In testing a 6Q7G tube I get a good reading until I wave my hand over the grid cap. Then the reading falls to almost dead. Never noticed this before and wondering if this is and indication of tube problem or what? This tube tests ok with no shorts.
As you can tell I am fairly new to testing.
The tester is a GE TC3 / Emmision Type.

:In testing a 6Q7G tube I get a good reading until I wave my hand over the grid cap. Then the reading falls to almost dead. Never noticed this before and wondering if this is and indication of tube problem or what? This tube tests ok with no shorts.
:As you can tell I am fairly new to testing.
:The tester is a GE TC3 / Emmision Type.
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If you're testing a tube with and external grid, why don't you have a clip lead on the grid cap? And if you don't have a contact on the tube grid, how do you know the tube is good?
As far as waving your hand over the tube, sounds like the grid, which is VERY sensitive, is picking up a stray capacitance.
Anybody else have any ideas?
Terry

Terry/Scott,
With the grid cap terminated correctly at the tube tester, don't see how hand/body capacitance would affect the reading. On the other hand if grid cap is not connected properly to the tester, it's anybody's guess as to the results.

marv

::In testing a 6Q7G tube I get a good reading until I wave my hand over the grid cap. Then the reading falls to almost dead. Never noticed this before and wondering if this is and indication of tube problem or what? This tube tests ok with no shorts.
::As you can tell I am fairly new to testing.
::The tester is a GE TC3 / Emmision Type.
::
::
::
::
:
:Okay Scott, I'm confused.
:If you're testing a tube with and external grid, why don't you have a clip lead on the grid cap? And if you don't have a contact on the tube grid, how do you know the tube is good?
:As far as waving your hand over the tube, sounds like the grid, which is VERY sensitive, is picking up a stray capacitance.
:Anybody else have any ideas?
:Terry
:

Sorry for the confusion...The grid cap lead is indeed attached from the tester to the tube. I have never noticed this with any other tubes and that is what got my attention. I will check the lead for short but I am not touching the lead when the tube reads good and when my hand waves over top the tube.....goes directly to bad??

Scott, I don't have a schematic for TC3 but on emission testers usually all elenments grounded except plate. Waas the grid cap lead attached to grid cap? If so it should be grounded with other elements and your hand near it should have no effect. Possibly the grid cap switch/wire open? Does it happen only on that tube (6Q7)? zIf so that position on grid cap may not be closing. PL

:In testing a 6Q7G tube I get a good reading until I wave my hand over the grid cap. Then the reading falls to almost dead. Never noticed this before and wondering if this is and indication of tube problem or what? This tube tests ok with no shorts.
:As you can tell I am fairly new to testing.
:The tester is a GE TC3 / Emmision Type.
:
:
:
:

Well I went down to check the tube this morning and changed one thing. Yesterday I had the tube tester plugged into the variac because it was close. Today I plugged directly into 120 outlet and the tube tested ok with no change with hand over grid cap. Don't know why the difference but that is the end of this issue. Just won't plug in variac again.

Must have something to do with Mr. Ground.
:Well I went down to check the tube this morning and changed one thing. Yesterday I had the tube tester plugged into the variac because it was close. Today I plugged directly into 120 outlet and the tube tested ok with no change with hand over grid cap. Don't know why the difference but that is the end of this issue. Just won't plug in variac again.
:

:Must have something to do with Mr. Ground.

Or Gremlins.
Order my patented Gremlin remover for only $19.95. Order in the next 5 minutes and get two PLUS a pair of Ginsu knives These are guaranteed to cut through the magic "smoking" phenomenon so prevalent in antique radio repair.

Ha ha-
Terry
(non compos mentis)
::Well I went down to check the tube this morning and changed one thing. Yesterday I had the tube tester plugged into the variac because it was close. Today I plugged directly into 120 outlet and the tube tested ok with no change with hand over grid cap. Don't know why the difference but that is the end of this issue. Just won't plug in variac again.
::
:

Very funny,Terry. Will you throw in a free chamois with the order????
Andy

::Must have something to do with Mr. Ground.
:
:Or Gremlins.
:Order my patented Gremlin remover for only $19.95. Order in the next 5 minutes and get two PLUS a pair of Ginsu knives These are guaranteed to cut through the magic "smoking" phenomenon so prevalent in antique radio repair.
:
:Ha ha-
:Terry
:(non compos mentis)
:::Well I went down to check the tube this morning and changed one thing. Yesterday I had the tube tester plugged into the variac because it was close. Today I plugged directly into 120 outlet and the tube tested ok with no change with hand over grid cap. Don't know why the difference but that is the end of this issue. Just won't plug in variac again.
:::
::
:

:Very funny,Terry. Will you throw in a free chamois with the order????
: Andy

Only if you order the "How I survived eBay DVD".
T.
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:
:::Must have something to do with Mr. Ground.
::
::Or Gremlins.
::Order my patented Gremlin remover for only $19.95. Order in the next 5 minutes and get two PLUS a pair of Ginsu knives These are guaranteed to cut through the magic "smoking" phenomenon so prevalent in antique radio repair.
::
::Ha ha-
::Terry
::(non compos mentis)
::::Well I went down to check the tube this morning and changed one thing. Yesterday I had the tube tester plugged into the variac because it was close. Today I plugged directly into 120 outlet and the tube tested ok with no change with hand over grid cap. Don't know why the difference but that is the end of this issue. Just won't plug in variac again.
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::
:

The usual emission test is to tie all the grids to the plate and test the tube as a diode. Most of the current goes to the control grid. The purpose of the test is to verify the condition of the cathode. Emission tests stress tubes greatly and should be done quickly. Holding that "test" button down tool long can damage the tube.

:Scott, I don't have a schematic for TC3 but on emission testers usually all elenments grounded except plate. Waas the grid cap lead attached to grid cap? If so it should be grounded with other elements and your hand near it should have no effect. Possibly the grid cap switch/wire open? Does it happen only on that tube (6Q7)? zIf so that position on grid cap may not be closing. PL
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Good emissions testers usually provide adequate resistances so that tubes are never tested under currents stronger than they are designed to handle. Most tube testers use voltages that don't even come near to what many tubes can handle. My particular tester, an EICO 625, tests 6Q7 tubes with an incredibly weak current that would never stress any tube.

Regarding your problem, Scott, be sure that the grid cap is properly soldered to the grid wire, and that the grid isn't picking up stray charges due to a faulty connection. If in question, try another 6Q7.

T.

With the active elements all tied to B+ the control grid takes virtually all the test current. Most testers use 30 v for the test.

:Good emissions testers usually provide adequate resistances so that tubes are never tested under currents stronger than they are designed to handle. Most tube testers use voltages that don't even come near to what many tubes can handle. My particular tester, an EICO 625, tests 6Q7 tubes with an incredibly weak current that would never stress any tube.
:
:Regarding your problem, Scott, be sure that the grid cap is properly soldered to the grid wire, and that the grid isn't picking up stray charges due to a faulty connection. If in question, try another 6Q7.
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:T.
:

...And the test current setting for the 6Q7 is extremely small. On my EICO 625, there is only one setting that'll cause sparks to fly and elements to overheat. It is rarely used. None of the other settings will fry a tube even if you leave it connected for all eternity.

All other sensibly designed testers also limit current values to acceptable levels.

T.