Found some strange part in a Tektronix 2336 and would like to know more about...

[Geronimo]

Got today my latest “for parts only” purchase from the US, the famous Tektronix 2336YA and had a first look inside just to make sure it doesn’t show any obvious damage and will blow my breaker on the first try. This is my 3rd one of this series which I all got from a surplus sale on eBay.

Some would say it is not only too risky to buy such “sold as-is” and untested parts and when considering the customs tax and horrendous shipping costs, I doubt I will do it once more. This specific model however is mostly unknown and unavailable in Germany and I like it not just because of its rarity but also because I’m kind of attracted to the old analog CRO’s and had always luck to be able to repair this particular type. This one is working fine OOTB, the Caps seem to have been replaced already and it only shows some small flickering on the inserted signal from my SG.

However, the point of this post is to show what I found inside and have never seen bevor: Right next to the fan in the back rear and connected to the 5V rail which supplies power to the adjustment for the A and B slope offset is a additional PCB with a part I’ve never seen.

The PCB shown on the attached picture has the following numbers written on: “+5”, “G-8533-01” and “G70-8368” underneath the tube. Someone also scratched “409/2780” as far as I can read it bevor the green coating came on top of the PCB. On the back of the PCB is nothing as it is a single layer type.

Beside the “0”, “2500” and “5000 hrs” markings on the scale of the tube there is, I guess the manufacturer of the tube device named: “The fredericks company” “P/N 8005”. The top and thicker connector is also marked as “+” while the lower one is marked “-“, accordingly the device was connected to the 5 volts rail. Beside of the hours marking this all is hard to see as it is basically underneath the tube thing and facing the PCB.

The little resistor reads 353 KOhms (357 according to the color code), the tube itself reads 2.7 (on my PeakTech 2170) or 5.6 KOhms (on my Fluke 45), don’t know why.
As you can see on the second and third picture inside the tube is a kind of a pipe which holds a little copper wire like piece which is now stuck at the bottom and on the “0 hrs” scale. The tube thing looks like being filled with something but there is no bubbles to see when I move it. I can’t neither shake the copper thing away or move it when I turn the part around or hit it on the table.

What is this tube-like device?
Is this a kind of usage hours meter and is it now showing the device was used more the 5000 hours?

If I read the IC’s right in this scope, it was built around 1988.

My first Tektronix 2335 which I easily repaired and sold to a colleague had nothing like this inside and the other 2336 waiting for repair neither. Was this “bodge” thing put it by some service provider who wanted to know the total usage time for this oscilloscope? Should I try to put 5V in reverse order of what is shown on its marking? Has anyone ever seen this particular part or a similar one?
The scope as I said is working and obviously this part has nothing to do with its intended capabilities. I wonder if this is a known thing and why it was put inside this machine. Anyone any idea?

Cheers,
Geronimo

[CaptDon]

Google up 'Capillary Hour Meter'. It looks like one of those.
500 hours max sure isn't very long of a run time. The capillary
movement (like a thermometer) is controlled by the resistor.
You can make them move faster or slower by changing the
resistor value. Some can actually even run backwards by
changing the polarity of voltage on them.

[shakalnokturn]

The good old days before RTC's and firmware runtime counters...

[coromonadalix]

yep  its  a time counter,  just found one yesterday in my racal dana 1992 hz counter

[Gyro]

Unfortunately it has 'run off the end of the scale'.  Normally, while the mercury column index has some time to run, you can reverse the polarity and the index will run back in the opposite direction.  Once the electrode is exposed though, I think the electrolysis renders the tube useless, but you could always try turning it round for the hell of it. It won't cause any harm.

Edit: Some data attached.

[jdragoset]

Got two from Ebay
https://www.ebay.com/itm/800S-HOUR-METER-TOTAL-5000-HRS-AC-DC-8VOLTS-MIN-700-MAX-NEW-OLD-STOCK/291188909856?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
They appear to not use mercury but a copper indicator with a column of copper sulfate that deposits copper on top and dissolves copper from the bottom.
https://en.wikipedia.org/wiki/Copper_coulometer.
The one pictured appears to be at zero hours and was possibly never energized.

[Geronimo]

Aha!
Now it all starts to make sense for me.

I guess inside the capillar pipe is an electrolyte which limits the amout of energy passing the tube. Teh added resistor counts too in this regard.
This type does not have any mercury inside so it should be safe and cause no poisoning in case.

Applying some voltage in reverse polarity has not much of an effect. The only noticeable chnage is some dark cloudy stuff now settling at te top of the copper pice.
At the beginning I could rise the current up to around 2 amps max and now it is basically zero even at 15 volts.

In fact the 5000 hours count is only worth 208.3 days thereof less then a normal working year.
Maybe the intention was to check the usage time for doing some re-calibration on a specific interval.
Attached is one last picture from the backside.

The one mentioned on ebay has the same appearance as mine, the piece of copper is at the zero hours marking. I guess the device counts backward starting at 5000 hours.

Cheers,
Geronimo

[jdragoset]

357 k ohm series with 5 volt rail = 10 to 15 microamps.
These were often installed in military equipment, where 5000 hrs maintenance would include replacement
with a new device.

[WastelandTek]

This forum is great!  just ran into one of these in an HP 3586C and had no idea what it was.  Not only was the entire 5000 hour column shiny copper but galvanic corrosion had been eating away the far cap and fuse  holder for some time.  I always love it when I google something and the best answer pops up in one of my home forums.

Thanks guys!

[Chris56000]

Hi!

The Handbook for one of my British Made Cossor 4100 Oscilloscopes documents this as "E.T.M." (Elapsed Time Meter) and shows it both on the power supply circuit diagram and the component layout – this is usually always an added item that's rarely mentioned in manufacturer's documentation!

RS Components used to sell the "mercury–in–liquid" type with a graduated but unnumbered scale – there was a formula provided so you could calculate how many maximum hours you wanted it to run for, adjustable with the series feed resistor!

There are also mechanical digital and electronic E.T.M. units available from various sources, but these are mostly too large or far too expensive for anything but the most reliable scientific or military gear that has to have a traceable maintenance record!

Chris Williams

[David Hess]

The Tektronix catalog literally says:

"2336YA Oscilloscope with delta Time, Elapsed Time Meter, Extra Accessories and Manuals"