[AMPS] Q: Eimac 290A

[2]

>Looking for tech.specifcations on the 290A Eimac tube
>I would expect that data can be similar as for the nCX5000 types
>It sits in a SK-291A socket.
>
//  The 290 is a Class AB1 pentode with an oxide-cathode and a delicate 
2w grid.   The heater needs 17A at 5.7 - 6.3 volts. Anode ratings for AŘ 
are 6000V, 2A.  For SSB, 7000V should be ok.  To get 2a, the 
screen-potential needs to be c. 900v.  Since the 290's screen is subject 
to reverse-current, a zener string shunt regulator would be good.  Zener 
current needs to be c. 65mA.  To protect the delicate screen from 
over-current, the zener string should fed from a power resistor connected 
to a 3000v or more source.   I would use a string of 24v - 30v, 5w zeners 
mounted on perforated board, near the cooling airflow. [note - "5w-rated" 
zeners should not be operated above 2w without liquid cooling].  With a 
150w transceiver, the needed 120V-peak RF grid voltage can be achieved 
with a 50-ohm grid termination.  My guess is that 9k-out PEP should be 
possible on SSB.  Back off the mic. gain until the anode-I doesn't 
modulate (a.k.a. Class A) and you should have around 1k out.  .  .    
"Speak softly and carry a big stick." 

cheers, Chris

-  R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.  
end


--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com