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Re: Resetting the line adjust on a Hickok with Plate Current Flowing

Posted by Steve O (A) on September 4, 2003 at 21:26:01

In Reply to: Resetting the line adjust on a Hickok with Plate Current Flowing posted by Chris Haedt on September 4, 2003 at 05:07:28:

Here’s my take on the voltage thing based on a TV-7B/U.

Background (but you probably already know this): The PT for the TV7 has a 93VAC primary with a 200ohm rheostat in series for voltage adj. The DUT filament secondary is tapped from 0.6VAC up to 117VAC. When the line adj button is pushed it connects the indicating meter as an AC voltmeter across the 0-117VAC secondary. The unit had been recently checked and calibrated per the instruction manual that came with it. I measured the voltage at the primary of the PT, the voltage at the 117 VAC winding (which drives the meter in line adj mode) and filament voltage at the tube socket. Everything was set up for a 6L6.

Findings:

Tester State.................................Pri voltage...Voltage at 117 tap...Voltage at socket...gm indicator
Idle......................................................90................116.........................6.4
6L6 no line adj, no plate cur..................86...............110.........................5.7
6L6 w/line adj to mark, no plate cur.......91..............117.........................6.1
6L6 w/line adj as above, S3 pushed.......86..............109.........................5.7..................40/25
6L6 w/line readj to mark, S3 pushed......91..............116.........................6.1..................44/25

Pushing the “test” button while the “line adj” button was pushed w/o tube did not affect line reading.

I conclude from these meas that on the TV7 at least, setting the line adj in any mode will set PT secondary voltages to the same value regardless of load so one IS reading the right thing...addl meters not needed. Apparently the TV7 is different from the 533 you checked. Seems that other Hickok testers like 752 and 800 also operate the same way with line sense point taken at the secondary of the PT. Also, although the actual condition of the 6L6 was unknown, the readings are plausible and the value increased “only” 10% by readjusting line voltage. Still doesn’t unequivocally answer the question of whether or not it’s acceptable to readjust although the case continues to build that it’s not.

BTW do you have chart info for 752A that includes later tubes like 6KD6 , 6JK6 and so on.

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