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OK--I had to try this. I had a 533 on the bench and set it up with an external meter monitoring the primary of the power transformer--so that I could tell what was happening.First I tried pushing the P4 test button at the same time as the line adjust button. This caused the meter to deflect downward about a 1/4" but did not affect the reading on the external meter monitoring the primary of the tube tester's transformer--it stayed at about 95 VAC when set to line the normal way.
Next--I placed a 6L6 in the tester and tested it the normal way. The primary of the transformer was 95 volts when set to line, and the tube tested at 5200--which is right on the money.
Now I tried the line reset method. When I reset the line with the P4 test button depressed, the primary of the power transformer went up to 105 volts. With the line adjust set this way, the tube tested at 7000--which is WAY off the mark. It sure would make those weak tubes look better by testing them this way!
So based upon my 533 test (and this may not be the same for all Hickoks--but I'll bet it is):
(a) when you press both buttons at once you are not really setting the primary of the power transformer properly. And we KNOW the Hickok method for this was to add a meter at the transformer primary as in the 539C.
(b) when you reset the line with both buttons at once, the reading you obtain will be grossly high. A 6L6 went up nearly 2000 micromhos this way. It is obvious that a 6L6 should NOT read 7000 on a 533, as the nominal value printed on the chart is 5000.
So--best use the tester as designed. I have to admit that I had not tried pressing the P4 and Line adjust at the same time, and you do get a reading on the meter. Problem is you are obviously not reading the right thing, and need to add additional meters to do this line reset thing--just like they did on the 539.
Follow Ups:
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..................44/25Pushing 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.
I do have 752A data that shows those tubes. I got the data from SND Tubes, owned by Mike Marx. Mike does an excellent job with manuals and I recommend him highly. He has an extensive knowledge of tube testers and has a great stock of NOS tubes. Visit his web site to see all the manuals and data--plus all the tubes.
I tried testing a 6L6 on a TV10, and it behaved much as your TV7 did--the value went up about 10% with the reset. The line adjust circuit is different on these military testers from civilian Hickoks--they have separate instrument rectifiers that drive the meter during the line adjust test. The civilian testers take rectified DC from one of the tester's tubes to drive the meter during the line adjust test.Still, the instructions for the TV10 are pretty clear about setting the line when you turn on the tester and again when you put the tube in to test it. The next step is to press the appropriate test button. There is nothing about resetting the line with the Gm test button depressed at the same time. Even though this CAN be done, the roll chart data is not based upon the tester being operated that way--and if it were--the instuctions for the TV7 and TV10 would have called out the step you described. So--if you don't operate the tester as outlined in the manual, the reject points in the manual would no longer be valid. These reject points would have to be adjusted upward based upon the plate current of the tube under test. There are two more factors to consider. First--it may be that resetting the line with the Gm button depressed COULD damage the tester with certain types of tubes--or with certain types of tube shorts--this I don't know. Second--on testers like the 539 (where the AC line is reset with plate current flowing), the bias must be reset also--something that would require an additional meter.
While I must agree that your reset method does seem to bring the voltages closer to what WE think they should be--this is clearly NOT the way the military intended the testers to be used. We don't know all the reasons why the procedure was written as it was, and my advice is still to operate these testers per the manual. The people that designed all this stuff were pretty clever, and trying to "second guess" their operating procedures is probably not a prudent course to follow.
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