[JMS] power supply success

[Don Buska]

Hi Ronnie,

Per the spec sheet in Plate-Modulated RF PA (Class C) operation 
(See http://www.qsl.net/n2ckh/6146.pdf) with a plate voltage between
480 and 600 VDC the screen voltage should be 250VDC max.  Normally in the
Millen transmitter the screen voltage is derived through a 4.7K 1W resistor 
from the LV supply (mine is set for +250VDC).  This is for CW operation.  During AM it 
is via a voltage divider off the HV supply (They modulate both plate and screen).

With your 81 volt drop across the screen resistor it sounds like you have way to much 
screen current.  With a 250VDC screen voltage there should be around 50VDC drop across 
the 4.7K screen resistor assuming about 10mA of screen current.  

Question are your conditions measured under transmitter operation, i.e. oscillator is 
running and you are properly loaded into the antenna?  What grid bias are you using on 
the 6146?  Should be around -65VDC.  Be careful with such a large screen current.  
You'll distroy the tube, plus you will exceed the screen resistor power rating also.  
What does the 90801 meter indicate for screen current?  Manual states not to exceed 
15mA.

73

Don N9OO



On Thu, 08 Jan 2004 08:33:38 -0500, w5sum wrote:

>well I have completed the power supply for me 90801. It only delivers about
>450 volts under load on the B+, and I am taking the screen voltage off of a 
>25K 100 watt tapped resisitor that is the bleeder in the power supply. I 
>powered her up this morning with a variac on the power supply. After perhaps 
>an hour of burn in, I had the power supply at full line voltage and the 
>little rig sat there fine, with no smoke and no bad smells LOL
>
>WHAT is the proper screen voltage? I have about 100 volts going to the rig 
>and on the other side of the screen dropping resistor there is 19 volts. 
>
>Does all of this sound in line?
>
>If I get a positive response to that question, I'll power her up tonight and 
>put her on the air on cw
>
>thanks for the help y'all
>
>Ronnie
>
>The "AM" voice of Shreveport, Louisiana USA
>formerly WN5AIA and WB5AIA
>I got my Extra Class the old fashioned way... I earned it!
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