What is this thing?

[electroking]

Originally Posted by jr_tech

I really doubt that any decent modern meter presents a danger to battery tube filaments. Most of these require a filament current of 150 milliamps to operate, although some tiny hearing aid tubes require only 20 or 50 milliamps. I spot checked a couple of modern DMMs and found that they only supply less than 1/2 milliamp to measure ohms... not a problem! Although many DMMs are *powered * by a 9 Volt battery, the current supplied for resistance measurement is indeed quite small.

I have no doubt that somebody at some time, using a very primitive ohm meter did, indeed blow a filament of a battery tube (I have read the same warnings before in old electronics magazines), but it is highly unlikely with decent modern meters.

If concerned, simply *measure* the amperage delivered by your ohm meter in various ohm ranges.

jr

Most of the battery type tubes (such as 1R5, 1T4, 1U4, 1U5, etc.)
have 50-mA heaters. Just connect your ohmmeter to a milliammeter
of adequate range to check the current supplied.

[jr_tech]

Originally Posted by electroking

Most of the battery type tubes (such as 1R5, 1T4, 1U4, 1U5, etc.)
have 50-mA heaters.

OOPS! I grabbed a common portable radio tube, a 1R5 and looked it up, knowing that all of these common tubes draw the same current. Unfortunately, I read the current for the tube above in the manual, a 1R4 which does indeed draw 150 ma heater current.

The conclusion is still the same, these battery radio tubes draw far more current than a a modern DMM can deliver when measuring ohms.

jr