[Collins] 6146 testing in KWM-2

[Dr. Gerald N. Johnson]

In the latest Collins Journal, there is a suggestion to pull the plate
connection of one 6146 at a time to compare the tube currents for
matching. That is a BAD idea because it doesn't isolate tube current and
its abusive to the tube with the plate cap disconnected.

When a pentode or tetrode is operated without plate voltage, the current
that would have been drawn by the plate is drawn by the screen which
doesn't have the power dissipation capacity. The cathode current may
remain the same and the screen may well glow red. That's not its normal
operating condition and isn't healthy for the screen. So the current
reading is from both tubes, not a true indication of balance. Then
reading 20 milliamps on a 300 milliamp full scale meter is fraught with
large errors from pivot friction.

Don't do it.


-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer