anicent tube Oscilloscope Repair

[Supercharged]

A while ago i bought a Siemens "Oscillar". It worked fine for some time but one time when i turned it on the magic smoke escaped . This wasn't ordinary magic smoke however. It literally smelled like sh*t.
So since it wouldn't do anything i suspected a Power supply fault, and sure enough i measured a dead short across one Cap, which took out a Selenium rectifier (see picture 1). It didn't have any blow marks on it, but my knowledge on chemistry was enough to know, that selenium is able to stink horrifically. So i replaced The cap (with 2 caps in series, with balancing resistors) and all of the rectifiers, since i didn't want the horrible smell again if another one failed. Doing this however is easier said than done, since one can't just mount different components on a PCB, just because there isn't a single PCB in there. So i glued the rectifiers to the case, where the old ones were. The caps i culdn't just glue in place, so i 3D printed a hold down plate and secured it with a zip tie (Picture 2 and 3). And voila it works again.

I just posted this here, because I thought some people might find this interesting.

[MickM]

Hi;
  watch out - your HV is now much higher.
Normally a dropping resistor is added in series to bring it back down.
If you don't have schematics look at the electrolytics connected to the diode for working voltage, then subtract a third.

Mick M.

edit:
Also when that was sold the line voltage from the wall was probably 105-110 VAC
I just measured mine at 123 VAC.
Seleniums drop about a volt per fin, silicon 0.7v.
Try 100 Ohms at 5W.

The electrolytics should also be changed, along with any wax/paper caps.

[james_s]

The worst smell I've ever smelled in my life was from a selenium rectifier burning up. Blech!

[Supercharged]

Hi;
  watch out - your HV is now much higher.
Normally a dropping resistor is added in series to bring it back down.
If you don't have schematics look at the electrolytics connected to the diode for working voltage, then subtract a third.

Mick M.

edit:
Also when that was sold the line voltage from the wall was probably 105-110 VAC
I just measured mine at 123 VAC.
Seleniums drop about a volt per fin, silicon 0.7v.
Try 100 Ohms at 5W.

The electrolytics should also be changed, along with any wax/paper caps.

I do have the scematics (atached), i actually aded a 100 Ohm Resistor, problem was i thought a quarter watt would do the trick and yes i was wrong , so i took them off. For now it seams fine but i might put some higher wattage resistors back on if i can be bothered. and don't worry about potential damage to caps they are all rated way above even maximum Voltage.

PS I'm from swizerland so our Grid runs at 230V and this scope is switched to that.