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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Thu 15, 2019 7:52 pm 
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Location: Powell River BC Canada
You have a good point. Perhaps the standalone would be better. Smoke in
a 470 is probably very hard to walk back.

Techs working in systems will have the big picture running in their heads.

Like a pitcher with runners on the bases. :D

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Thu 15, 2019 8:09 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
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Location: St. Louis, MO
Eh, you're no fun. This box is gigantic with that 7" tube. PLENTY of room for smoke!

You know, I got a Accurate 153 signal generator sitting here on my desk. I just noticed on the schematic that its primary transformer has a 6.3V winding on it, and it already has a power cord hooked up. I may just need to separate the whole transformer out of circuit and see if it works... For testing, obviously.


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Fri 16, 2019 3:05 am 
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Location: Lincoln City, OR 97367
Greetings to ZombieElvis and the Forum:

Your scope is AC coupled only, so provided you are careful, you can use the scope filament winding. Just be sure that you don't connect the hot side of the filament winding to the ground side of your scope input or you will fry the power transformer. In case of doubt, use a separate transformer.

I didn't simulate the entire input circuit because it is so hard to import extra subckt files into LTSpice. The cal circuit couples energy into the grid of V101 in a slightly different manner than the actual scope input. Otherwise, you could just set R108 for a specific voltage at the junction of R101,R102 and R103 and you would be calibrated. Unfortunately, I don't know what that voltage is supposed to be. Since the grid is a high Z point, I suppose I could simulate the circuit using an op-amp instead of a tube and come pretty close.

If I get ambitious, perhaps I will. In the meanwhile, the external transformer trick should work well depending on the accuracy of your meter.

To answer your question, you are feeding the scope vertical input with a known signal, which you can set to 10 divisions using the scope vertical gain. Once you have set the vertical gain to 10 divisions, the scope is now "calibrated" using an external reference. Therefore, if you do not change the vertical gain setting but merely switch to "Calibrate" mode, then you have a means to compare the R108 reference signal with the external reference signal. Adjust R108 for the same vertical deflection as the external calibrated signal source or 10 divisions. As long as your meter (the standard) reads 177 mV, then the external standard is correct. You can then switch back and forth between the cal signal and the X1 signal and compare the internal cal signal to the external cal signal. If R108 is set correctly, there should be no change in amplitude when switching back and forth between the two.

After you have set R108 correctly, it will not be necessary to have an external standard handy to set the scope vertical gain to read actual voltage. The internal cal signal is now correct and can be used for this purpose as the designers intended.

Regards,

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Fri 16, 2019 5:52 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Quote: "you can use the scope filament winding."

There are four filament windings in the scope.

Three of them will zap you into an acute awareness state. 8)

Only the one that is connected to the panel lamp can be used.

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Fri 16, 2019 10:21 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
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Location: St. Louis, MO
How sure are you about that 177mV, Jthorusen? I'm still off by 4 divisions and R108 is at max ohms. I can't adjust it any farther.

177 mV at 10 vertical divisions

switched over to CAL, R108 turned to max

I double checked R107 as well. It's in spec.


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sat 17, 2019 12:42 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Sin wave scope displays are peak to peak.

When an AC voltage is quoted, in this context, are you meaning RMS or P-P ?

177 mV RMS is ~ 0.5 p-p

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sat 17, 2019 2:13 am 
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Greetings to ZombieElvis and the Forum:

I added an op amp to the circuit to simulate the high Z input impedance to the grid and the answer comes out the same.... 1/2 volt peak-to-peak or 177 mV RMS.

One thought occurs.... when in the cal mode, the scope does NOT disconnect the probe input from the vertical amplifier. Since you have a third wafer on your new S101, you might think about adding this function. If you still have the external 177 mV reference connected to the scope input when you switch to calibrate, what you will see is the algebraic sum of the two signals. Since they are unlikely to be exactly in phase, the result will not be exactly 1 volt peak-to-peak or four major divisions.

Be sure you disconnect the 177 mV standard when you switch to calibrate mode. This is not as convenient as just rotating the input switch and I am surprised that Eico didn't disconnect the input when in Cal mode, but then, it is a cheap scope. I didn't notice this earlier or I would have told you to disconnect the external input.

Regards

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sat 17, 2019 5:48 am 
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Location: St. Louis, MO
Umm... check the pictures again. I actually disconnected the probe for the CAL test. Sorry I didn't mention it.

Do I need to check the voltage coming off of S101 to see if it actually is 500 mV peak to peak?


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sat 17, 2019 6:28 am 
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Greetings to ZombieElvis and the Forum:

I'm not sure where I was with the simulation... I had the pot set for 5K and the voltage was just a bit over .5 V peal-to-peak. Choice of op-amp also influences the result slightly.

Anyway, here's a simplified procedure. The calibrate circuit can produce 1 V peak-to-peak. This will occur with R108 set to near its minimum value. This is 1/2 volt peak or 354 millivolts RMS. Just connect your meter to the junction of R106 and R107 and set R108 for 354 mV RMS. This should give you a 1 volt peak-to-peak cal signal. You can then set the scope gain for whatever number of divisions is convenient for 1 V peak-to-peak. 1 division would be 1V/div. 2 divisions would be 1/2 volt/div. etc.

