|[AMRadio] Current on 6146s|
John E. Coleman (ARS WA5BXO)
wa5bxo2006 at pctechref.com
Sat Feb 10 11:52:33 EST 2007
I have found it to be very important to make measurements while in
operation. Except that RF will mess up the meter readings. This is why I
said to ground the grid directly and then kick the rig to XMIT and make the
measurements then. Checking the plate voltage on the plate while the tube
is cut off is not conclusive as there may be a high resistance between the
plate point and the power supply point (all the way back in the power supply
circuit) and same could be true of the screen. This would cause the plate
voltage to appear normal until you draw current then it may drop real low at
the plate point but still be good at the power supply. RF at the plate will
cause the meter to read wrong and grounding the grid will kill the bias and
RF. If the rig were operating normal then grounding the grid would cause
excessive plate current so this is a good check any way.
1. While in XMIT mode, when you ground the grid, the plate current should go
above 200 ma. If it does, then troubleshoot the grid circuit.
2. If it does not, then leave the ground on the grid and stay in XMIT mode.
Then measure the plate and screen voltages. One of them is surely wrong.
The only other possibility would be the filaments are not lit up good.
Rule for the day:
You can't have a 100 volt drop across a good 5ft #12 wire with out a fire.
John E. Coleman (ARS WA5BXO) wrote:
> What you're saying is that at no time, can you get more that 20 ma of
> plate current? Try grounding the control grid and see if the finals
> draw current then. If not be sure to check the screen voltage and
> plate voltage while the grid is grounded. And check these directly on
> the plate and screen connection.
Of course, that was -not- supposed to go to the whole list.
No worries though... 5 landers? 3.880 in the morning, if you're not
interested in the Traders net on 3.890?
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