the youtube algorithm works in strange ways i recently did a video about cassette tapes
which plenty of people my age who grew up in the '80s and '90s would have memories of and
experience with but it turns out the largest group of people watching that video were senior citizens
then i did a video about records which are over 100 years old which virtually
no human beings on earth are old enough to have memories of when these things were new
but yet plenty of people in their 20s and 30s watched that video
so since young people seem to like really old stuff this little thing definitely caught my
eye when i saw it in a thrift store recently it is a circuit tester measuring ohms and it definitely
looks very very old it's a rather worn metal case with two screws on top for attaching the terminals
there's a little adjustment up there for zeroing the meter
on the back the original owner scratched in his name
tom woods this is something that people did a lot before label makers were invented
and it comes with directions on another metal plate attached to the metal case so this thing
is entirely metal and this faceplate for the meter is definitely glass so it's probably not
a single piece of plastic in this entire thing i thought this would have been made
of bethlehem steel but it turns out it's not magnetic so i think this entire thing
is painted brass you can see it showing through there where the paint has worn away
directions connect instrument directly to circuit no external battery required needle should point
to zero when posts are short-circuited as battery weakens short circuit posts and bring
pointer to zero by turning screw located between posts to renew cell unscrew instruction plate
insert new cell and adjust to zero and it was made by roller smith in bethlehem pennsylvania
this one has a range of zero to ten thousand ohms and then
the end of the scale is infinite and i love that needle on the meter the movement is nice and free
it says don't use for testing blasting caps or blasting circuits because obviously this
thing puts some voltage across whatever you're testing so you don't want to put that across
an explosive device otherwise it may ignite in fact they can even sometimes ignite by radio
signals i haven't seen them in a long time but i remember seeing signs along the road saying not
to use your two-way radio like a cb radio or ham radio because they were doing blasting in the area
i tried to find the history of the roller smith company
they were based in new york city and they had their factory in bethlehem pennsylvania
it seems like their heyday was back in the 1920s and 1930s because that's when
most of the information i can find about them is from this ad from 1932 and it's announcing their
type htd-2 circuit tester in meter which is very similar to the one i have except it's larger and
has a switchable low and high range they say it runs on a renewable standard flashlight
cell with flashlight spelled as two words they say the circuit tester is the most useful instrument
that can be imagined and any and everyone who has occasion to test circuits for continuity and
resistance should have one they don't mention the price but they say the price is surprisingly low
roller smith products comprise complete lines of electrical instruments
indicating in graphic relays air and oil circuit breakers and control panels
hopefully nobody left old batteries in this so i'm going to
unscrew this direction plate and see what's inside although i'm actually
hoping there's some kind of vintage battery in this that would be very interesting to look at
because often those old batteries don't actually leak that much
they just kind of silently go dead okay there's the screws removed
there's the instruction plate
and inside there's nothing so thank you tom woods for removing the battery the last time you use
this so it looks like that would fit a c-cell battery but i want to see more of that meter so
i'm going to take off the rest of the faceplate i removed the screws so now here is the reveal
that comes off with the glass attached to it and that definitely is a piece of glass
and not a whole lot more that we can see but we can see the meter movement
oh there it is type htd so the ad was for the htd-2 so if this is the original htd that means
it's even older than 1932 unless they continue selling it alongside the htd2 number 544164
made in usa of course np-2186
i'm not going to take this meter apart because i don't want to mess up the calibration but
definitely a nice vintage meter
and no corrosion on the battery terminals maybe a little bit of green stuff on the negative
but nice and clean brass terminals that one has a plus mark on it so i'm going to put in a new
c cell battery here's a c cell battery made by rayovac it was made in the usa
they're another company that's been around for a long time so let's see is this going to fit
so the battery is installed now let's put it back together and see if it works i just attached some
clip leads nothing fancy so let's see if it works aha it does i like that movement of that meter
the way it bounces around that's nice now let's zero that meter setting now i'm going to follow
the instructions to short circuit the leads and adjust the trimmer on top until it reads zero
well
doesn't seem to make much difference oh it's going down a little bit
that battery i put in wasn't the strongest so that may be why it's not reading all the way to zero
so let me get a brand new battery in there and see if that makes a difference
a new battery has been installed and don't tell anyone it's actually a AA cell wedged in there
because i don't have any good c cells left and now if i short look at the terminals
it's actually going off the end of the scale so i have to
turn down the rheostat until it reads zero on the meter there it goes right about there
now i have some resistors to test measuring i'll start with a 100 ohm resistor and
it's showing about 95 ohms and that is a 5% tolerance resistor so that is in tolerance
even on this 90 plus year old meter so that's good here is a 380 ohm resistor
and that's reading let's see that's
200 300 400 so that's oh that's perfect right on the money there 380 ohms
next is a 1k resistor
and again right on the money a thousand ohms
now the scale is getting more bunched up as i go
higher in value so it's going to get a little less accurate and more difficult to read
but that's just the way these meters were this is a 4.7k resistor and it's pointing right at 5000
so within the tolerance of that little bit of range that's pretty good
and finally this is going to be right at the end of the scale
a 10k resistor the meter should just barely move oops oh did i
i thought that was 10k it's actually another 1k resistor my bad well the meter showed me
okay this should be a 10k resistor brown black orange and then gold for 5% tolerance
so put that into the terminals and yeah it just barely moves
pointing at pretty much right on the 10000 mark so this 90 or more year old meter is working
perfectly now here's a 5k potentiometer so if i measure across the whole thing it should read
5k as it pretty much does and if i attach it like this we should get a range of motion on the meter
as i adjust it
turn it up and the resistance increases
here's a 1k potentiometer so across the whole thing we get 1k and now we get our range of
motion up to 1k you can even see it's scratchy it makes it makes the meter bounce a little bit
yeah this pot hasn't been used in a while
that's why it's bouncing around because it's a scratchy pot and here's an oddity a 10 ohm
potentiometer it's probably the lowest value potentiometer you'll ever see so if i connect that
yep 10 ohms and for what it's worth we should get motion between 10 and zero again a scratchy pot so
that's all you get from zero to ten ohms here's a 500 ohm impedance dynamic microphone
and when i measure across it
we get 450 ohms so that's pretty close and here is a 4 ohm impedance speaker and measuring it it's
showing exactly 4 ohms on the meter now i have it connected across a small dc motor and as i
twist the motor you can see the needle swings so that's interesting oh and if i rotate it the
opposite way you can see the the meter moves to the left and this way it moves to the right
so this has been a look at and test of the roller smith htd circuit tester an ohmmeter
probably from the 1930s so it's around ninety years old and still working perfectly