn't the 25 watt
> rating  Ep*Ip and is this a maximum value that
> should never be exceeded?  I
> believe this transmitter will put out 30 to 40 watts
> of carrier and if it
> were say 60 efficient wouldn't that bump up the
> plate dissipation to around
> 65 watts exceeding the dissipation ratings.
> 
> 
> Thank You
> Tom Elmore  KA1NVZ
> Anchorage  Alaska
> 
>
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