[Johnson] Ranger Question

[Roy Morgan]

On Apr 17, 2009, at 11:33 AM, Michael Hardie wrote:

> ... There are two "oddities", the drive control is about
> 1.5 on it's dial and the grid current reads 0.4 ma when the plate  
> current
> reads 140 ma, the manual states that the grid current should be  
> around 2.5
> ma.

The final may be oscillating.  Check with a scope on the output and a  
string of dits from a keyer or bug.  The keyed waveform may show  
oddities if it it oscillating.

Check the grid metering system with all power off and a known  
(negative) current injected into the final grid(s).  The meter should  
indicate more or less what the injected current is.  Valilant (and may  
be Ranger) meter shunts are bits of wire that don't LOOK like they are  
anything but a loop of wire.


>  And the 6146 screen voltage (Again with 140 ma plate current) is 160
> volts, not 190 volts as per the manual.

Power out put will vary considerably with screen voltage/current.  The  
screens act as a big throttle on the tubes' power handling.

> The coupling controls have very
> little effect, indicated power on an accurate wattmeter/dummy load  
> is a
> couple of watts.

Seems like the final is not amplifying.  What's the final grid voltage/ 
bias?  Are all caps in the drive circuit working ok?  Is some bypass  
cap open (like the one at the cold end of the driver plate circuit  
C-36?)?  A disk ceramic with clips on its leads can tell you a lot  
here.   Hook in parallel with any bypass cap you have, such as at  
screens or driver plate tank cold end.

We assume you've swapped out the final tube.  Then the driver tube.

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073