[AMPS] AL811H saga continues

[Tom Rauch]

<italic><color><param>0000,0000,0000</param>> I got the new Svetlana 811a tubes from RES in today and dropped 

> them in tonite, but still can't get full power out of the amplifier. I can

> load the amp up with up to 200ma grid current, 450 ma plate current and

> 1500v high voltage, but the most I can get out of it is 500 watts cw.  


</italic></color>Typical CW rating is 600 watts. You aren't that far off. Could be 
your wattmeter is wrong that amount. What kind of wattmeter do 
you have?


The plate current sounds low. The continuous current rating of the 
tubes is 175 mA per tube, for a total of 700 mA. You can run up to 
that amount of current on CW, and more than that for brief periods 
of tuning. 

 


<italic><color><param>0000,0000,0000</param>> I originally thought that maybe because of the plate to grid short in the

> original tube that maybe there was something wrong still in the driving

> section on the tubes, ie a bad cap or something, so I pulled out 2 tubes

> and could still get the same amount of power out of the amp, so then I

> pulled 2 diagonal tubes out and did the same test and got the same

> results.  


</italic></color>Cathode driven tubes in parallel don't add much gain. That sounds 
completely normal. If you run 600 watts out with two tubes, you'll 
cook the tubes however.

<italic><color><param>0000,0000,0000</param> 

> So this rules out that there is still a problem with grid 

> resistors/series blocking caps etc. Going from 2 to 4 tubes only 

> changes the output by 5-10 watts, and doesn't change the 

> plate/load tuning much at all either. 


</italic></color>Just as it should. 

<italic><color><param>0000,0000,0000</param> 

> Help! Anyone got any ideas besides send it back to Ameritron? 


</italic></color>Apply more drive, run more plate current. Don't stop at step 8 in the 
tuning instructions, continue to step 9 where you increase drive. 
Read the note, where it says to never exceed 750 mA plate current 
while tuning.


Sounds like everything is normal so far.  

<nofill>
73, Tom W8JI
w8ji@contesting.com

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