New project - 1967 oscilloscope restoration

[(*steve*)]

Ok @73's de Edd, here's some voltages, all with respect to the chassis.

The heater windings (pins 1 and 11) are at -515V and -513V respectively. Pin 11 is tied to pin 2

The cathode (pin 3) is around 7V more positive than the heater due to the voltage drop across the 100kΩ cathode resistor (current is approx 70μA).

G1 (pin 2) is tied to the EHT and is also at -515V

A1 (pin 4) is at -303V

The deflection plates on pins 5 and 6 are at 188V and 184V respectively.

A2/G2 (pin 7) is at 88V

The deflection plates on pins 8 and 9 are at 180V and 189V respectively.

Pin 10 is N.C.

And we're back to pin 11 that was mentioned above.

The scope is in external timebase mode (effectively X-Y mode) with no signal and the trace is roughly centered (it's actually about 1/2 a division low and 1/5 of a division right)

If I move the trace all the way to the top of the screen, the collages on the delection plates do this:

5: 197V
6: 165V
8: 179V
9: 184V

All the way to the bottom

5: 167V
6: 195V
8: 179V
9: 183V

All the way to the left

5: 182V
6: 181V
8: 156V
9: 203V

And finally, all the way to the right

5: 182V
6: 181V
8: 199V
9: 160V

Ok, and as I check the positions of the astigmatism and focus controls, I find they're labeled back to front!!!! AND knowing this I can adjust the trace to a fine point!



The spot is a bit blown out in this image, it actually looks quite small.

Turning on the horizontal timebase we get this



And with a little tweak to the horizontal gain...



Woo hoo!

Now to rotate the tube a little too get the trace horizontal.

 

[(*steve*)]

I'm pretty happy with that



I might grab a signal generator to see how well it works, but I really need to replace the line cord and put a plug on it before I do too much more.

I'm pretty sure this isn't up to code

 

[(*steve*)]

Well, it does show a square wave.

 

[(*steve*)]

Hmmmm, but sine and sawtooth doesn't look at all good





I suspect a problem in the vertical amplifier.

 

[bertus]

Hello,

That certainly looks like clipping on the lower side.

Bertus

 

[BobK]

Wow, impressive progress!

Bob

 

[(*steve*)]

Damn, it seems to be working now :-(



It seems like it was a switch contact issue because it went away after changing the vertical range a few times.

 

[BobK]

So, what are you going to do with it now?

Bob

 

[(*steve*)]

I was going to convert it to a component tester.

However some tests I've done in X-Y mode concern me a little. I think there may still be some fault hiding in there.

Changes in the gain of the vertical amplifier seem to have an effect on the position of the trace. This needs more troubleshooting.

The control at the rear clearly gives a few options for triggering, but the triggering doesn't behave like you would expect. I think that may be a feature though.

 

[BobK]

Changes in the gain of the vertical amplifier seem to have an effect on the position of the trace. This needs more troubleshooting.

I think a DC offset in the vertical amp would do that, right? Is there possibly a trimmer to null the offset?

Bob

 

[(*steve*)]

There are a few adjustments, but they seem to be trimmer capacitors. Also, the input is always capacitively coupled, so I don't see any reason why the coupling between the vertical amplifier and the differential delection plate driver isn't likewise capacitively coupled (but I haven't checked in any detail). Something to consider...

 

[BobK]

Hmm... Never seen a scope that did not have a DC input option, but you have found one!

Bob