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Old 02-17-2019, 05:51 PM   #1
eccerr0r
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Default [emission only] vacuum tube tester safety

Well, I was able to acquire a vacuum tube tester. It's a cheap crappy emission only (i.e., no transconductance/mutual resistance) tester - but I realized it was even crappier than I thought. The power supply is an autotransformer, and the "floating wire" top cap lead has an electrical path to line power! Touch the cap wire, get electrocuted!

I would suspect all those old console tube testers were isolated especially if it had one of those flying top cap leads... or at least I hope it would. This one is indeed cheap cheap cheap, alas it does get the job done...
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Old 02-17-2019, 06:04 PM   #2
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Default Re: [emission only] vacuum tube tester safety

well i suspect it's normal, back in tube days tv's & radio's where often live.
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Old 02-17-2019, 06:21 PM   #3
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Default Re: [emission only] vacuum tube tester safety

They did have live chassis like the AA5 but you can't touch any part of the live portion with your finger... but in this case if the tube cap wire touches something, it could be quite problematic...
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Old 02-17-2019, 06:51 PM   #4
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Default Re: [emission only] vacuum tube tester safety

that's not completely true, you could touch the antenna connector etc at the rear - and with a 2pin plug you have a 50/50 chance of winning!!
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Old 02-17-2019, 06:58 PM   #5
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Default Re: [emission only] vacuum tube tester safety

I thought AA5's had internal loop antennas, if not, they are capacitive coupled with a really small capacitor (so that any leakage would be less than ~1mA to GND at 60Hz)?
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Old 02-18-2019, 07:07 AM   #6
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Default Re: [emission only] vacuum tube tester safety

go watch some "carlson's lab" vids - it will put you off old stuff forever!!
he had a chrome plated radio the other day, plug it in the wrong way and the whole shell can go live - and it did!!!
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Old 02-18-2019, 10:51 AM   #7
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Default Re: [emission only] vacuum tube tester safety

If things like this were fine back then and modern CCC/poor design is not, what has gotten into us???

Hooray...found some broken vacuum tubes, at least my stockpile of vacuum tubes is going down, no sense in keeping the bad tubes...

Last edited by eccerr0r; 02-18-2019 at 11:20 AM..
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Old 02-18-2019, 11:35 AM   #8
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Default Re: [emission only] vacuum tube tester safety

it's down to education.
in the past people simply knew that you dont touch metal bits when something is on!

also, people used to do risky shit a lot more.
fixing a fuse with the foil from a pack of smokes was so common that it was more likely than a working fuse!!!
2way adapter?? no, just poke the wires into the wall and smash the plug into the socket over them - saw that a lot.

and my fav'
making an extended cable by twisting the wires and wrapping it in tape.
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Old 02-18-2019, 04:28 PM   #9
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Default Re: [emission only] vacuum tube tester safety

I wonder if I could hack this tube tester to do transconductance tests by feeding some signal into the grid... :o
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Old 02-18-2019, 07:56 PM   #10
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Default Re: [emission only] vacuum tube tester safety

well you can find schematics for most B&K gear - so your only limited by time & patience.
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Old 02-27-2019, 08:50 AM   #11
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Default Re: [emission only] vacuum tube tester safety

The ones I remember all had a power trans. I remember the days when some of the gorcery stores had a tube tester . Found these links for you .
https://fairradio.com/?s=+tube+tester+
https://www.ebay.com/sch/i.html?_fro...ester&_sacat=0
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Old 03-08-2019, 06:12 AM   #12
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Default Re: [emission only] vacuum tube tester safety

Surely any electronics lab (apart from where you are working solely on low voltage devices) should have an mains isolation transformer powering the test bench. They are not even expensive
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Old 05-07-2019, 06:32 AM   #13
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Default Re: [emission only] vacuum tube tester safety

this set must have been missing its isolation hardware.
not unusual for these parts to have degraded in the last 70+ years and replaced with metal parts by someone who did not understand why the chassis mounts were made of "cheap" plastic or rubber.
or used a metal knob in place of a plastic one.
aa5 sets require a bit of caution when testing/repairing them.

Quote:
Originally Posted by stj View Post
go watch some "carlson's lab" vids - it will put you off old stuff forever!!
he had a chrome plated radio the other day, plug it in the wrong way and the whole shell can go live - and it did!!!
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