I found an old early 1960 oscilloscope ELCO 460. I would like to get it working and this is what it is doing.... it powers up all the knobs seem to work and do what they are supposed to according to the manual but after 5-10 minutes all I get is a flat line. I am wondering if it is a tube or something in the circuit. I tried to find a place to test tubes and no luck, when I was a kid they were everywhere. The scope is in amazing condition and I believe it was always stored in a climate controlled building. I am a newbe with regard to old circuits.... any thought would be appreciated.

 

Welcome to AAC!

What type of signal are you trying to measure? AC? DC? How is the coupling set on the scope?

 

Does the scope have a calibration signal; if not what kind of a signal are you putting into it. Include info on connections and settings if you want an intelligent answer.

 

I have not tried to really measure anything yet, just wanted to get it working. Not sure what is meant by the coupling set.

 

I have not tried to really measure anything yet

With no input signal, all you get is a flat trace; if you have sweep and trigger set correctly.

Not sure what is meant by the coupling set.

You can AC or DC couple. DC lets DC from the signal pass through; AC will block it.

Your vertical amplifier knob appears to have a calibrator setting. If you set it to calibrate, you should see a 60Hz sine wave 400mV peak to peak.

 

The obvious answer is that the vertical deflection amplifier is failing after warm-up, but "obvious" doesn't mean, "correct".
I suspect that the first scope I ever assembled from a kit was similar, but I can't remember the schematic from 1964.
Have you any way to post the schematic?

 

The obvious answer is that the vertical deflection amplifier is failing after warm-up, but "obvious" doesn't mean, "correct".
I suspect that the first scope I ever assembled from a kit was similar, but I can't remember the schematic from 1964.
Have you any way to post the schematic?

I have found that after about 30 min the screen is void of any signal ... the V Pos is all the way to the right and the signal lines were never in the center. I will look for the schematic and post an image ... might take me awhile, thanks

 

 

the V Pos is all the way to the right and the signal lines were never in the center.

Again, this points to the vertical deflection amplifier. It's not centered and it fails completely after some time.

 

C14.......

 

C14.......

Here is what I have for this scope

 

Perhaps I should elaborate.
Go poking around C14 in a quest to measure voltages and diagnose the failure, or just replace it and see what happens.
a 50 year old Aluminum electrolytic capacitor is a prime suspect in any design!

If anybody can say why I guessed the wrong section of the innards, speak up.

 

Note that in schematics this old, mFd is microfarads, (you'll see uF or μF on more recent schematics/parts lists).

 

Depending on how/where it was stored, the copper can have a black "soot" on it. some people jump to the conclusion that this is carbon but it is usually black copper (II) oxide. Some cheap pots and switches/selector knobs like you'll find in Eico and Knight test equipment develop shorts across the wiper. Some sprays are available but success is hit/miss. Good luck. Your time may be better spent getting a dead Techtronix working if your first few attempts fail.

 

Also, you can bring your tubes down to the RadioShack or most Hardware stores and have them tested... Wait, I think a 40-year old memory just escaped.

 

You have a trace on the screen, that's good.
You have a schematic, that's even better.

I would say that you have a good chance of reviving that ol' boat anchor with a little bit of help from your friends at AAC.
Don't despair and don't rush into it. Take your time and tackle one issue at a time.
I would say that your tubes are likely to be good. Pay attention to the electrolytic capacitors first.

Do you have access to a working oscilloscope?

If not, a DMM will do for now.

 

The first thing I would check is the rectifier outputs.

 

You have a trace on the screen, that's good.
You have a schematic, that's even better.

I would say that you have a good chance of reviving that ol' boat anchor with a little bit of help from your friends at AAC.
Don't despair and don't rush into it. Take your time and tackle one issue at a time.
I would say that your tubes are likely to be good. Pay attention to the electrolytic capacitors first.

Do you have access to a working oscilloscope?

If not, a DMM will do for now.

No working oscilloscope but good at poking around.... one of the tubes produces 1,000v so I will make sure it has been unplugged awhile. I am retired so time I have.

 

Let's see where we're at.

You have a trace on the scope. (If you touch the tip of the probe with your finger you get squiggly line?)
After 5-10 mins you have a flat line.
After 30 mins the flat line drops off the bottom of the screen?

So you have imbalance in the vertical amplifier.
Unplug V1, 6AU8 and V2, 6AU8 and tell us what happens.

Remember which tube you pulled from which socket.
(We will swap the two in a minute.)

 

Let's see where we're at.

You have a trace on the scope. (If you touch the tip of the probe with your finger you get squiggly line?)
After 5-10 mins you have a flat line.
After 30 mins the flat line drops off the bottom of the screen?

So you have imbalance in the vertical amplifier.
Unplug V1, 6AU8 and V2, 6AU8 and tell us what happens.

Remember which tube you pulled from which socket.
(We will swap the two in a minute.)

Both tubes removed.... on startup a dot comes on and goes out then just a blank screen.