Check the calibration against your external standard set to 354 mV RMS. The number of scope divisions should be the same.

Regards,

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sat 17, 2019 10:21 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11995
Location: Powell River BC Canada
I don't think the operating manual for the 470 has been found, but
one option for horizontal input is 60 Hz. from the phasing control.

With S101 in calibrate and line sweep selected, the scope will display
a lissajous figure shape controlled by the phasing knob.

An addendum in the assembly manual mentions a wiring error for S -101.

The vertical sensitivity for your scope is 0.01 RMS volts per inch, amplifier,
and 15 RMS volts per inch direct connected. (rear access panel)
Attachment:
Eico 470 construction addendum.jpg
Eico 470 construction addendum.jpg [ 161.82 KiB | Viewed 1833 times ]

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Amateur Radio Literacy Club. May we help you read better.
Steve Dow
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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Sun 18, 2019 7:58 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 422
Location: St. Louis, MO
It wasn't a wiring error. The error was in the picture, hence the updated picture. The 2 source contacts were reversed. The point is moot anyway since I had to replace that entire switch. Yes, I was extra careful to match up wires and components to the correct contacts on the new switch.

Hooray! I was finally able to get something adjusted correctly! I had to do this one on its side since the shielding made it hard to reach the R106/R107 junction.
354mV from R106/R107 junction to ground in CAL mode, no probe

354mV from outside transformer in 1X mode

Am I done adjusting R108 now? If so, then that just leaves the 2 trimmers for 10X and 100X attenuation modes. Is that similar to the 460? That manual says to short Sawtooth to V Input, adjust the knobs, then adjust the respective trimmer caps until the diagonal line is straight.


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Mon 19, 2019 1:46 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11995
Location: Powell River BC Canada
Have you taken into account the effect of the declination of the earth's magnetic field
which can require readjustment of the scope's beam positioning controls ?

Things happen when CROs are turned on their sides. :D

Things seem to be going well with your scope.
Attachment:
Dipping Needle.jpg
Dipping Needle.jpg [ 282.99 KiB | Viewed 1794 times ]

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Mon 19, 2019 8:13 am 
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Greetings to ZombieElvis and the Forum:

It would seem that you now have your scope calibrated. The calibrator waveform is one volt peak to peak. So, you can now set your variable vertical gain for however many divisions you want to represent one volt using the calibrate function and you can then measure the peak-to-peak voltage of any waveform (within the scope's bandwidth) by multiplying the observed divisions by the vertical attenuator factor (X1, X10 or X100).

However, I would not use the sawtooth technique to adjust your attenuator frequency response. Firstly, it would appear from your scope photos that your sweep signal is not a good linear sawtooth, but has distortion at the ends. This is something to be looked into, but it will require a second scope. (I'm sure you have heard by now of the saying floating around ARF which goes something like: "To fix a scope requires a scope".)

Therefore, I would use the square wave technique. Even a service grade square wave generator should suffice to set up the attenuator trimmers on your relatively simple scope. I wish I had the necessary generator to set up my Tektronix 465B with 100 MHz bandwidth, but that requires a special square wave generator with nanosecond rise time. However, you don't need anything that fancy.

If you can borrow another scope, I would suggest that you look at the sweep waveform in your 470 next. Also, I would suggest that you acquire a service grade audio generator that is capable of reasonably good sine and square wave signals. This will come in handy in all sorts of ways, including your immediate requirement for setting up your 470.

Regards,

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Mon 19, 2019 5:00 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 422
Location: St. Louis, MO
You know, I got a little $10 function generator off of Amazon. It does square waves. Would that work?


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Tue 20, 2019 12:47 am 
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Location: Lincoln City, OR 97367
Greetings to ZombieElvis and the Forum:

Without knowing the specifications for your generator, it is impossible to tell for sure, but it probably will be just fine. The only thing that comes to mind is if the generator output amplitude is of a high enough level such that the display on the scope will be big enough to be usable in the X100 position.

Regards,

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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Tue 20, 2019 1:32 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11995
Location: Powell River BC Canada
The base sensitivity for the scope is 0.01 volt/inch so 100 times that would be
1 volt per inch RMS.

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Amateur Radio Literacy Club. May we help you read better.
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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Wed 21, 2019 9:15 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
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Location: St. Louis, MO
Well shoot. That little cheap $10 function generator decided to not output anything, on any setting. Time for a warranty replacement! Stay tuned.


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Wed 21, 2019 11:02 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11995
Location: Powell River BC Canada
Have you measured the input voltage and current to the function generator?
Any lights on it ?

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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Thu 22, 2019 11:50 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 422
Location: St. Louis, MO
No lights. I just tried the barrel plug on my tongue and got a tickle. That's a good enough supply check for me.

The replacement is on its way.


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 Post subject: Re: Instruction manual for an Eico 470 oscilloscope?
PostPosted: Aug Fri 23, 2019 11:34 pm 
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Joined: Jul Mon 01, 2019 4:42 pm
Posts: 422
Location: St. Louis, MO
How's this for "square" waves, 100X attenuation? Don't worry, Sine and Triangle outputs are just as weird looking.

So how would I adjust the attenuation trimmers now?


Attachments:
o scope square waves 100X.jpg
o scope square waves 100X.jpg [ 280.97 KiB | Viewed 1676 times ]
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