On Mar 29, 2005, at 7:34 AM, TexasRF@aol.com wrote:
>
> In a message dated 3/28/2005 10:54:45 P.M. Central Standard Time,
> W4EF@dellroy.com writes:
>
> Good point, Gerald. A more likely explanation for the low efficiency
> on 10 meters might be a combination of higher tank circuit losses
> and wattmeter calibration error.
>
> Still, I hear people talking about "soft" tubes a lot. I can
> understand
> broadcast pulls have low filament emission, but aside from that
> are there any other mechanisms which will result in diminished
> output capacity from a tube like the 8874?
Since gold poisons electron emission, 8874s that have gold meltballs
stuck to the cathode's emissive coating exhibit lesser emission.
Fortunately, gold meltballs can be dislodged by tapping vertically on
top of the anode cap with the flat side of a small ball-peen hammer.
However, the tube should be kept base down at all times thereafter to
prevent the loose meltballs from getting on the anode-grid insulator
and causing a HV-chassis gnd flashover.
cheerz, Mike
>
> Mike,
> W4EF...................................................................
> .....
> .
>
> ----- Original Message -----
> From: <TexasRF@aol.com>
>>
>>
>>
>> And this brings up the question: Why would a soft tube show up on 10m
>> operation and not lower frequencies?
>>
>> 73,
>> k5gw
>
>
>
>
>
>
> Hi Mike,
> I didn't intend to question the validity of soft tubes showing first at
> higher frequencies. I have always been under the impression that this
> is true but
> just now wondering why it might be true or even if it is true.
>
> 73,
> Gerald/k5gw
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>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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