Now for a small relief.
Klein+Hummel Röhrenvoltmeter (VTVM) RV-12. According to radiomuseum.org it is of 1962 vintage.
Which company dealing with electronics did
not offer their interpretation of the (presumably) same basic design?
Klein+Hummel, makers of studio and HiFi ecquipment, were assimilated in 2009 by Sennheiser, but they had and still have an excellent reputation.
You guessed right this time, again with the boring 10 V reference:
![](https://i.imgur.com/jSFJwNE.jpg)
Note that the necessary 1 MΩ resistance is inserted. That looks rather good.
Resistances measurements are, well forget it. The needle points in the general direction of the value, but that's it.
The back of the steel case hasn't much to show but the single screw that holds it all together and the fuse holder/voltage selector and the power switch. Power cords were usually not detachable in those days. Which I don't like, as they need extra room when storing the device and they tend to tangle up with others.
![](https://i.imgur.com/Fusd2wy.jpg)
Not too many surprises inside at first look, dust & rust:
![](https://i.imgur.com/ZUOseOs.jpg)
Of course, after umpteen years in storage, the battery for Ohms draws some interest:
That is surely an 'interesting' design of a battery holder! The resistor is directly soldered to the battery cell. The clamp is fixed. The strain relief of the power cord can also be seen. I guess that is not the original technique.
The battery with the plastic spacer (or collar) and a
slightly rusty spring.
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif.pagespeed.ce._hfWAz_QHO.gif)
![](https://i.imgur.com/PfRiATD.jpg)
Despite some rust, that 20 year old battery did not leak and is still as good as new. Anyway, I decide to forget about Ohms here altogether, so I don't have to worry about the battery. If need be, I have means to measure resistance.
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/xwink.gif.pagespeed.ic.cldandycH0.png)
Although this machine is heavy metal inside out, it is not connected to protective earth. Looking at the flimsy insulation of the transformers primary wires (mustn't they be doubly insulated for Protection Class II?) sends a slight shiver up my spine. But then, why should they suddenly make a short to the chassis? That case is quite effective in protecting them.
And here is my second RV 12 (without dash), likely somewhat newer (and these knobs are never ever original!). Alas, it's movement window is shattered. And the measurement is noticeably off:
![](https://i.imgur.com/I2qp3YY.jpg)
With this, there are signs of a previous battery leakage (but no battery). The power cord is certainly not the original (it looks like typical Telefunken) and there is absolutely no strain relief whatsoever!
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
![](https://i.imgur.com/DvFZKGx.jpg)
The back either shows the instrument's schizophrenia, as it says 'RV-11', or they got swapped at birth.
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/xgrin.gif.pagespeed.ic.QVVz6XIT20.png)
![](https://i.imgur.com/oZwuq6n.jpg)