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Hickok TV-7/U Low readings

pixelriffic

pixelriffic

New Member
Just bought this tester from Ebay. It was sold as serviced and calibrated. I was tested a number of known good 6CA7s, and it consistently showed about 5 ticks below the value in the guide. Worth noting that these tubes have been checked by two other testers. Small signal tubes, 12AX7s for example, behave as expected. For the power tubes, I have discovered that if I use the line adjust with the tube instated, I then get the expected reading. What makes me a bit crazy, is that I let go of a 539C a couple of years ago that behaved exactly the same way. No claims of calibration or service were made on that one. And yes I know, line adjust is intended to be done without a tube installed.

My dilemma is whether or not I should return the unit. Thoughts are appreciated.
 
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pixelriffic said:
Just bought this tester from Ebay. It was sold as serviced and calibrated. I was tested a number of known good 6CA7s, and it consistently showed about 5 ticks below the value in the guide. Worth noting that these tubes have been checked by two other testers. Small signal tubes, 12AX7s for example, behave as expected. For the power tubes, I have discovered that if I use the line adjust with the tube instated, I then get the expected reading. What makes me a bit crazy, is that I let go of a 539C a couple of years ago that behaved exactly the same way. No claims of calibration or service were made on that one. And yes I know, line adjust is intended to be done without a tube installed.

My dilemma is whether or not I should return the unit. Thoughts are appreciated.
Click to expand...
According to the manual, page 17, paragraph (9), line adjust is done after the tube under test is inserted, paragraph (7) on page 16.
 
ramjet said:
line adjust is done after the tube under test is inserted
Click to expand...
^^^This! My Hickok 6000 is the same. I believe it's because the filament current drags down system voltages. Small signal tubes like the 12AX7 draw very little current, so they don't behave this way.

Jack
 
I'm not an expert on the TV-7 or tube testing in general, but looking at Page 1 of the Department of the Army technical bulletin TB 11-6625-274-12/1.
1. Operation
a. Turn the POWER to the ON position.
b. Press push button 1-LINE ADJ and hold it down. (etc. and adjust it)
Then
c. Locate the type number of the tube to be tested
and set the filament voltage and bias and other knobs (I think of it as a telephone number) push the right test button

I've never heard of setting the line adjust for each tube.

And of course, you have to keep in mind that the TV-7 was military and the guys had different jobs than matching EL-34s for stereo amps.
 
I've always adjusted the line voltage on my Hickok 533 with the tube installed. It only makes sense. As Jack says, the filament current will drag down the test voltages. I think the OP's tester is fine.
 
You might test for the tube filament voltage in one of the other sockets to see if the line adjust is in fact bringing the voltage up to what it should be. For example, testing a 6BA6 and then maybe a 5U4. They consume vast different current for the filament. If you adjust the line adjust for the correct voltage when the tube is in the socket, it may not be at full voltage.
 
ramjet said:
According to the manual, page 17, paragraph (9), line adjust is done after the tube under test is inserted, paragraph (7) on page 16.
Click to expand...

Well holy cow! You are correct! I think what threw me, and more than a few others it seems, is that setting line voltage is also mentioned earlier in the manual before the tube is inserted. Apparently they just wanted to get it in the ballpark, and then dial in based on current draw. Really nice example of this tester. Sure did not want to let this one go.

Thanks so much!
 
pixelriffic said:
Well holy cow! You are correct! I think what threw me, and more than a few others it seems, is that setting line voltage is also mentioned earlier in the manual before the tube is inserted. Apparently they just wanted to get it in the ballpark, and then dial in based on current draw. Really nice example of this tester. Sure did not want to let this one go.

Thanks so much!
Click to expand...
And that is probably good enough so that you don't have to check the actual voltage at the socket! "Problem" solved!
 
BTW, the Heathkit TT-1A that I have instructs you to do the same, insert the tube, move the lever from "Disconnect" to "Normal" and then adjust the line. Good on 'ya!
 
Jalousie said:
I'm not an expert on the TV-7 or tube testing in general, but looking at Page 1 of the Department of the Army technical bulletin TB 11-6625-274-12/1.
1. Operation
a. Turn the POWER to the ON position.
b. Press push button 1-LINE ADJ and hold it down. (etc. and adjust it)
Then
c. Locate the type number of the tube to be tested
and set the filament voltage and bias and other knobs (I think of it as a telephone number) push the right test button

I've never heard of setting the line adjust for each tube.

And of course, you have to keep in mind that the TV-7 was military and the guys had different jobs than matching EL-34s for stereo amps.
Click to expand...
From the publication you referenced:

j. Insert the tube ~ be tested in the proper socket.
k. Readjust the line voltage (b above).
 
Jalousie said:
I'm not an expert on the TV-7 or tube testing in general, but looking at Page 1 of the Department of the Army technical bulletin TB 11-6625-274-12/1.
1. Operation
a. Turn the POWER to the ON position.
b. Press push button 1-LINE ADJ and hold it down. (etc. and adjust it)
Then
c. Locate the type number of the tube to be tested
and set the filament voltage and bias and other knobs (I think of it as a telephone number) push the right test button

I've never heard of setting the line adjust for each tube.

And of course, you have to keep in mind that the TV-7 was military and the guys had different jobs than matching EL-34s for stereo amps.
Click to expand...

I had not heard of it either, until this post. I was first shown how to use a Hickok by an old timer, as I suspect more than a few out there have. BTW, I also see the same thing in the 6000A manual. Nothing to do with the TV-7 being more basic. It's mainly so in the simplified meter. I wondered why two other and different Hickok's exhibited exactly the same behavior. I just happened to notice that adjusting line voltage seemed to deliver expected results.

After now having tested quite a few tubes with the correct procedure. I'm getting the results that make sense now. It works just as designed. And by the way, here is a pretty slick calculator to get the actual mmho numbers: https://tubesound.com/tv-7-micromhos-conversion-calculator/
 
Last edited:
Came looking for causes for the 750 I'm working on to have low readings on certain tubes. I did not know this either! Soon as I can get back in the shop I'm going to try this.
 
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