Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: rafe on June 19, 2021, 06:05:10 pm
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I picked this up today and I found a manual online ...but I have a question about the short test . When testing for shorts on 12ax7' and 12au7's the short lamp lights consistantly on the #5 lever ....It has 10 levers and you throw them one at a time to the first position (p) except for the preset 2 levers for the tube (they stay set). These tubes test good and I am thinking it is the nature of the triode tube to show a short on that one setting? Am I wrong I have tested working tubes and It shows a short on 5????
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You probably need to post a photo of the tube tester & the relevant pages of the manual.
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File is to big and I can't reduce the size. I vaguely rember a setting that was a false positive short on triodes on my old tester. I tested a fully operational (Known Good) 12ax7a from my kalamazoo model2 and it showed a short on 5th lever. The manual says to suspect the .02 cap. on the indicator lamp . So my question is if anyone knows if it is triodes in general that show a short on one configuration that is irrelevant? I tested around 8 tubes all the same on 5
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> It has 10 levers
Assume one per pin (covers 4, 5, 6, 7, 8, 9, or 10 pin tubes). Assume no re-numbering.
12AX7 pin 5 is one of three Heater pins. It should connect to 4 and 9.
You could stare at the tester switch until your eyes cross, see if that's what is supposed to be and the chart is wrong. But I would assume your tubes are OK. If they weren't, it would have flamed-out by now.
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(https://i.ebayimg.com/images/g/fsYAAOxyTMdTPceA/s-l1600.jpg)
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Manuals:
https://bama.edebris.com/manuals/superior/tw11/
Scroll halfway down the page.
I don't see the main chart. But it looks like it assumes one of two F pins, and tells you what the other F pin is. However the 12A*7 has three F pins. I think they over-clevered themselves.
BTW, 12AU7 and 12AT7 will short-test exactly the same as 12AX7. The meter reading different, but the shorts all the same. Do they have the same pin settings?
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That is what I was thinking. #4 lever is on f lever #9 is on N then one a a time you throw every lever up to p and light should remain off (when you throw up lever5 it lights up . when you test for quality 4 and 9 stay where they were ...but one side is tested with #2 on p and then the other side is #7 on p....you test both sides of the triode .... You never have two levers on p at the same time. I hope that makes sense . Yes they do have the same settings so does a 5751
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It's just showing continuity not a short? That makes sense
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Ahhh Crap ....that must be what the 5 in Phil. Cont. row means ....I'm laughing at myself ....so you can laugh too PRR
:l2:
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The "short" test is a neon lamp. Anything much under a few hundred K-ohms will light the light. Most electrodes will show >100Meg between them, no visible light. But it sure can't tell 5 Ohms from "zero Ohms" (whatever that is); it won't know a healthy heater from a bolted short.
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How about the 1/4 inch jack for noise ...Is there any value in using that ? It seems like a decent tester and it is in pristine condition .....Maybe mid or late 50's not sure