[Amps] Soft Tubes?

[Richard Measures]

On Mar 29, 2005, at 7:34 AM, TexasRF at aol.com wrote:

>
> In a message dated 3/28/2005 10:54:45 P.M. Central Standard Time,
> W4EF at 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 at 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