[Collins] KWM-2A output

[Robert & Linda McGraw K4TAX]

An alternative approach, with the unit off, using a DVM measure the total 
resistance from one of the cathode pins to ground.  Then with the tubes 
drawing current measure the voltage from a cathode pin to ground.  I = E/R 
will then tell the current based on the accuracy of your measurements.  The 
accuracy of low values of R can be difficult to determine due to meter lead 
resistance, contact resistance and etc.  If you are able to determine these 
then subtract the values from your measurement.

In the case of my 32S-1, there is a series resistor (825 ohms) between the 
cathode circuit and the meter switch.  This value may have migrated up thus 
introducing a meter error, but in the opposite direction.  {Meter indicates 
less than actual current.} Also, the 6 resistors between the cathodes and 
ground are 12 ohms each for a total value of 2.0 ohms.  Thus 250 ma of 
current produces 0.5 volts.

Performance wise: output power is 110 watts, input power is 177.5 watts for 
an efficiency of some 62%.  E = measured 710 VDC, I = 0.250A  {Current 
values do include screen current of some unknown value.}

73
Bob, K4TAX


----- Original Message ----- 
From: "Glen Zook" <gzook at yahoo.com>
To: <wabate at dandy.net>
Cc: "Collins CRA" <collins at mailman.qth.net>
Sent: Saturday, March 12, 2005 9:53 AM
Subject: Re: [Collins] KWM-2A output


> There are 6 resistors, not just one.  They are in
> parallel and thus reduce the shunt value to 1.66667
> ohms.  The 6146 has a total of 3 pins that are
> connected to the cathode and there is a 10 ohm
> resistor from each of these pins to ground.  Two tubes
> makes for a total of 6 resistors.
>
> Glen, K9STH
>
>
> --- Bill Abate <wabate at dandy.net> wrote:
>
> But the comments on the cathode resistor did resonate
> with me.  I also forgot about cathode current vs.
> plate current.  You gave me enough to suspect so I
> think I will pull the 2A and check the resistor by
> inducing a known current in it.
>
> Glen, K9STH
>
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